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Dual-entropy-source quantum random number generation based on spontaneous emission

Qiang Zhang, Dehuan Kong, Yebing Wang, Hongxin Zou, and Hong CHANG

DOI: 10.1364/OL.382067 Received 31 Oct 2019; Accepted 05 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: We propose a dual-entropy-source quantum random number generator based on atomic spontaneous emission. Using the intensity fluctuations of a coherent beam to modulate the detuning frequency of the driving field, the atomic ensemble exhibits larger fluctuations of the spontaneous emission noise. The quantumto-classical noise ratio of the measured noise is increased to 10.14 dB. After post-processing, a string of random numbers at rates up to 5.12 Mb/s is extracted, which passes all the NIST tests. The presented scheme shows the feasibility to combine multiple independent randomness sources to produce secure quantum random bits.

All optically-driven memory device for terahertz waves

Sichao Chen, Hong-Kuan Yuan, Zhao-Hui Zhai, Liang-Hui Du, Sen-Cheng Zhong, Hongfu Zhu, qiwu shi, Wanxia Huang, Ze-Ren Li, and Li-Guo Zhu

DOI: 10.1364/OL.384740 Received 29 Nov 2019; Accepted 05 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: We demonstrate an all optically-driven memory device based on vanadium dioxide (V02) for terahertz (THz) waves. By easily tuning the power of illuminating light, VO2 memory device is coded in reconfigurable and multi-level states, taking advantage of its hysteretic metal-to-insulator phase transition (MIT). Further, writing with intense femtosecond (fs) pulses, the memory effects are performed by non-thermal photo-induced MIT and resultant 2-bit coding with equilibrium time of 22 μs is demonstrated, yielding dramatically improved write rate compared to existing thermally-controlled VO2 memory device. The proposed all optically-driven VO2-based memory device paves the way for actively manipulating THz waves within robust reconfigurable high-speed memory functionality.

Mueller-Jones matrices as representing conformal Lorentz transformations

Tiberiu Tudor

DOI: 10.1364/OL.383444 Received 21 Nov 2019; Accepted 05 Dec 2019; Posted 06 Dec 2019  View: PDF

Abstract: It is shown that Mueller-Jones matrices represent conformal Lorentz transformations. Thus the necessary and sufficient condition of a polarization device to be deterministic is to be describable by a conformal Lorentz transformation

Composite Yb:YAG/sapphire thin-disk active elements for high-energy high-average power lasers

Ivan Kuznetsov, Alexey Pestov, Ivan Mukhin, Mikhail Volkov, Maria Zorina, Nikolay Chkhalo, and Oleg Palashov

DOI: 10.1364/OL.384898 Received 02 Dec 2019; Accepted 04 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: Composite active elements of thin-disk geometry with an anti-ASE cap were created for the first time from dissimilar materials (Yb:YAG and sapphire crystals) using the SADB method based on etching the surfaces with an Ar ion beam and then bringing them into optical contact. Using a sapphire anti-ASE cap allows the thermal lens optical power and the M2 factor to be reduced significantly compared to the same AE with a YAG anti-ASE cap, and M2 compared to standard Yb:YAG disks without an anti-ASE cap. Lasing with 320 W average power and ~50% slope efficiency was obtained.

Optimization of H0 photonic crystal nanocavity using machine learning

ryotaro abe, Taichi Takeda, Ryo Shiratori, Shunichi Shirakawa, Shota Saito, and Toshihiko Baba

DOI: 10.1364/OL.381616 Received 31 Oct 2019; Accepted 04 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: Using machine learning, we optimized an ultrasmall photonic crystal nanocavity to attain a high Q. Training data was collected via finite-difference time-domain simulation for models with randomly shifted holes, and a fully connected neural network (NN) was trained, resulting in a coefficient of determination between predicted and calculated values of 0.977. By repeating NN training and optimization of the Q value on the trained NN, the Q was roughly improved by a factor of 10–20 for various situations. For a 180-nm-thick semiconductor slab at a wavelength approximately 1550 nm, we obtained Q = 1,011,400 in air; 283,200 in a solution, which was suitable for biosensing; 44,600 with a nanoslot for high sensitivity. Important hole positions were also identified using the linear Lasso regression algorithm.

Multipurpose thermo-responsive hydrogel: A platform for dynamic holographic display

Juan Liu, Ata Ur Rahman Khalid, Yu Han, Naeem Ullah, Shiqi Jia, and Yongtian Wang

DOI: 10.1364/OL.383567 Received 19 Nov 2019; Accepted 03 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: Metamaterials have shown great promise for manipulating electromagnetic waves (EM), thus opening new routes for the progression of flat optics. However, post fabrication fixed structures hinder the dynamic manipulation of light. Dynamic control of EM light has been realized through different mechanisms including electrical gating, optical pumping, mechanical actuation, and temperature stimulation. Here, we are firstly proposing the plasmonic resonators mounted thermoresponsive free-standing hydrogel for holographic display which swells and collapses laterally by temperature. By taking leverage of reversible switching of hydrogel, we numerically examine polarization insensitive dynamic holographic switch by plasmonic rings/discs loaded hydrogel in reflection as a primary application. Secondly, we observe the transmitive functionality of plasmonic sector resonators mounted hydrogel, which displays persistent holographic image under swelling and collapsing conditions. This work demonstrates the potential of resonators loaded thermo-responsive hydrogel for EM waves manipulation including dynamic holography, active lensing, switching and so on.

Cross-stacking of guided-mode resonance gratings for polarization-independent flat-top filtering

Keisuke Kawanishi, Akira Shimatani, Kyu Lee, Junichi Inoue, Shogo Ura, and Robert Magnusson

DOI: 10.1364/OL.378092 Received 26 Sep 2019; Accepted 03 Dec 2019; Posted 04 Dec 2019  View: PDF

Abstract: A guided mode resonance filter (GMRF) consists of a subwavelength grating on a thin film waveguide and can provide narrowband filtering with fewer layers in contrast to a multilayer dielectric mirror. A GMRF normally shows a peaky reflection spectrum and polarization dependency. In this letter, two GMRFs are orthogonally stacked to give polarization-independent narrowband flat-top filtering. The GMRFs are designed by numerical methods and then fabricated and stacked. Each GMRF is formed by corrugation of a TiO2 grating layer on a SiN guiding core layer on a SiO2 substrate. A narrowband flat-top filter is demonstrated with 7 nm full-width at half maximum.

Resolving absolute depth in Circular-Ranging Optical Coherence Tomography by using a degenerate frequency comb

Norman Lippok and Benjamin Vakoc

DOI: 10.1364/OL.379968 Received 09 Oct 2019; Accepted 02 Dec 2019; Posted 04 Dec 2019  View: PDF

Abstract: In Fourier-domain optical coherence tomography, an interference signal is generated that spans an RF bandwidth proportional to the product of three parameters: the imaging range, the imaging speed, and the inverse of the axial resolution. Circular ranging (CR) OCT architectures were introduced to ease long-range imaging by decoupling imaging range from signal RF bandwidth. As a consequence, present CR-OCT systems resolve the relative, but not the absolute, depth location of the scatters. We introduce here a modified implementation of CR-OCT that uses a degenerate frequency comb source that allows recovery of absolute depth information while only minimally impacting the previously described RF bandwidth compression benefits of CR. We show that this degenerate frequency comb can be created by relatively simple modifications to existing frequency comb source designs, and we present absolute ranging capabilities through imaging studies and simulations.

Highly sensitive liquid-level sensor based on an optical reflective microfiber probe

Junjie Wang, Qizhen Sun, Yanpeng Li, Shijie Tan, Liuyang Yang, Fang People, Zhijun Yan, and Deming Liu

Doc ID: 380670 Received 15 Oct 2019; Accepted 02 Dec 2019; Posted 03 Dec 2019  View: PDF

Abstract: Increasing the sensitivity and miniaturizing the size of liquid-level sensors are crucial for confined installation space. Optical microfiber provides an eligible platform for miniaturization research and high-sensitivity detection beneficial from its small transverse dimension and strong evanescent field. Here, we propose and demonstrate a highly sensitive liquid-level sensor based on a compact optical reflective microfiber probe. The change in liquid level can cause a change in the proportion of microfiber length in air and liquid, resulting in the effective refractive index variation of the guiding modes. By tracking the resonant wavelength shift of the in-line Mach-Zehnder interferometer generated between the HE₁₁ and HE₁₂ modes, the liquid-level sensing can be realized. Through optimizing structure parameters of the microfiber probe, an ultra-high sensitivity of ~367.644 nm/mm is achieved in experiment, corresponding to a liquid-level resolution of ~0.003 μm, which is two to three orders of magnitude higher than other reported liquid-level sensors, to the best of our knowledge. Considering the high sensitivity and compact structure of the sensor, it has great potential in real-time intelligent monitoring of tiny changes in liquid level, such as small autonomous drones, micro- channels, etc.

Extending time-domain ptychography to generalized phase-only transfer functions

Dirk Spangenberg, Erich Rohwer, Michael Bruegmann, and Thomas Feurer

Doc ID: 379600 Received 03 Oct 2019; Accepted 02 Dec 2019; Posted 02 Dec 2019  View: PDF

Abstract: We extend the time-domain ptychographic iterative engine to generalized spectral phase-only transfer functions. The modified algorithm, i²PIE, is described and its robustness is demonstrated by different numeric simulations. The concept is experimentally verified by reconstruction of a complex supercontinuum pulse from an all normal dispersion fiber.

Engineering photonic jet array by core-shell phase diffraction grating

Cheng-Yang Liu and Yu-Lun Cheng

DOI: 10.1364/OL.382596 Received 08 Nov 2019; Accepted 02 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: In this letter, we investigated numerically and experimentally the specific spatially localized photonic jet array formed by core-shell phase diffraction gratings (PDGs). The core-shell PDG consists of a metallic shell (copper, silver, and gold) and a dielectric core (polydimethylsiloxane) with the hemispherical and triangular grooves. The finite-difference time-domain technique is employed to simulate the near-field scattering of optical radiation at different core-shell PDGs. The direct imaging of photonic jet array is performed by a scanning optical microscope for experimental verification. Our numerical and experimental results showed that each type of core-shell PDGs generate the photonic jet array with unique properties. The optical intensity of photonic jet array is greatly enhanced by gold-coating PDG due to surface plasmon resonance. The presented core-shell PDGs can be manipulated to design high-efficiency optical elements for steering photonic jet array in a wide range of applications.

Burst-mode femtosecond laser electronic excitation tagging (FLEET) for kHz–MHz seedless velocimetry

Jordan Fisher, Michael Smyser, Mikhail Slipchenko, Sukesh Roy, and Terrence Meyer

DOI: 10.1364/OL.380109 Received 11 Oct 2019; Accepted 02 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: Burst-mode femtosecond laser electronic excitation tagging (FLEET) of nitrogen is introduced for tracking the velocity field in high-speed flows at kHz–MHz repetition rates without the use of added tracers. A custom-built Nd:glass femtosecond laser is used to produce 500 pulses per burst with pulses having a temporal separation as short as 1 s, an energy of 120 µJ, and a duration of 274 fs. This enables two orders of magnitude higher measurement bandwidth over conventional kHz-rate FLEET velocimetry. Characteristics of the optical system are described, along with a demonstration of time-resolved velocity measurements with ~0.5% precision in a supersonic slot jet.

SnSSe as a saturable absorber for ultrafast laser with remarkable stability

Wen Liu, Mengli liu, ximei liu, Ming Lei, and Zhiyi Wei

DOI: 10.1364/OL.380183 Received 10 Oct 2019; Accepted 01 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: Due to the unique and versatile properties, two-dimensional nanomaterials have attracted enormous attention in the fields of electronics and optoelectronics. As a ternary metal sulfide which similar to MoS2, SnSSe is confirmed to have great potential in optoelectronic applications in near-infrared region, especially in solar energy conversion. Here, for the first time, SnSSe is investigated for the generation of mode-locked solitons. The prepared SnSSe SA exhibits large modulation depth of 56.75%. For the saturable absorption characteristics of SnSSe saturable absorber (SA), mode-locked pulses as short as 158.6 fs with signal-to-noise ratio of 94 dB are generated at 1560.9 nm. The nonlinear exploration of SnSSe offers the possibility to explore further applications of SnSSe in near-infrared region, especially for ultrafast photonic devices and modulators.

Simultaneous temporally and spectrally resolved Raman coherences with single-shot fs/ns rotational CARS

Ali Hosseinnia, Maria Ruchkina, Pengji Ding, Per-Erik Bengtsson, and Joakim Bood

DOI: 10.1364/OL.380247 Received 14 Oct 2019; Accepted 01 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: A novel technique for studies of the dynamics of molecular coherences has been developed. The concept is based on prompt excitation using broadband femtosecond laser pulses, whereupon a narrowband nanosecond laser pulse probes the fast dynamics of the coherences. Detection of the spectrally dispersed coherent signal using a streak camera allows simultaneous spectrally and temporally resolved studies of all excited coherences in a single-shot acquisition. Here we demonstrate the high capacity and versatility of this hybrid femtosecond/nanosecond coherent anti-Stokes Raman scattering (CARS) technique through some illustrative examples, all single-shot measurements, namely time-resolved studies of rotational Raman coherences in nitrogen and air, dynamics of Stark effect on rotational lines, and beating phenomena originating from close-lying rotational lines.

A phase-shifted FBG modulated by a hollow cavity for measuring gas pressure

Junxian Luo, Shen Liu, YuanYuan Zhao, Yanping Chen, Kaiming Yang, Kuikui Guo, Jun He, Changrui Liao, and Yiping Wang

DOI: 10.1364/OL.381452 Received 28 Oct 2019; Accepted 01 Dec 2019; Posted 05 Dec 2019  View: PDF

Abstract: A novel gas pressure sensor based on a phase-shifted fiber Bragg grating (PS-FBG) modulated by a hollow cavity is proposed and demonstrated. The device was fabricated by fusing a hollow-core fiber (HCF) between two single-mode fibers (SMFs) exhibiting FBGs inscribed using line-by-line femtosecond (fs) laser etching. A pair of micro-channels were drilled orthogonally to the HCF using an fs laser, to allow the argon gas to get in and out freely.Such sensor exposes a highspectrum finesse, e.g. Q-factor of ~7302, which can be improved by decreasing the grating pitch quantity. Furthermore, a high gas pressure sensitivity is obtained to be 1.22nm/Mpa, corresponding the improved sensor with grating pitch quantity of300 and hollow cavity length of 88.3μm.In addition, the device exhibited a low temperature sensitivity of 8.40 pm/℃.

High-efficient couplers for graphene surface plasmon polaritons in mid-infrared region

Longfang Ye, Kehan Sui, and Hao Feng

Doc ID: 380173 Received 10 Oct 2019; Accepted 01 Dec 2019; Posted 02 Dec 2019  View: PDF

Abstract: We numerically demonstrate a novel variety of high-efficient couplers for mid-infrared graphene surface plasmon polaritons (SPPs). The proposed couplers are composed of a dual parabolic tapered transition to compress and couple the SPPs of GaAs slab waveguide into the graphene layer. The dispersion relation, field distributions, transmittance, and coupling efficiency of the couplers are systematically analyzed. It is found that broadband coupling transmission with a transmittance around 0.3 is achieved for the coupler without a silver substrate. To further reduce radiation and enhance the transmittance, a silver substrate is introduced in the proposed coupler design, which achieves a transmittance over 0.5 ranging from 1960 cm-1 to 20 cm-1 with a peak transmittance of 0.75. Furthermore, both couplers with and without silver substrate achieve a similar coupling efficiency of more than 48% in the whole wavelength range of 1900 - 2400 cm-1 and a coupling efficiency peak of over 80% around 2120 cm-1. This work may provide an efficient excitation method for graphene surface plasmon polaritons, which is of great importance for the development of various graphene plasmonic devices.

pO2-weighted Imaging In Vivo by Delayed Fluorescence of Intracellular Protoporphyrin IX

Marek Scholz, Xu Cao, Jason Gunn, Petr Brůža, and Brian Pogue

Doc ID: 380418 Received 30 Oct 2019; Accepted 01 Dec 2019; Posted 02 Dec 2019  View: PDF

Abstract: We report on imaging of tissue oxygen by means of time-gated wide-field lifetime imaging of the microsecond-scale delayed fluorescence from Protoporphyrin IX (PpIX). PpIX is endogenously produced from a clinically used δ-aminolevulinic acid (5-ALA) by most cells. The lifetime of delayed fluorescence is lengthened by the absence of oxygen to quench its triplet state. Here, images of the delayed emission from skin of human and nude mice were captured after topical application of 5-ALA, using a pulsed 635nm excitation. Macroscopic lifetime-based images were found to be related to the tissue oxygenation, and obtained with a low light dose (~10 mJ/cm²) and capture times of a few seconds.

Mapping a quantum walk by tuning the coupling coefficient

Kian Fong Ng, Manuel Rodrigues, Jose Viana-Gomes, Alexander Ling, and James Grieve

Doc ID: 376022 Received 01 Oct 2019; Accepted 01 Dec 2019; Posted 02 Dec 2019  View: PDF

Abstract: We present a method to map the evolution of photonic random walks that is compatible with nonclassical input light. Our approach leverages a newly developed flexible waveguide platform to tune the jumping rate between spatial modes, allowing the observation of a range of evolution times in a chip of fixed length. In a proof-of-principle demonstration we reconstruct the evolution of photons through a uniform array of coupled waveguides by monitoring the end-face alone. This approach enables direct observation of mode occupancy at arbitrary resolution, extending the utility of photonic random walks for quantum simulations and related applications.

Method to eliminate pseudoscopic issue in integral imaging 3D display by using transmissive mirror device and light filter

Han-Le Zhang, Huan Deng, Hui Ren, Xin Yang, Dahai Li, and Qiong-Hua Wang

Doc ID: 377465 Received 12 Sep 2019; Accepted 30 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: We propose an optical method to eliminate pseudoscopic issue in integral imaging 3D display by using a transmissive mirror device (TMD) and a light filter. Object light rays passing through the TMD can form an undistorted and depth inverted real image. Therefore, the TMD can eliminate the pseudoscopic issue existing in the traditional integral imaging 3D display. However, two ghost images are appeared in integral imaging 3D display using the TMD. After studying the causes of the ghost images, a light filter is designed and fabricated to eliminate the ghost images. An integral imaging 3D display using the TMD is developed and it presents high quality 3D image without pseudoscopic issue.

An adaptive electrofluid-actuated liquid lens

Xiang Huang, Hang Jin, Siying Lin, Zhenxiang Bu, Zhihong Lin, Wenchang Tu, and Lingyun Wang

Doc ID: 379052 Received 01 Oct 2019; Accepted 30 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: We present a novel adaptive liquid lens actuated by electrofluid. The deformation of electrofluid under the combined action of vertical electric and magnetic fields controls the hydraulic pressure in the lens chamber. Both study of electrohydrodynamics and of optical properties of the prototype have been carried out. The measured focal length of the liquid lens decreases from 34.55 mm to 5.12 mm, as the current increases from -3 A to 5 A. The electrofluid-actuated lens exhibits some attractive features compared with the conventional mechanical driven lens, such as high integration, easy control and low cost.

Microwave photonic notch filter with tunable frequency and bandwidth based on gas absorption

Yong Kang Dong, Yuan Ziyue, and Xiutao Lou

Doc ID: 380395 Received 15 Oct 2019; Accepted 30 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: We propose and demonstrate a high-performance microwave photonic notch filter (MPNF) based on gas absorption with favorable tunability and a high rejection ratio. In the demonstration experiments, acetylene gas is used to selectively absorb the single sideband produced by phase modulation, and correspondingly to suppress the generated microwave signal. The filter center frequency and bandwidth can be separately tuned by changing the carrier laser frequency and gas pressure. The proposed MPNF achieves a continuously tunable frequency from 2 to 20 GHz and a 10-dB bandwidth from 0.44 to 5.89 GHz with a high rejection ratio over 60 dB, which is expected to exceed 100-dB in theory, showing great potentials for various applications such as advanced communication and radar.

Single-shot achromatic imaging for broadband soft X-ray pulses

Satoru Egawa, Hiroto Motoyama, Atsushi Iwasaki, Gota Yamaguchi, Takehiro Kume, Kaoru Yamanouchi, and Hidekazu Mimura

DOI: 10.1364/OL.381538 Received 29 Oct 2019; Accepted 30 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: An achromatic soft X-ray imaging system based on a transmission microscope equipped with a pair of Wolter mirrors was constructed. The two Wolter mirrors for the condenser and objective were fabricated precisely using an electroforming replication process. Samples were illuminated by broadband high harmonic pulses in the wavelength range of 26 nm to 35 nm via the condenser mirror, and transmission bright-field images without chromatic aberration were formed by the objective mirror. A single-shot image illuminated by a femtosecond laser pulse was recorded at a spatial resolution of about 200 nm. The fundamental capability of the microscope to realize broadband images without chromatic aberration will lead to the development of soft X-ray microscopes with extremely short illumination pulses on the order of attoseconds.

Circular polarization of Cherenkov radiation assisted by metasurface on waveguide

Wenjia Li, Jianlong Liu, Yang Gao, Keya Zhou, and Shutian Liu

DOI: 10.1364/OL.383285 Received 14 Nov 2019; Accepted 29 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: We propose an orientation-dependent polarization manipulation by Cherenkov radiation (CR) in a silicon-on-insulator (SOI) waveguide with metasurface. By putting an electron bunch passing near the SOI waveguide, the CR excites the fundamental TE-like mode with an ultra-high mode purity. The spin state of the decoupled light is determined by the direction of the electron motion, and the maximum magnitude of the normalized Stokes polarization parameter $S_3$ approaches $\pm 1$ corresponding to the right and left circularly polarized lights. This work provides a new way to achieve CR with spin angular momentum in an SOI waveguide and offers a platform to study the interaction between electron and light with nanostructures on-chip.

Real-time monitoring of adaptive lenses with hightuning range and multiple degrees of freedom

Wenjie Wang, Katrin Philipp, Nektarios Koukourakis, and Juergen Czarske

Doc ID: 381346 Received 25 Oct 2019; Accepted 29 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: Adaptive lenses are widely used to implement fast axial scans in various microscopes, without any mechanical movement. However, driving the lens to achieve the desired behaviour is challenging making in-situ monitoring and control of the lens often necessary when inserted into a microscope. But the demand for the monitoring techniques can be high when lenses with large tuning range or multiple degrees of freedom are employed.We analyze the performance of partitioned aperture wavefront (PAW) as a tool for in-situ monitoring of adaptive lenses. PAW has the advantage that it enables measurements of large input wavefront angles and thus allows to monitor the behaviour of high tuning range lenses with just a single beam path. We apply PAW to characterize an adaptive lens with high tuning range of +/-20 dpt and to control the behaviour of a novel adaptive lens with two actuators that allows to tune focal length and spherical aberrations simultaneously.

A low crosstalk interferometric fiber optic surface plasmon resonance sensor for dual-parameter measurement

Duo Yi, yuzhi chen, Youfu Geng, Teng Fei, Yong Li, Xuejin LI, and Xue Ming Hong

Doc ID: 382749 Received 08 Nov 2019; Accepted 29 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: This study proposes an interferometric fiber optic surface plasmon resonance (SPR) sensor, and it is based on Single Mode Fiber-No Core Fiber-Single Mode Fiber (SMF-NCF-SMF) structure with partially deposited gold film layer. When compared with the previous studies, the main contribution of this study is the introduction of multimode interference into the SPR sensors, hence both the surface plasmon resonance and the multimode interference mechanism are excited in a single sensor structure for the dual-parameter measurement. The measurement process is realized based on two individual sensing mechanisms and the separated spectral regions (visible or near-infrared), therefore the crosstalk between the two measured parameters is largely suppressed and has been verified experimentally insignificant. Furthermore, the obvious interference effect can be used to measure a great number of physical parameters, hence the application scope of the proposed multiplex sensor is largely extended not limited to the biochemical field for the traditional SPR sensors.

Optical scrambling system for image authentication

Marie DEJEAN, Jean Louis de Bougrenet de la Tocnaye, and Vincent Nourrit

DOI: 10.1364/OL.381297 Received 24 Oct 2019; Accepted 29 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: The continuous development of new authentication techniques is necessary to prevent illegal data access from unauthorized users or counterfeiting. In this paper, we present a simple optical method to decode encrypted image using a multi-scopic optical system. The method uses a scrambled lens-let array which provides a high level of security. In a simple configuration, the encrypted image is scrolled in front of the multi-scopic imaging system. Due to a particular arrangement of lens-lets, the image will only be correctly imaged at a unique position with respect to the imager. Experimental demonstrations are presented and potential applications discussed.

Improving the reflectivity and color contrasts of phase-change materials by vacancy reduction for optical-storage and display applications

Jianbo Wang, Qian Li, Shuaipeng Tao, Zhoubo Xia, Yuankai Li, Yan Liu, Zhiqing Gu, and Chaoquan Hu

Doc ID: 380677 Received 07 Nov 2019; Accepted 28 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: High reflectivity/color contrasts are crucial for phase-change materials (PCMs) in optical-storage and display applications. However, the relationship between phase change and reflectivity/color contrasts and how to improve the contrasts has not been well explored. Here, we find that phase-change-induced reflectivity/color contrasts arise from electron delocalization and subsequent extinction coefficient enhancement, rather than refractive coefficient enhancement that we thought previously. Reducing vacancies can significantly increase the reflectivity contrast and color contrast of PCMs films by 83.2% and 38.5%, respectively. These new insights are demonstrated through our experiments, theoretical calculations, spectral fittings and simulations on Ge₁Sb₄Te₇, Ge₂Sb₂Te₅, Ge₈Sb₂Te₁₁ and GeTe.

Nonlinear optical properties in semiconductor double quantum wires coupled to a quantum-sized metal nanoparticle

Ying Su, Kangxian Guo, Guanghui Liu, Tao Yang, Qiucheng Yu, Meilin Hu, and Yanlian Yang

DOI: 10.1364/OL.377453 Received 11 Sep 2019; Accepted 28 Nov 2019; Posted 05 Dec 2019  View: PDF

Abstract: Previously, much attention was focused on nonlinear optical effects (NOEs) in hybrid system made of a semiconductor quantum system (SQS) and a classical-sized MNP, while reports on NOEs in double SQSs coupled to a quantum-sized MNP are still lack. We theoretically investigate linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs) of two quantum wires (QWs) separated by a quantumsized MNP using density matrix method and dielectric quantum theory. The exciton-plasmon coupling and the dipole-dipole interaction (DDI) between the two QWs are taken into account. We find that the magnitudes of the linear and nonlinear OACs (RICs) from the QWs are enhanced by one order of magnitude in contrast to the case without MNP, due to the exciton-plasmon coupling and the DDI between the two QWs. Quantum size effect in MNP induces a pronounced enhancement in the magnitudes of the linear and nonlinear OACs (RICs) with the increase of the MNP radius. Furthermore, the optical responses can be further strengthened via increasing the MNP radius or decreasing the radius and gap of the QWs, owing to the enhanced exciton-plasmon coupling and the DDI between the two QWs. Moreover, the magnitudes of the total OACs (RICs) are reduced by increasing the optical intensity, along with a splitting effect of the OACs under strong optical intensity. Our results provide the possibility of designing the hybrid nanostructures with large nonlinearity for applications in nano-devices such as optical switches and amplifiers.

Orthogonally polarized frequency combs in a mode-locked VECSEL

Krassimir Panajotov, Andrei Vladimirov, and Mustapha Tlidi

Doc ID: 380033 Received 11 Oct 2019; Accepted 27 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: We introduce a spin-flip model for a Vertical External-Cavity Surface-Emitting Laser (VECSEL) with a saturable absorber. We demonstrate the possibility, due to the spin flip dynamics, to generate two orthogonally linearly polarized frequency combs in the mode-locked regime. The two combs are shifted in wavelength due to the birefringence in the VECSEL gain and/or saturable absorption mirror. We show that polarization degree of freedom may also lead to several pulses generated per roundtrip in the two orthogonal linear polarizations and to more complicated dynamics with both linear polarizations exited.

Fiber-optic joint time and frequency transfer with the same wavelength

Jialiang Wang, Chaolei Yue, Yueli Xi, Yanguang Sun, Nan Cheng, Fei Yang, Mingyu jiang, Jianfeng Sun, You-Zhen Gui, and Haiwen Cai

Doc ID: 379338 Received 02 Oct 2019; Accepted 27 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: Optical fiber links have demonstrated their ability to transfer the ultra-stable clock signals. In this paper we propose and demonstrate a new scheme that time and frequency signals in the same direction can be transmitted through the same wavelength based on coherent demodulation technique. Time signal is encoded to the optical carrier using electro optic modulator (EOM) by phase modulation and makes sure the frequency signal free from interference with single pulse. The noise changes caused by the fluctuations of the transfer links are actively cancelled at local site by optical delay lines. Radio frequency with 1GHz and time signal with one pulse per second (1PPS) transmitted over a 110km fiber spools are obtained. The experimental results demonstrate that frequency instabilities of 1.7E-14 at 1s and 5.9E-17 at 104s. Moreover, time interval transfer of 1PPS signal reaches sub-ps stability after 1000s. This scheme offers advantages with respect to reduce the channel in fiber network, and can keep time and frequency signal independent of each other.

High-quality integrated microdisk resonators in the visible-to-near-infrared wavelength range on a 3C-SiC-on-Insulator Platform

Ali Adibi, Tianren Fan, Xi Wu, Ali Asghar Eftekhar, Matteo Bosi, Hesam Moradinejad, and Eric Woods

Doc ID: 380728 Received 17 Oct 2019; Accepted 26 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We report the first demonstration of high-quality integrated microdisk resonators (MDRs) on a 3C-silicon carbide-on-insulator (SiCOI) platform working over a wide bandwidth from visible to near-infrared (NIR) wavelengths. We show record-high Qs of 242,000 at 1550 nm wavelengths using a 60 μm-radius MDR, 112,000 at 770 nm wavelengths using a 20 μm-radius MDR, and 83,000 at 650 nm wavelengths using a 10 μm-radius MDR based on high-quality 3C-silicon carbide (SiC) films with surface roughness as low as 1.4 Å, achieved by sample-transfer bonding, and precise chemical-mechanical polishing (CMP) of the SiC film to remove growth defects. Our study of 3C-SiC films grown on silicon (Si) using transmission electron microscopy (TEM) shows that even considerably higher-quality single-crystalline SiCOI can be achieved by flipping and thinning down an ultra-thick (~5-10 μm) 3C-SiC film grown on Si. The SiCOI platform can be used to realize ultra-wideband high-quality SiC devices that are desirable for applications in nonlinear and quantum photonics.

Design of highly-selective radiative-cooling structure accelerated by materials informatics

Jiang Guo, Shenghong Ju, and Junichiro Shiomi

Doc ID: 376613 Received 29 Aug 2019; Accepted 26 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: Materials informatics is a data-driven approach that integrates material property simulation/experiment with informatics algorithm to accelerate the materials design. In this work, we report the optimization design of thermal photonic structure for radiative cooling application by the method combining the rigorous coupled wave analysis and Bayesian optimization. The structure with optimal thermal radiative property can be obtained by calculating only less than 1% of total candidate structures. The present work is the first trial using Bayesian optimization for radiative cooling device design and successfully tailored the thermal emittance selectively falling within the atmospheric window by hybrid grating and multilayer structures.

Angled fiber-based Fabry-Perot interferometer

Xinpu Zhang, Lixia Li, Xihua Zou, Bin Luo, Wei Pan, lianshan Yan, and Qiang Wu

Doc ID: 381041 Received 24 Oct 2019; Accepted 26 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: Herein, we proposed and experimentally demonstrated a novel all-fiber Fabry-Perot (FP) interferometer which is formed by a simple angled fiber which can function as a beam splitter. According to the principle of the angled fiber, we verify the influence of oblique angle on light propagation path and light intensity ratio. Subsequently, angled fiber-based FP interferometers are experimentally demonstrated, and the influence of oblique angle on the visibility of interference fringes and temperature characteristics is investigated. Finally, the temperature characteristics of this proposed FP interferometer is investigated experimentally, the temperature sensitivity is 12.62 and 10.89pm/°C for 42 ° and 40 ° angled fiber-based fiber FP interferometer, respectively. This proposed FP interferometer is fabricated by using a simple angled fiber, which has advantages of ease fabrication and all-fiber characteristic, and hence can meet the requirements of mass production and high stability in various practical application areas.

Broadband Optical Modulation in Zinc Oxide based Heterojunction via Optical Lifting


DOI: 10.1364/OL.379257 Received 30 Sep 2019; Accepted 26 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: Broadband electro-absorptive optical modulation in zinc oxide (ZnO) based heterojunction is demonstrated. The presence of high-density two-dimensional electron gas (2DEG) at the bottom of conduction band offset in heterojunction is shown to exhibit electrically tunable optical absorption in the regions well below the material band gap. Electrons confined near the heterojunction of MgZnO-CdZnO are lifted across the potential barrier on optical excitation. Optical modulation with an extinction ratio of 8 dB is reported at an operating wavelength of 527 nm. The extinction ratio remains around 7-8 dB over a wide bandwidth of 115 nm providing an excellent opportunity to explore ZnO based heterojunctions to realize broadband optical modulator for applications in optical communication and interconnects.

Beyond 53% IQE in AlGaN quantum well at 326nm UVA emission and single peak operation of UVA LED

Muhammad Khan, RYOHEI TAKEDA, Yoichi Yamada, N Maeda, Masafumi Jo, and Hideki Hirayama

DOI: 10.1364/OL.376894 Received 05 Sep 2019; Accepted 26 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: AlGaN-based ultraviolet-A (UVA) light-emitting-diodes (LEDs) at emission under 330 nm are of great importance for numerous practical applications including medicine and photochemical technologies. In this report, a highly relaxed n-AlGaN electron injection layer (EIL), underneath the multi-quantum wells (MQWs), for the suppression of both threading dislocations densities (TDDs) and piezoelectric effect was attempted. When the Ga-rich n-AlGaN EIL in the UVA LED was relaxed up to 75%, the full width at half maximum (FWHM) values of the X-ray rocking curves (XRCs) for the (10-12) planes were reduced from our previous value of 793 arcsec to approximately 564 arcsec. Subsequently, a maximum light power of 3.1 mW was achieved in the 326nm-band UVA LED. However, carrier’s confinement issue in the MQWs was observed. To resolve the issue of carrier confinement in the MQWs, we provide a short roadmap for experimental efforts to realize an internal quantum efficiency beyond 53% in an AlGaN UVA-MQWs.

Characterizing the topological charges distribution of the elliptical beams with vortex lattices

Yung-Fu Chen, Y. H. Hsieh, Y. H. Lai, and M. X. Hsieh

Doc ID: 384384 Received 26 Nov 2019; Accepted 26 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: A new numerical approach is proposed to analyze the topological charges distribution of elliptical beams with vortex lattices generated from the astigmatic transformations of Hermite-Gaussian beams. The birth and death of the topological charges for elliptical beams are thoroughly verified by continuously changing the astigmatic strength. The theoretical explorations are exploited to make a complete comparison with experimental measurements which are obtained from an off-axis pumped solid-state laser with an external astigmatic mode converter and a Mach-Zehnder interferometer. The good agreements between theoretical and experimental results provide the feasibility to flexibly manipulate the topological charges of vortex lattices in further applications.

Phase shifting digital holography with Hanbury Brown-Twiss approach

li Chen, Rakesh Singh, Ziyang Chen, and Jixiong Pu

Doc ID: 380703 Received 17 Oct 2019; Accepted 24 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We report a phase shifting holography for coherence waves in the Hanbury- Brown and Twiss (HBT) approach. This technique relies on the wave nature and interference of the coherence waves in the two-point intensity correlation. Experimentation is carried out by recovery of the complex coherence using the phase shifting in the intensity correlation. As an application, imaging of the phase target obscured by a random scattering medium is demonstrated and results are presented for three different cases. These results are also compared with imaging of the targets in absence of the scatting medium by a conventional phase shifting digital holography.

Double speckle pattern interferometric measurements for micro-angular displacement and the center of rotation

Fujun Yang, Minyang Wu, Guangchen Lu, and Yinhang Ma

Doc ID: 380274 Received 11 Oct 2019; Accepted 24 Nov 2019; Posted 26 Nov 2019  View: PDF

Abstract: Double speckle pattern interferometry is presented for the measurement of in-plane rotation angle, sign and the center of rotation. The technique employs two conventional in-plane sensitive electronic speckle pattern interferometry system combined with two-wavelength laser illumination and phase-shifting method. Angular displacement of micro-rotation including the sign is determined from the wrapped phase difference, and the center of rotation is located by using wrapped phase difference maps related to two directional displacement. The test setup is described and experimental results indicate that the system can provide angular displacement measurement by accuracy of 1.8 arcsec.

Optical transistor and router application of AT-Splitting in various solid atomic-like media

Faizan Raza, HUANRONG FAN, Habib Ullah, FAISAL NADEEM, HASNAIN ALI, JINYANG LI, and Yanpeng Zhang

Doc ID: 381155 Received 23 Oct 2019; Accepted 23 Nov 2019; Posted 26 Nov 2019  View: PDF

Abstract: We compare the Aulter-Townes (AT)-splitting in Eu3+:YPO4, Pr3+:YPO4 and Pr3+:Y2SiO5 crystals. The AT-splitting in Pr3+:Y2SiO5 is stronger than other two doped crystals, while Pr3+ has stronger dressing than Eu3+ in host material of YPO. The stronger dressing in YSO is attributed to C2h symmetry of the YSO crystal and its non-degeneracy, making dressing sensitive in doped material. By investigating relationship between spectral AT-splitting (SAT-splitting) and temporal AT-splitting (TAT-splitting), we observed that TAT-splitting depends upon dressing effect and phonon assisted non-radiative transition whereas SAT-splitting results only from dressing effect. Based on our results, we proposed a model for an optical router and transistor (amplifier and switch). The router action results from the SAT- and TAT-splitting while the transistor was realized by a switch from bright to dark dressed states

Dynamics of optical polarizability of liquid water exposed to intense laser light

Vitali Kononenko, Viktor Gololobov, and Vitaliy Konov

Doc ID: 380686 Received 18 Oct 2019; Accepted 23 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: Variations in the optical properties of pure water induced by a femtosecond laser (wavelength 800 nm, intensity ~10^{12} W/cm^2) were studied by a pump--probe interferometric technique. Laser photoionization was shown to increase both the refractive index and absorbance of the water. While the absorption dynamics was found to be in a good agreement with previous studies, the temporal behavior of the refractive index exhibited novel features. It was found that the always-positive refractive index contains distinct peaks at the beginning and end of the laser pulses. This behavior was attributed to the Kerr effect in water molecules and in wet/hydrated electrons produced by photoionization, respectively.

Snapshot hyperspectral light field imaging using Image Mapping Spectrometry

Qi Cui, Jongchan Park, R. Theodore Smith, and Gao Liang

DOI: 10.1364/OL.382088 Received 31 Oct 2019; Accepted 23 Nov 2019; Posted 04 Dec 2019  View: PDF

Abstract: In this letter, we present a snapshot hyperspectral light field imaging system using a single camera. By integrating an unfocused light field camera with a snapshot hyperspectral imager, the Image Mapping Spectrometer, we captured a 5D (x,y,u,v,λ) ( x,y, spatial coordinates; u,v, emittance angles; λ, wavelength) datacube in a single camera exposure. The corresponding volumetric image (x,y,z) at each wavelength is then computed through a scale-depth space transform. We demonstrated the snapshot advantage of our system by imaging the spectral volumetric scenes in real time.

Revelation and addressing of accommodation shifts in microlens array-based 3D near-eye light field displays

Zong Qin, Jui-Yi Wu, Ping-Yen Chou, Yu-Ting Chen, Cheng-Ting Huang, Nikhil Balram, and Yi-Pai Huang

Doc ID: 378740 Received 24 Sep 2019; Accepted 22 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: In a 3D near-eye light field display (LFD) using microlens array-based integral imaging, the accommodation response is presumed to exactly coincide with the reconstructed depth plane (RDP), which, however, has been little examined. By employing a highly accurate image formation model to analyze retinal images, the accommodation response is revealed to significantly shift towards the central depth plane (CDP) because of defocusing. The shift is quantitatively characterized for various CDPs and RDPs with a preliminary verifying experiment, to provide content producers with an approach to address the accommodation shift to fully mitigate the vergence-accommodation conflict.

Axial super-resolution using a double-zone pinhole in a confocal microscope

Xiangdong Huang and Jiubin Tan

Doc ID: 379511 Received 02 Oct 2019; Accepted 22 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: A double-zone pinhole intensity ratio measurement method is proposed for confocal microscopy based on the inverse phase characteristics of the axial response between the central and annular portions of the spot. Simulation and experimental results show that when the normalized optical radius of the central region is 3.2 and the peak values of the axial response of the two regions are similar, the central lobe of the axial characteristic curve can be compressed by 72.8%, without changing the original structure of the system. This simple method can effectively suppress both light-source intensity drift and changes in the measured surface reflectance.

Stabilization of passive harmonic mode-locking in fiber ring laser

Dmitry Korobko, Regina Gumenyuk, and Igor Zolotovskii

Doc ID: 380064 Received 09 Oct 2019; Accepted 22 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: We propose the model of harmonically mode-locked soliton fiber ring laser based on the nonlinear polarization rotation taking into account the gain depletion and recovery effects. It is shown that a specific timing jitter could arise in such lasers since the pulses in the cavity are not strongly identical. To suppress the jitter and stabilize harmonic mode-locking operation a method using a small frequency shift followed by the laser radiation filtering is described. The performed numerical simulation shows that the proposed method is able to provide extremely stable harmonic mode-locking in soliton fiber ring laser.

Graphene decorated twin-core fiber Michelson interferometer for all-optical phase shifter and switch

Chunying Guan, Rang Chu, YUTAO BO, Jing Liu, Jin-hui Shi, jing Yang, Peng Ye, ping li, Jun Yang, and Libo Yuan

Doc ID: 380516 Received 16 Oct 2019; Accepted 22 Nov 2019; Posted 27 Nov 2019  View: PDF

Abstract: We investigated all-optical phase shifter and switch based on graphene decorated side-polished twin-core fiber (SPTCF) Michelson interferometer (MI). The MI was fabricated by tapering the splicing point between the TCF and single mode fiber (SMF). The flat surface of exposed polished core in the TCF was coated with monolayer graphene. A 980 nm pump laser is used to produce a photothermal effect. The graphene’s ohmic heating changes effective refractive index of the exposed core, resulting in the phase shift of MI. The MI with a polished length of 5 mm has a significant modulation phase shift with a nearly linear slope of 0.0102 π∕mW near the wavelength of 1550 nm and can obtain an extinction ratio of 7 dB for optical switching with a rise (fall) time of 55.8 ms (15.5 ms). The high-density integration, all-optical control, and ease of fabrication enable the proposed device to have great potentials in the miniaturization of optical devices and all-optical signal processing.

OpenWSI: an open-source, low-cost, and high-throughput whole slide imaging system via single-frame autofocusing

Guoan Zheng, Chengfei Guo, Zichao Bian, Shaowei Jiang, Michael Murphy, Jiakai Zhu, Ruihai Wang, Pengming Song, Xiaopeng Shao, and yongbing zhang

Doc ID: 376437 Received 27 Aug 2019; Accepted 22 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: Recent advancements in whole slide imaging (WSI) have moved pathology closer towards digital practice. Existing systems require precise mechanical control and the cost is prohibitive for most individual pathologists. Here we report an open-source WSI system, termed OpenWSI, which is built using off-the-shelf components including a programmable LED array, a photographic lens, and a low-cost computer numerical control (CNC) router. Different from conventional WSI platforms, our system performs real-time single-frame autofocusing using color-multiplexed illumination. For axial positioning control, we perform coarse axial adjustment using the CNC router and precise adjustment using the ultrasonic motor ring in the photographic lens. By using a 20X objective lens, we show that the OpenWSI system can acquire images of a 225-mm² area in ~2 mins, with an imaging throughput comparable to existing high-end platforms. We have also provided an open-source implementation protocol for the broad research community. The reported system offers a turnkey solution to transform the high-end WSI platforms into one that can be made broadly available and utilizable without loss of capacity.

Fine-tuning of the optical properties of light cagesusing dielectric nanofilms

Bumjoon Jang, Julian Gargiulo, Mario Ziegler, Ron Fatobene Ando, Uwe Hübner, Stefan Maier, and Markus Schmidt

Doc ID: 376540 Received 28 Aug 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: Here we show that the optical properties of direct-laser-written on-chip hollow-core waveguides – so-called light cages – can be controlled to a very high degree by dielectric nanofilms. Using low-temperature atomic layer deposition (ALD), alumina nanofilms were concentrically deposited on the high-aspect strands which surround the central air core and confine the light via the anti-resonant effect. In accordance with modal cut-off simulations without any free parameters, a linear spectral shift of the resonances with increasing film thickness is experimentally observed. The phenomenon is explained by a shift of the dispersions of cladding supermodes. As neither cage geometry nor polymer is affected by the film deposition our results suggest atomic layer deposition to be an essential tool for fine-tuning the properties of hollow core light cages and to protect them from aggressive substances, being relevant for, e.g., bioanalytics or quantum technology.

High sensitivity X-ray imaging of lead halide perovskite single crystals scintillator

Qiang Xu, Wenyi Shao, Yang Li, Zhichao Zhu, Bo Liu, Xiaoping Ouyang, and Liu Jun

Doc ID: 378747 Received 26 Sep 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: Low dose rate detection and high contrast are required to reduce unwanted ionization irradiation for X-ray imaging procedure. Recently, low-cost solution-processed hybrid lead halide perovskite has been demonstrated for direct X-ray detection. However, the performances are limited by the relative poor charge collection. Here, we report an organic-inorganic perovskite single crystals scintillator with high sensitivity for X-ray imaging. High-quality scintillator crystals have been synthesized using the solution-processed method at low temperature with X-ray excited light emission wavelength of 432nm. The lowest detectable dose rate is 114.7 nGy s−1, which is comparable with the best perovskite-based photoconductor X-ray detector for 50keV X-ray. We archived a high contrast X-ray image that proves the feasibility for medical applications.

Octave-spanning coherent supercontinuum generation in an AlGaAs-on-insulator waveguide

Bart Kuyken, Minhao Pu, Maximilien Billet, François Leo, and Kresten Yvind

Doc ID: 379426 Received 28 Oct 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: We demonstrate supercontinuum generation over an octave spaning from 1055 to 2155 nm on the highly nonlinear aluminum gallium arsenide-on-insulator (AlGaAsOI) platform. This is enabled by the generation of two dispersive waves in a 3-mm-long dispersion-engineered nano-waveguide. The waveguide is pumped at telecom wavelengths (1555 nm) with 3.6 pJ femtosecond pulses . We experimentally validate the coherence of the generated supercontinuum around the pump wavelength (1450-1750 nm), and our numerical simulation shows a high degree of coherence over the full spectrum. © 2018 Optical Society of America

High-Resolution Spectroscopy and Laser Frequency Stabilization Using a Narrow-Linewidth Planar-Waveguide External Cavity Diode Laser at 1063 nm

Feng-Lei Hong, Haruki Sakagami, Hiroki Yamamoto, Sho Okubo, Hajime Inaba, and Kazumichi Yoshii

Doc ID: 380881 Received 23 Oct 2019; Accepted 21 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: We demonstrate high-resolution spectroscopy of molecular iodine using the second harmonic generation of a 1063-nm planar-waveguide external cavity diode laser. The hyperfine components of the R(38)32-0 transition are observed with a signal-to-noise ratio of approximately 180 over a bandwidth of 1 kHz. The diode laser is frequency-stabilized to the observed hyperfine component a10 and achieves a stability at a level of 10-¹³ for averaging time of 1 s. The absolute frequency of the a10 hyperfine component of the R(38)32-0 transition is determined as 564 010 092 161(6) kHz. The frequency-stabilized diode laser has various applications, including optical frequency combs and interferometric measurements.

Tight-focusing properties of linearly polarized circular Airy Gaussian vortex beam

Liping Zhang, Jingli Zhuang, and Dongmei Deng

Doc ID: 383517 Received 15 Nov 2019; Accepted 21 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: We show the tightly focusing properties of the linearly polarized circular Airy Gaussian vortex beam (CAiGVB) by high numerical aperture (NA) objective lens, and the light intensity distributions will exhibit diversities with different positions of the vortex pairs (on-axis or off-axis vortex pairs). By choosing different optical distribution factors, the CAiGVB would turn into circular Airy vortex beam or Gaussian vortex beam, and the depth of focus (DOF) can also be controlled. It has been known that the vortex beam will possess both orbital and spin angular momentum. The spin density vector will change its direction in three dimensional space during the beam propagation as long as it is not purely transverse or longitudinal, which will cause to the 3D polarization ellipse topologies. In contrast, the polarization topologies will degenerate into 2D when the spin density vector is purely transverse or longitudinal. Furthermore, the direction of the spin density vector is closely related to the Gouy phase difference between longitudinal and transverse electric field component of the vectorial beam.

Projector distortion correction in 3D shape measurement using structured-light system by deep neural networks

SHENZHEN LV, Qiang Sun, Yuyuan Zhang, Yang Jiang, JIANBAI YANG, Jian LIU, and Jian Wang

Doc ID: 383338 Received 15 Nov 2019; Accepted 21 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: In structured light system, lens distortion of the camera and projector is the main source of 3D measurement error. In this letter a new approach of using deep neural networks to address this problem is proposed. The neural network is with one input layer, five densely-connected hidden layers and one output layer. A ceramic plate with flatness less than 0.005 mm is used to acquire the training, validation and test data sets for the network. It is shown that the measurement accuracy can be enhanced to 0.0165 mm in RMS value by this technique, which is an improvement of 93.52%. It is also verified that the constructed neural network is with strong robustness.

Bond additivity model for anisotropic second harmonic generation from two-dimensional honeycomb lattices

Weitao Liu, Fanjin Lu, Zeyuan Sun, and Shiwei Wu

Doc ID: 380452 Received 15 Oct 2019; Accepted 21 Nov 2019; Posted 02 Dec 2019  View: PDF

Abstract: We provide an analytical method for extracting detailed structural information about two-dimensional (2D) honeycomb lattices from the optical second harmonic generation (SHG) anisotropy patterns. When the lattice deviates from the ideal honeycomb structure, we relates the microscopic structural properties, such as bond length and bonding angle, to the macroscopic nonlinear susceptibility tensor based on the molecular bond additivity model. Our method shall help quantitative studies of 2D materials with SHG, and is readily applied to more general cases.

High conversion efficiency second-harmonic beam shaping via amplitude-type nonlinear photonic crystals

Bing Zhu, Haigang Liu, Yuping Chen, and Xianfeng Chen

Doc ID: 382108 Received 31 Oct 2019; Accepted 20 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: An efficient two-dimensional arbitrary harmonic wavefront shaping has been demonstrated in amplitude-type nonlinear photonic crystals, where the phase-matching condition is fulfilled through the birefringence and nonlinear Raman-Nath effect in longitudinal and transverse phase matching, respectively. The binary modulated nonlinear photonic crystal was fabricated by femtosecond laser micromachining based on binary computer-generated holograms. Three second-harmonic Hermite-Gaussian beams: HG10, HG11, and HG12 have been achieved by pumping a nanosecond pulsed fundamental Gaussian beam, with the measured normalized conversion efficiency of 8.4% W-1 cm-2 in the first diffraction order of the HG11 structure. The amplitude-type nonlinear photonic crystal opens wide possibilities in the field of efficient harmonic beam shaping and mode conversion.

Generation of 14.0 W of single frequency light at 770 nm by intracavity frequency doubling

Minho Kwon, Peiyu Yang, Preston Huft, Christopher Young, Matthew Ebert, and Mark Saffman

Doc ID: 374941 Received 03 Sep 2019; Accepted 20 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: We present a continuous, narrow-linewidth, tunable laser system that outputs up to 14.0 W at 770 nm. The light is generated by frequency doubling 18.8 W of light from a 1540 nm fiber amplifier that is seeded by a single mode diode laser achieving >74% conversion efficiency. We utilize a Lithium Triborate Crystal in an enhancement ring cavity. The low intensity noise and narrow linewidth of the 770 nm output are suitable for cold atom experiments.

An enhanced fully optically-pumped magnetic resonance with the optical sideband auxiliary pumping

Zhiyuan Jiang, Xiaochi Liu, Pingwei Lin, Jifeng Qu, and H. P. Liu

Doc ID: 378311 Received 20 Sep 2019; Accepted 20 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: We have proposed a new technique to obtain highly polarized atoms for improving the sensitivity of the all-optical Cs atomic magnetometer. In a Bell-Bloom magnetometer, the resonance pumping between the ground state Fg =3 to the excited state Fe =4 at D1 line can be used to polarize the Cs atoms and depopulate the sublevels of the | Fg=4, mF=4> partly. We utilize a modulation technique to generate a sideband frequency which serves to complement the leaking transition Fg=4 → Fe=3 and to drive more atoms to the target state | Fg=4, mF=4>. This improvement significantly increases the magnetic resonance and has little effect on the linewidth of resonance. It is very suitable for the miniature of the atomic magnetometer in the future.

Generation and characterization of burst modes in passively mode-locked lasers with internal Fabry-Perot cavities

Shu-Ching Li, Tzu-Lin Huang, Y. H. Hsieh, Hsing-Chih Liang, K. F. Huang, and Yung-Fu Chen

Doc ID: 378429 Received 20 Sep 2019; Accepted 20 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: The generation of burst pulses in a multi-pass passively mode-locked laser is systematically explored. We exploit intracavity mirrors with different thickness to serve as reflected Fabry-Perot (RFP) cavities in laser resonators. With the thinnest optical thickness of RFP cavity, we can generate picosecond optical burst pulses with the highest intra-burst pulse rate of 33.12 GHz. The maximum output power of 2.6 W is obtained at an incident pump power of 11.9 W. We further develop an analytical model which considers the RFP effects to manifest the first-order autocorrelation and spectral behaviors in experiments. The agreement between theoretical analyses and experimental explorations provides the feasibility to flexibly manipulate the burst modes in practical applications.

Multiphoton absorption in type-II InAs/GaSb superlattice structure

Chengcheng Zhao, Jianliang Huang, Biyin Nie, jinchuan zhang, Yanhua Zhang, and Wenquan Ma

Doc ID: 378481 Received 25 Sep 2019; Accepted 20 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: We report on multiphoton absorption of a type II superlattice (T2SL) infrared photodetector using InAs/GaSb materials. At 87 K, the 100% cut-off wavelength of the detector response is 3.4 μm for linear absorption, however, we have observed degenerate two and higher multiphoton absorptions using a quantum cascade laser (QCL) (λ=4.6 μm) as the excitation source. The observed photocurrent responses are designated as due to 2-photon, 5-photon and 11-photon absorption (2PA, 5PA, and 11PA) for different incident laser power ranges. Considering the wide detection wavelength range covered, which extends from 1 to 30 μm, this result may demonstrate unlimited potential for research and applications based on multiphoton absorption using InAs/GaSb T2SL materials.

Dual Frequency Comb Assisted Analog-to-Digital Conversion

Callum Deakin and Zhixin Liu

Doc ID: 381099 Received 21 Oct 2019; Accepted 19 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: Photonic analog to digital conversion offers promise to overcome the signal-to-noise ratio (SNR) and sample rate trade-off in conventional analog to digital converters (ADCs), critical for modern digital communications and signal analysis. We propose using phase-stable dual frequency combs with a fixed frequency spacing offset to downconvert spectral slices of a broadband signal and enable high resolution parallel digitization. To prove the concept of our proposed method, we demonstrate the detection of a 10-GHz subcarrier modulated (SCM) signal using 500-MHz bandwidth ADCs by optically converting the SCM signal to ten 1-GHz bandwidth signals that can be processed in parallel for full signal detection and reconstruction. Using sinusoidal wave based standard ADC testing, we demonstrate a spurious-free dynamic range (SFDR) of >45dB and signal-to-noise-and-distortion (SINAD) of >20dB, limited by the receiver front-end design.

Vortex γ-rays from scattering laser bullets off ultrarelativistic electrons

Yang-Yang Liu, Yousef Salamin, Zhen-Ke Dou, Zhongfeng xu, and Jianxing Li

Doc ID: 383312 Received 14 Nov 2019; Accepted 19 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: Generation of high-flux vortex γ-ray pulses is investigated in the interaction of ultraintense Bessel-Bessel laser bullets colliding head-on with ultrarelativistic electron bunches, in the quantum radiation-dominated regime. In the simulations a semiclassical Mont-Carlo method is used, based on the radiation probabilities in the local constant field approximation, to describe the electron motion and emission of radiation. Characteristics of the driving laser pulse (orbital angular momentum and nondiffracting spatial and temporal structures) are transferred to the emitted γ-rays, by nonlinear Compton scattering. The scheme is shown to be robust with respect to the laser and electron parameters.

Polarization-independent plasmonic absorption in stacked anisotropic 2D material nanostructures

Sheng-Xuan Xia, Xiang Zhai, Lingling Wang, and Shuangchun Wen

Doc ID: 382649 Received 07 Nov 2019; Accepted 18 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: Here we study the possibility to achieve polarization-independent optical absorption in stacked anisotropic 2D material nanostructures (NSs). Focusing on black phosphorus (BP), we demonstrate that by crossly stacking even-layered NSs, surface plasmons resonant in the two lattice directions are complementally excited, leading to polarization-independent absorption at any layer distance. This property is numerically validated using full electromagnetic simulations and theoretically predicted by a two-particle model. Our propose can open up the possibility of anisotropic 2D materials to develop polarization-independent plasmon devices like sensors and absorbers.

Dual-wavelength injection-seeded Q-switched Ho: YLF laser for CO2 DIAL application

Yunpeng Wang, Tongyu Dai, Xinyu Liu, Youlun Ju, and Baoquan Yao

DOI: 10.1364/OL.44.006049 Received 31 Oct 2019; Accepted 18 Nov 2019; Posted 19 Nov 2019  View: PDF

Abstract: A dual-wavelength injection-seeded Q-switched Ho: YLF laser for CO2 differential absorption lidar (DIAL) pumped by thulium-doped fiber laser was demonstrated. The single-frequency Ho: YLF seed laser was achieved by a pair of highly anti-misalignment corner cubes. The wavelength of on-line seed laser was corrected to the P12 CO2 absorption line at 2064.414 nm by using a CO2 absorption cell. At the pulse repetition frequency (PRF) of 100 Hz, the single-frequency pulsed energy was 16.1 mJ with a pulse width of 221.3 ns after a single-pass amplifier. The full width at half maximum (FWHM) of single-frequency pulsed spectrum was about 3.87 MHz, and the fluctuation of center frequency was 2.8 MHz in 30 minutes.

Complex degree of coherence and fringe visibility in spatial unitary transformations of scalar fields

Atri Halder and Ari Tapio Friberg

Doc ID: 379237 Received 01 Oct 2019; Accepted 18 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: We study the effects of spatial unitary transformations on the complex degree of coherence and the visibility of intensity fringes in Young's double pinhole interference setup with scalar optical fields. We demonstrate that the degree of coherence and the visibility, in general, change in the transformation and may become zero for the output beams even when the input beams are correlated. Moreover, we explore the influence of spatial unitary transformations on the complementarity relations associated with the degree of coherence, the intensity distinguishability, and the concurrence. We illustrate the results with the help of Gaussian Schell-model beams. Nonabsorbing beam splitters, which are key elements in optical systems, are practical realizations of spatial unitary transformations.

Anomalous Plasmon Hybridization in Nanoantennas near Interfaces

Jingxuan Wei and Chengkuo Lee

DOI: 10.1364/OL.44.006041 Received 22 Oct 2019; Accepted 18 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: We report an anomalous plasmon hybridization in side-by-side coupled metallic nanoantennas on top of silicon waveguide. In contrary to the conventional perception based on Coulomb coupling, the hybridized anti-symmetric mode in our structure possesses a higher resonance frequency than the symmetric mode. This unusual phenomenon reveals a new mechanism of plasmon hybridization, namely, coupling induced charge redistribution (CICR). Our work includes numerical simulation, experimental validation and theoretical analysis, emphasizing the importance of dielectric interfaces in coupled plasmonic structures, and offers new possibilities for non-Hermitian systems and integrated devices.

Thin-film tunable bandpass filter for spectral shift detection in surface plasmon resonance sensors


Doc ID: 377845 Received 13 Sep 2019; Accepted 18 Nov 2019; Posted 19 Nov 2019  View: PDF

Abstract: This study proposes the use of a thin-film tunable band-pass filter (TTBF) as an accurate absorption spectral shift detector in surface plasmon resonance (SPR) sensors. Passband central wavelength of the TTBF can be tuned by changing the incident angle. A single TTBF is required to filter two passband with central wavelengths on the falling and rising curves of the SPR absorption spectrum. The spectral shift can then be converted to the differential intensity change of these two TTBF output beams using the differential detectors to eliminate the common-mode noise. This method can perform a high resolution sensing for the refractive index change in the SPR sensor surface without using high-performance spectrometers. A grating-coupled SPR sensor was used in the experiment system, and achieved a detection resolution of 6.99×10E-6 RIU.

Ultrafast-laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH4 in flames

Ryan Tancin, Ziqiao Chang, Mingming Gu, Vishnu Radhakrishna, Robert Lucht, and Christopher Goldenstein

Doc ID: 380091 Received 14 Oct 2019; Accepted 18 Nov 2019; Posted 19 Nov 2019  View: PDF

Abstract: This Letter describes the development of an ultrafast (i.e., femtosecond), mid-infrared, laser-absorption diagnostic and its initial application to measuring temperature, CO and CH4 in flames. The diagnostic employs a Ti:Sapphire oscillator emitting 55-fs pulses near 800 nm which were amplified and converted into the mid-infrared (mid-IR) though optical parametric amplification (OPA) at a repetition rate of 5 kHz. The pulses were directed through the test gas and into a high-speed mid-infrared spectrograph to image spectra across a ≈30 nm bandwidth with a spectral resolution of ≈0.3 nm. Gas properties were determined by least-squares fitting a spectroscopic model to measured single-shot absorbance spectra. The diagnostic was validated with measurements of temperature, CO, and CH4 in a static-gas cell with an accuracy of 0.7% to 1.8% of known values. Single-shot, 5 kHz measurements of temperature and CO were acquired near 4.9 μm in a laser-ignited HMX (i.e., 1,3,5,7-tetranitro-1,3,5,7-tetrazocane) flame and exhibited a 1-σ precision of 0.4% at ≈2700 K. Further, CH4 and temperature measurements were acquired near 3.3μm in a partially premixed CH4-air flame produced by a Hencken burner and exhibited a precision of 0.3% at ≈1000 K.

17.9 W continous-wave self-frequency-doubled Nd:GdCOB laser

Haohai Yu, Jinheng Du, jiyang wang, and Huaijin Zhang

Doc ID: 380340 Received 15 Oct 2019; Accepted 18 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: We demonstrated the output power scaling of a self-frequency-doubled (SFD) laser with Nd:GdCa4O(BO3)3 (Nd:GdCOB) crystal by employing a partially end-pumped slab structure and optimized laser-diode (LD) pump wavelength. Associated with the theoretical calculation about the thermal distribution in the SFD Nd:GdCOB crystal, the maximum SFD output power was achieved to be 17.91 W at the wavelength of 545.5 nm, which represents the highest output power in SFD lasers and the optical conversion efficiency from the LD to SFD laser power reached up to 20%. Since the wavelength at 545.5 nm is located at the eye-sensitive spectral region and the SFD lasers have the advantages in the compact structure, the present SFD laser should have promising applications in some regimes such as laser display, medical, military, scientific research, etc.

Terahertz tunable filter and modulator based on magneto plasmon in transverse magnetized InSb

Tengfei Li, Fei Fan, Yun-Yun Ji, zhiyu tan, Qianyi Mu, and Shengjiang Chang

Doc ID: 379923 Received 07 Oct 2019; Accepted 17 Nov 2019; Posted 25 Nov 2019  View: PDF

Abstract: Transverse magneto-optical (MO) effect of InSb has been theoretically and experimentally investigated in the terahertz (THz) regime. The calculated photonic band structure and experimental measurements show that a unique circularly polarized magneto plasmon mode and a linear polarized transverse magnetic mode can be sensitively manipulated by a weak magnetic field. Moreover, these results indicate that the transverse magnetized InSb can be used as a THz tunable high pass filter and a MO modulator. The cut-off frequency of filter can be broadly tuned from 0.4 to 0.8 THz when the magnetic field changes from 0 to 0.22 T, and the modulation depth of 20dB can be obtained in 0.2~0.5 THz band. This research has significance for the deep understanding to THz MO effect of InSb and promotes the development of THz MO devices.

3D Holographic light Shaping for AdvancedMultiphoton Polymerization

MARIA MANOUSIDAKI, Dimitris Papazoglou, Maria Farsari, and Stelios Tzortzakis

Doc ID: 381012 Received 22 Oct 2019; Accepted 17 Nov 2019; Posted 19 Nov 2019  View: PDF

Abstract: A three-dimensional holographic focal volumeengineering method is proposed and employed foradvanced Multiphoton Polymerization. A bundle of pointsources are precisely positioned in space according to adesigned geometry and through all-optical microdisplacementin space they lead to the realization ofcomplete 3D arbitrary structures. The microstructuresare fabricated by Direct Laser Writing without additionaloptical or mechanical motion support, while the methodprovides 20-times faster fabrication time in comparisonto point-by-point laser polymerization techniques.

Multiplexed confocal microscope with a refraction array scanner and SPAD array detector

Nehad Hirmiz, Anthony Tsikouras, Elizabeth Osterlund, Morgan Richards, David Andrews, and Qiyin Fang

Doc ID: 379916 Received 23 Oct 2019; Accepted 17 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: Currently, the spinning disk confocal microscope is the most popular fast confocal imaging system. However, these instruments require a high pixel density camera detector, limiting their use in many applications. We have designed a multiplexed confocal scheme that performs raster scanning of a 32x32 foci array in which the output image is stationary after de-scanning. Our system can be coupled to a dense or sparse array detector, making it feasible to to rapid time-resolved photon counting, single-photon detection, and apply to some super-resolution techniques.

PbS nanoparticles saturable absorber for ultrashort pulse generation in the 2-um regime

Xinxing Liu, Xiaohui Li, Yulong Tang, and Shuaiyi Zhang

Doc ID: 376192 Received 23 Aug 2019; Accepted 17 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: Lead sulfide (PbS) has unique electronic and optical properties (e.g., narrow bandgap of ~0.4 eV), and has stimulated great interest in broadband ultrafast optics. Here, PbS nanoparticles (NPs) deposited on a gold mirror is used as saturable absorber (SA) to modulate a 2 μm Tm-doped fiber laser for ultrafast pulse generation. The PbS NPs have a broadband linear absorption decreasing from 350 nm to 2400 nm, with an absorption coefficient of >20% at 2 μm. Nonlinear optical absorption of the PbS NPs SA at 2 μm was also measured, giving a modulation depth of 8.8% and a saturable intensity of 0.8 MW/cm2. The stable mode-locked Tm-doped fiber laser with the PbS NPs SA gives maximum pulse energy of 7.3 nJ, pulse width of 4.24 ps, spectral width of 2.5 nm at ~1993 nm, and repetition rate of 15.9 MHz. Our works indicate that PbS NPs are good candidates as light modulators in the 2-μm mid-infrared region, and thus can find great applications for integrated optoelectronics.

Linewidth-narrowing of a continuous wave terahertz polariton laser using an intracavity etalon

Yameng Zheng, Andrew Lee, David Spence, and Helen Pask

Doc ID: 377585 Received 12 Sep 2019; Accepted 17 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: An uncoated etalon was incorporated within an intracavity CW terahertz polariton laser, leading to a ten-fold reduction in linewidth, plus a factor of two increase in the THz output power. The increase in output power is explained in terms of phase-matching considerations for the parametric down-conversion process.

Generation of terahertz radiation in dielectric-metal structure irradiated by femtosecond laser pulse.

Sergey Uryupin and Vyacheslav Grishkov

Doc ID: 378531 Received 23 Sep 2019; Accepted 17 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: The generation efficiency of THz radiation in the skin layer of the metal increases significantly when a nanolayer of dielectric is deposited on the metal surface. Additional amplification of the generation occurs if a weakly focused femtosecond pulse affects a structure where electron collision frequency in the metal greater than inverse duration of the pulse.

Luminescence lifetime imaging using cellphone camera with electronic rolling shutter

Bo Xiong and Qiyin Fang

Doc ID: 381137 Received 24 Oct 2019; Accepted 17 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: Luminescence lifetime imaging systems are typically complex and expensive instruments targeting bench-top applications. We present a low-cost approach for video frame rate luminescence lifetime imaging on the microsecond scale based on a cellphone camera. The luminescence lifetime is mapped by measuring the phase shift of optical fringes captured by a camera with an electronic rolling shutter at 30 frames per second. Luminescence lifetime imaging is validated by observing a PtTFPP/polystyrene film with a non-uniform lifetime distribution. Experimental results indicate a lifetime resolution of 580 ns when a lifetime of 22 s is measured. This device is portable, low-cost, and shows the potential in point-of-care diagnostic and environment applications that measure long lifetime luminescence.

Broadband amplitude and frequency demultiplexer for terahertz frequencies using parallel-plate-waveguides technology

Arturo Hernandez, Daniel Mittleman, and Emma Pickwell-MacPherson

Doc ID: 379411 Received 07 Oct 2019; Accepted 17 Nov 2019; Posted 22 Nov 2019  View: PDF

Abstract: In this work we report a novel broadband frequency/polarization demultiplexer based on parallel-plates-waveguides (PPWG) for terahertz (THz) frequencies. The fabrication and experimental validation of this polarization sensitive demultiplexer is demonstrated for the range from 0.2 THz to 1 THz. By adding a second demultiplexer stage, a fifty-fifty amplitude splitter is also demonstrated in the same frequency range. The multiplexer is based on a traveling-wave antenna, exhibiting strong mechanical robustness. This unique device exhibits three splitting mechanisms in the same device; amplitude, polarization and frequency splitting. This is a significant improvement for the next generation of THz passive components for communication purposes.

Correlated random bit generation based on common-signal-induced synchronization of wideband complex physical entropy sources

Ning Jiang, Anke Zhao, Yajun Wang, Shiqin Liu, Baochuan Li, and Kun Qiu

Doc ID: 378775 Received 25 Sep 2019; Accepted 16 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: We propose and experimentally demonstrate a novel correlated random bit generation (CRBG) scheme, in virtue of the synchronization of two physical entropy sources that are composed of a continuous-wave (CW) laser, a phase modulator (PM) that is driven by the output of a local laser subject to constant-amplitude and random-phase (CARP) injection, as well as a dispersive component. It is experimentally indicated that, wideband complex physical entropy sources with an effective bandwidth of 22 GHz can be achieved, and also, high-quality synchronization with a large cross-correlation coefficient (~0.95) can be achieved by introducing symmetric CARP injections into the local lasers at Alice and Bob ends. Based on this, two distributed correlated random bit sequences (CRBSs) with a bit rate over 3 Gb/s and satisfactory consistency are independently generated at Alice and Bob ends, the excellent randomness of CRBSs is verified using a test suite of the National Institute of Standards and Technology (NIST).

Trace gas sensing using diode-pumped collinearly-detected spontaneous Raman scattering enhanced by a multipass cell

Juan Gomez Velez and Andreas Muller

Doc ID: 375893 Received 19 Sep 2019; Accepted 15 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: A simple but highly effective method for enhancement of spontaneous Raman scattering from gases is described. It employs a multimode blue laser diode which receives feedback from a near concentric bidirectional multi-pass cavity in such a way as to generate a circulating power of order 100 W for a sample volume of 10 mm³. The feedback, provided via a volume Bragg grating, reduces the laser bandwidth to 4 wavenumbers. Spectra of spontaneous Raman scattering from ambient atmospheric air, detected collinearly with the pump, were recorded with a limit of detection below 1 part-per-million. The performance of the setup is further illustrated through detection of acetone, methane,and isotopic carbon dioxide in breath.

Optimal design for spectral narrowing and fast frequency sweep of an interferometer-stabilized laser

Ashby Hilton, Philip Light, Lauris Talbot, and Andre Luiten

Doc ID: 381184 Received 24 Oct 2019; Accepted 14 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: Self-heterodyne fiber interferometers have been shown to be capable of stabilizing lasers to ultra-narrow linewidths and present an excellent alternative to high finesse cavities for frequency stabilization.In addition to suppressing frequency noise, these devices are highly tunable, and can be manipulated to produce high speed frequency sweeps over the entire range of the laser.We present an analytic approach for choosing a delay-line length for both optimal noise suppression and highest in-loop frequency sweep rate.Based on this model we stabilize an extended cavity diode laser to a fiber Michelson interferometer and demonstrate a linewidth of 700 Hz over millisecond timescales while also allowing for a frequency scan rate of 1 TH/z.We independently measure the maximum deviation from linearity of the sweep to be only 100kHz.

Carbon nanotube Q-switched Yb:KLuW surface channel waveguide lasers

Ji Bae, TAE GWAN PARK, Esrom Kifle, Xavier Mateos, Magdalena Aguilo, Francesc Diaz, Carolina Romero, Javier Vazquez de Aldana, Hansuek Lee, and Fabian Rotermund

Doc ID: 378820 Received 26 Sep 2019; Accepted 14 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: A channel waveguide buried immediately below the surface of a Yb:KLuW crystal is used as a laser gain medium for passive Q-switching by both evanescent- and direct-field interactions using single-walled carbon nanotubes (SWCNTs) near 1040 nm. The SWCNTs used as saturable absorbers (SAs) are deposited on top of the half-ring-type channel waveguide fabricated via femtosecond direct laser writing. The Q-switched waveguide laser delivers 88.5-ns pulses at a 1.16-MHz repetition rate with a maximum average output power of 680 mW. For the two different interaction schemes with SWCNT-SAs, the pulse characteristics depending on the output coupling ratio and absorbed pump power are experimentally investigated and compared to the results of theoretical analysis of the SA Q-switched operation.

Mode-locked and tunable fiber laser at the 3.5 µm band using frequency-shifted feedback

Ori Henderson-Sapir, Nathaniel Bawden, Matthew Majewski, Robert Woodward, David Ottaway, and Stuart Jackson

Doc ID: 378486 Received 23 Sep 2019; Accepted 14 Nov 2019; Posted 21 Nov 2019  View: PDF

Abstract: We report on a mid-infrared mode-locked fiber laser that uses an acousto-optic tunable filter to achieve frequency-shifted feedback pulse generation with frequency tuning over a 215 nm range. The laser operates on the 3.5 µm transition in erbium-doped zirconium fluoride-based fiber and utilizes the dual-wavelength pumping scheme. Stable, self-starting mode-locking with a minimum pulse duration of 53 ps was measured using a two-photon absorption autocorrelator. The longest wavelength demonstrated was 3612 nm and a maximum average power of 208 mW was achieved. This is the longest wavelength rare-earth doped mode-locked fiber laser demonstrated to the best of the authors’ knowledge. The broad tunability promises potential uses for environmental sensing applications.

BGD-based Adam algorithm for time-domain equalizer in PAM-based optical interconnects

Ji Zhou, Haide Wang, Weiping Liu, Jianping Li, xincheng huang, Long Liu, Weixian Liang, Changyuan Yu, Fan Li, and Zhaohui Li

Doc ID: 380550 Received 17 Oct 2019; Accepted 14 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: To the best of our knowledge, for the first time, we propose adaptive moment estimation (Adam) algorithm based on batch gradient descent (BGD) to design a time-domain equalizer (TDE) for PAM-based optical interconnects. Adam algorithm has been widely applied in the fields of artificial intelligence. For TDE, BGD-based Adam algorithm can obtain globally optimal tap coefficients without being trapped in locally optimal tap coefficients. Therefore, fast and stable convergence can be achieved by BGD-based Adam algorithm with low mean square error. Meanwhile, BGD-based Adam algorithm is implemented by parallel processing, which is more efficient than conventional serial algorithms, such as least mean square and recursive least square algorithms. The experimental results demonstrate that BGD-based Adam feed-forward equalizer works well in 120-Gbit/s PAM8 optical interconnects. In conclusion, BGD-based Adam algorithm shows great potential for converging the tap coefficients of TDE in future optical interconnects.

Development of high luminous efficacy red-emitting phosphor in glass (PiG) for high-power LED lighting system using our original low Tg and Ts glass

Sun Woog Kim, Young Ji Park, Gyu Jin Jeong, Jin-Ho Kim, Young Jin Lee, Cheol Jin Kim, and Jonghee Hwang

Doc ID: 378364 Received 20 Sep 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: Red-emitting PiG materials with a high luminescence efficiency were developed by co-firing commercial red-emitting (Sr,Ca)AlSiN3:Eu2+ (SCASN) phosphor and our original glass frits with composition of Li2O-Na2O-ZnO-Al2O3-B2O3-P2O5, which has a low Tg (271 °C) and Ts (380 °C) temperatures. By optimizing the sintering temperature and the content of the phosphor, the highest luminous efficacy was obtained for the 3 wt% SCASN-based PiG sintered at 400 °C, which showed a luminous efficacy of 25 lm/Wrad by combining the PiG materials with a blue LED chip-on-board (COB; incident power = 100 mA). The internal quantum efficiency of this sample under excitation at 450 nm was 53%. The PiG-based LED maintained a high luminous efficacy when incident power of the blue COB increased up to 5.5W (47 lm).

Optical damage thresholds of microstructures made by laser 3D nanolithography

Agnė Butkutė, Laurynas Čekanavičius, Gabrielius Rimšelis, Darius Gaulevičius, Vygantas Mizeikis, Andrius Melninkaitis, Tommaso Baldacchini, Linas Jonusauskas, and Mangirdas Malinauskas

Doc ID: 378915 Received 26 Sep 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: Direct laser writing based on non-linear 3D nanolithography (also known as 3D laser lithography, 3DLL) is a powerful technology to manufacture polymeric micro-optical components. However, practical applications of these elements are limited due to the lack of knowledge of their optical resilience and durability. In this work, we employ 3DLL for the fabrication of bulk (i.e. fully filled) and woodpile structures out of different photopolymers. We then characterize them using S-on-1 laser induced damage threshold (LIDT) measurements. In this way, quantitative data of LIDT values can be collected. Furthermore, this method permits to gather damage morphologies. The results presented in this work demonstrate that LIDT values depend on the material and the geometry of the structure. Bulk non-photosensitized hybrid organic-inorganic photopolymer SZ2080 structures are found to be the most resilient with a damage threshold being of 169±15 mJ/cm2.

Engineering colors in all-dielectric metasurfaces: metamodeling approach

Alma González-Alcalde, Rafael Salas-Montiel, Victor Kalt, Sylvain Blaize, and Demetrio Macias

Doc ID: 379704 Received 07 Oct 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: In this letter, we engineer the colors of all-dielectric metasurfaces by means of a meta-model based optimization approach. This algorithm combines heuristic optimization and neural networks to retrieve the metasurface's optimal geometrical parameters that serve to reproduce a prescribed color. The metasurfaces were fabricated and experimentally validated through dark field optical microscope images. We present typical results for periodic arrays of nanoparticles with arbitrary cross section. The approach is well-suited for color reproduction and computationally inexpensive.

1030-nm passively Q-switched Yb-doped fiber laser using excited-state absorption of thulium fiber

Tzong-Yow Tsai and Zhi-Cheng Lee

Doc ID: 381946 Received 29 Oct 2019; Accepted 14 Nov 2019; Posted 15 Nov 2019  View: PDF

Abstract: We demonstrated a pulsed ytterbium all-fiber laser passively Q-switched using excited-state absorption of thulium fiber and mode-field-area mismatch. The absorption cross section of the excited state 3F4 was measured and determined to be the key factor inducing pulsing, and it was much higher than that of the ground state 3H6 over 0.95 to 1.15 μm. By successfully realizing the pulsed laser at 1030 nm, which is the most critical wavelength for Q-switching, we verified that the excite state 3F4 of Tm3+ could be a full-range saturable-absorber Q-switch for a Yb fiber laser over 1.0 to 1.15 μm.

Three-dimensional micropatterning of graphene by the femtosecond laser direct writing technology

Yu-Qing Liu, Jiang-Wei Mao, Zhao-Di Chen, Dong-Dong Han, Zhi-Zhen Jiao, Jia-Nan Ma, Hao-Bo Jiang, and Han Yang

Doc ID: 374402 Received 31 Jul 2019; Accepted 14 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: The reduction and patterning of graphene oxides (GO) have abroad applications in gene transfection, cell differentiation control, and etc. However, two-dimensional (2D) photoreduction technologies (such as: UV lithography) failed to realize the three-dimensional (3D) reduction and patterning of GO, limiting its applications in three-dimensional electronic device interconnection and three-dimensional graphene organ-on-a-chip. Here, we developed 3D reduction and patterning of GO by femtosecond laser direct writing (FsLDW) technology. FsLDW has adopted for 3D structure nanofabrication and 2D/3D micropatterning of reduced graphene oxides (RGO) on GO film. We deem that this technology will advance GO in the evolution of future electronics.

Interconversion of orbital and spin angular momentum of light beams in sum-frequency generation process from the surface of isotropic chiral medium

Kirill Grigoriev, Vladislav Diukov, and Vladimir Makarov

Doc ID: 379023 Received 02 Oct 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We study the interaction between spin and orbital components of the angular momentum of the electromagnetic waves in the sum-frequency generation process at reflection from a surface of the nonlinear isotopic chiral medium. Both bulk and near-surface response of the medium are taken into account. Classical and quantum explanation of particular features of three-wave mixing on the surface of nonlinear medium are presented.

Time-resolved investigation of the optical phase change as a potential diagnostics tool for XUV FEL pump - optical probe experiments

Victor Tkachenko, Sven Toleikis, Vladimir Lipp, Beata Ziaja, and Ulrich Teubner

Doc ID: 380271 Received 23 Oct 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: Measurement of transient optical properties (reflectivity and transmissivity) is widely performed in extreme ultraviolet (XUV) pump - optical probe experiments to study the transient state of irradiated materials. In order to extend the material diagnostics, here we propose an additional measurement of the transient phase change of the optical probe pulse. It can be recorded in parallel to other transient optical properties, enabling access to the full information on the refractive index and the thickness of the radiation-modified material layer. The latter is essential for investigations of phase transitions progressing in XUV (and X-ray) irradiated materials. We perform a computational study that clearly shows that the measurement of the optical phase from a probe pulse at correctly tuned pulse parameters can provide a signal strong enough to extract information on transient material properties. The calculations suggest that in some cases it is even more preferable to measure the transient phase change than other optical parameters. Such phase measurement, feasible with modern experimental setups, can then be a basis for an improved diagnostic tool for the temporal characteristics of an ultrashort XUV pulse.

Cross-sectional refractive-index variations in fiber Bragg gratings measured by quantitative phase imaging

Grayson Noah, Yijun Bao, and Thomas Gaylord

Doc ID: 377794 Received 13 Sep 2019; Accepted 12 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: Unexpected micron-scale patterns in the induced refractive index of various commercial fiber Bragg gratings (FBGs) are observed in the cross-sectional fiber directions which are in addition to the expected periodic variations along the fiber axis. These measurements were made using 3D tomographic deconvolution phase microscopy (TDPM), a type of quantitative phase imaging (QPI). The cross-sectional patterns observed are shown to exhibit a variety of appearances including fringes normal to the fiber axis and radial blades, the details apparently depending on the FBG writing method. Such patterns appear to be due to the interaction of the locally inhomogeneous structure of the Ge-doped glass with the high-intensity exposure light.

Kink-based mirrorless quasi-bistability in resonantly absorbing media

Denis Novitsky and Alexander Shalin

Doc ID: 378802 Received 25 Sep 2019; Accepted 12 Nov 2019; Posted 13 Nov 2019  View: PDF

Abstract: Optical bistability, the basic nonlinear phenomenon mediating the control of light by light, paves the way to the all-optical logic being of ultimate demand for a plethora of applications in laser information technologies. The desirable features of the optically bistable elements are low power consumption, speed of switching and small size. The two most general designs are driven by the presence or absence of an external feedback giving rise to a variety of possible setups. Among them, mirrorless architecture seems promising being free of bulky mirrors, resonant cavities, photonic crystals, etc. In this paper, we propose a novel method to achieve optical quasi-bistability governed by the formation of specific nonlinear waveforms called ``kinks'. We show that a thin layer of the relatively dilute resonant medium specially designed to support kinks could serve as a platform for compact, ultra-fast, low power optical switching. This new physical mechanism do not require high densities of resonant particles specific for other feedback-free devices driven by local field corrections and dipole-dipole interactions, and enhance the overall practical relevance of such devices for optical computing.

Compact terahertz spectrometer based on sequential modulation of disordered rough surfaces

Tao Yang, Yue Zhang, Jiacheng Ge, Lei Wang, Yi-qiang QIN, Y Zhu, Wei Huang, and Ho-Pui Ho

Doc ID: 377509 Received 23 Sep 2019; Accepted 12 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We present herein a compact THz spectrometer in which transmission intensity distribution associated with dispersive interference effects in disordered random surfaces are used for reconstructing the frequency contents of an incoming THz beam. The device sweeps the frequency-dependent parameter of a roughened transmission plate through lateral displacement or electro-optic modulation. 2-D transmission intensities are sequentially captured by a single detector for a range of modulation depths. With a calibration data set as the reference, one can reconstruct the spectra of the probe terahertz beam by solving a system of simultaneous linear equations. A smoothing Tikhonov regularization approach has been implemented to improve the accuracy of the spectral reconstruction. The reported compact, broadband, high-resolution terahertz spectrometer is well suited for portable terahertz spectroscopy applications.

GaN/AlN quantum-disk nanorod 280 nm deep ultraviolet light emitting diodes by molecular beam epitaxy

tongbo wei, I. S. ISLAM, Uwe Jahn, jianchang Yan, Kevin Lee, Shyam Bharadwaj, xiaoli ji, junxi wang, jinmin li, Vladimir Protasenko, Huili (Grace) Xing, and Debdeep Jena

Doc ID: 371716 Received 04 Jul 2019; Accepted 12 Nov 2019; Posted 20 Nov 2019  View: PDF

Abstract: We report optically and electrically pumped ~280 nm deep ultraviolet (DUV) light emitting diodes (LEDs) with ultra-thin GaN/AlN quantum disks (QDs) inserted into AlGaN nanorods by selective epitaxial regrowth using molecular beam epitaxy (MBE). The GaN/AlN QD LED has shown strong DUV emission distribution on the ordered nanorods and high internal quantum efficiency of 81.2%, as a result of strain release and reduced density of threading dislocations revealed by TEM. Nanorod assembly suppresses the lateral guiding mode of light, and light extraction efficiency can be increased from 14.9% for planar DUV LED to 49.6% for nanorod DUV LED estimated by finite difference time domain simulations. The presented results offer the potential to solve the issue of external quantum efficiency limitation of DUV LED devices.

Iterative reconstruction for general linear imaging polarimetry without polarimetric calibration

Feng Han, Tingkui Mu, Donghao Bao, Abudusalamu Tuniyazi, Qiuxia Li, Hang Gong, Zeyu Chen, and Chunmin Zhang

Doc ID: 378633 Received 25 Sep 2019; Accepted 12 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: Usually, the practical analysis states of an imaging polarimeter must be calibrated, with a set of standard polarization states, for the accurate reconstruction of Stokes parameters. However, it is challenged to get the standard elements for the polarimetric calibration. In this letter, an iterative reconstruction method is presented at the first time to recover the polarization parameters from the data acquired by linear-Stokes polarimeters without polarimetric calibrations. Inspired from phase shifting interferometry, the method employs two least-squares iterative procedure and requires no any extra element for assistant. Experimental results show that the iterative method is more robust to noise perturbation and gets higher reconstruction accuracy compared to the traditional calibration method with reference polarization states.

High spectral purity photons generation from a dual-interferometer coupled silicon microring

Yingwen Liu, Chao Wu, Xiaowen Gu, yuechan kong, xinxin yu, Renyou Ge, Xinlun Cai, Xiaogang Qiang, Junjie Wu, xuejun yang, and Ping Xu

Doc ID: 376986 Received 26 Sep 2019; Accepted 11 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We experimentally demonstrate a high spectral purity photon source by designing a dual-Mach-Zehnder-interferometer coupled silicon ring resonator wherein the linewidths of pump and signal (idler) resonances can be engineered independently. A high spectral purity of 95%±1.5% is obtained via g² correlation measurement which exceeds the theoretical 93% bound of traditional ring's spontaneous four-wave mixing photon source. This source also possesses high performance in other metrics including a measured coincidence of 9599 pairs/s and a preparation heralding efficiency of 52.4% at a relatively low pump lower of 61 μW as well as a high drop-to-through suppression of 20.2 dB. By overcoming the trade-off between the spectral purity and brightness in the post-filtering way, such method guarantees the bright pure photons and will pave the development of on-chip quantum information processing with improved operation fidelity and efficiency.

100 µJ, 100 kHz, CEP-Stable High-Power Few-Cycle Fiber Laser

Evgeny Shestaev, D Hoff, A SAYLER, Arno Klenke, Steffen Hadrich, Florian Just, Tino Eidam, Péter Jójárt, Zoltan Várallyay, Karoly Osvay, Gerhard Paulus, Andreas Tünnermann, and Jens Limpert

Doc ID: 377169 Received 06 Sep 2019; Accepted 11 Nov 2019; Posted 14 Nov 2019  View: PDF

Abstract: We present a CEP-stable Yb-doped fiber laser system delivering 100 µJ few-cycle pulses at a repetition rate of 100 kHz. The CEP stability of the system when seeded by a CEO-locked oscillator is 360 mrad, as measured pulse-to-pulse with a Stereo-ATI phase meter. Slow CEP fluctuations have been suppressed by implementing a feedback loop from the phase meter to the pulse picking AOM. To the best of our knowledge, this is the highest CEP stability achieved to date with a fiber-based, high-power few-cycle laser.

Real-time transition dynamics between multi-pulsing states in a mode-locked fiber laser

Junjie Zeng and Michelle Sander

Doc ID: 377895 Received 02 Oct 2019; Accepted 10 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: We experimentally studied the transition dynamics between multi-pulsing states, specifically, the build-up and annihilation of soliton pulses between a double pulsing and a three-pulse state, utilizing the dispersive Fourier transform technique. The birth of an additional pulse in a mode-locked soliton fiber laser in a multi-pulsing regime arises from a dispersive wave that experiences strong intensity fluctuations while the other pulses maintain their shapes. During the decaying process to a double pulsing state, it is observed that all the pulses undergo a unique breathing behavior before settling into steady-state.

Orientation-dependent optic-fiber accelerometer based on excessively tilted fiber grating

Lang Xie, Bin-bin Luo, M Zhao, Ou Deng, Enhua Liu, Peng Liu, Yajie Wang, and Lin Zhang

Doc ID: 376562 Received 29 Aug 2019; Accepted 10 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: An orientation-dependent optic-fiber accelerometer based on the excessively tilted fiber grating (ExTFG) inscribed in SM28 fiber is demonstrated, which is based on the optical power demodulation scheme. Without any complicated processing, the cladding mode resonances of the bare ExTFG show high sensitivity to slight perturbation of the bending. Due to its excellent azimuth-related bending properties, such a bare ExTFG fixed on a simple cantilever beam has exhibited strong orientation-dependent vibration properties. Experiment results show that TE mode of the sensor can provide a maximal acceleration sensitivity of 74.14 mV/g@72 Hz and orientation sensitivity of 9.1 mV/deg, while for TM mode, it can provide a maximal acceleration sensitivity of 57.85 mV/g @72 Hz and orientation sensitivity of 7.4 mV/deg . These unique properties would enable the sensor acts as a vector accelerometer for the applications in the mechanical vibration measurement fields.

Dither-free stabilization of a femtosecond doubly-resonant OPO using parasitic sum-frequency mixing

Yuk Shan Cheng, Richard McCracken, and Derryck Reid

Doc ID: 378020 Received 13 Sep 2019; Accepted 09 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: Stable operation of a doubly-resonant femtosecond optical parametric oscillator (OPO) requires sub-micron matching of the OPO and pump-laser cavity lengths, which is normally implemented using a dither-locking feedback scheme. Here we show that parasitic sum-frequency-mixing between the pump and resonant pulses of a degenerate femtosecond OPO provides an error signal suitable for actuating the cavity length with the precision needed to maintain oscillation on a single fringe and at maximum output power. Unlike commonly used dither-locking approaches, the method introduces no modulation noise and requires no additional optical components, except for one narrowband filter. The scheme is demonstrated on a Ti:sapphire-pumped sub-40-fs PPKTP OPO, from which data are presented showing a tenfold reduction in relative intensity noise compared with dither locking.

Dense parallax images acquisition method using single-pixel imaging for integral photography

Tetsuhiko Muroi, Ren Usami, Teruyoshi Nobukawa, Masato Miura, Norihiko Ishii, and Eriko Watanabe

Doc ID: 377299 Received 09 Sep 2019; Accepted 09 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: In Integral photography, it is difficult to obtain three-dimensional photographs with high spatial resolution, high angular resolution, and a wide viewing angle, simultaneously. Thus, we proposed a dense parallax images acquisition method using single-pixel imaging. We confirmed that parallax images can be obtained depending on the position of the photo detector. By replacing the detector to each pixel of an image sensor, a two-dimensional image with different parallax in each pixel can be acquired. We demonstrated the reconstruction of dense parallax images according to the pixel position of the image sensor. This method is effective in addressing the trade-off among spatial resolution, angular resolution, and viewing angle. It can also improve the image quality in integral photography.

Frequency-agile injection-seeded terahertz-wave parametric generation

Yoshikiyo Moriguchi, Yu Tokizane, Yuma Takida, Kouji Nawata, Shigenori Nagano, Manabu Sato, Taiichi Otsuji, and Hiroaki Minamide

Doc ID: 376683 Received 30 Aug 2019; Accepted 08 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) enables access to low-frequency fingerprints of molecules in the THz frequency region. However, its conventional scan-rate is limited below 1 Hz. Thus, we propose an electrically controlled tuning system for the is-TPG, which provides high-speed scanning and random hopping agility. We achieved rapid THz frequency sweeping on a pulse-by-pulse basis by employing a gain-switched laser diode and a micro-electro-mechanical system tunable vertical-cavity surface-emitting laser as the pump and seed lasers. A THz spectrum was acquired with a ten times higher scan rate of 10 Hz for the 1–3 THz range with a frequency resolution of 4.6 GHz.

Reconstructing 3D point clouds in real time with look-up tables for structured light scanning still objects along both horizontal and vertical directions

Kai Liu, Jianwen Song, Daniel Lau, Xiujuan Zheng, Ce Zhu, and Xiaomei Yang

DOI: 10.1364/OL.44.006029 Received 26 Aug 2019; Accepted 08 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: By scanning still, not moving, objects along both the horizontal and vertical axes instead of one, structured light illumination achieves more accurate and robust 3D surface reconstructions but with greater latency on computing 3D point clouds. If scanning is performed along only one axis, it has been reported look-up tables, manually derived from the calibration matrices of a camera and a projector, can significantly help to speed up computation; however, it has been nearly impossible to manually derive similar look-up tables for phases scanned along two axes. In this Letter, we bridge this divide by introducing the constraint of epipolar geometry to automatically compute look-up tables and, thus, significantly speed up computing 3D point clouds only with basic arithmetic operations rather than time-consuming matrix computations. Experimental results show that the proposed method, only using single-thread CPU computing, reduces process latency by an order of magnitude.

Phase shifted modal interferometers for high accuracy optical fiber sensing

Joel Villatoro

Doc ID: 377351 Received 09 Sep 2019; Accepted 07 Nov 2019; Posted 11 Nov 2019  View: PDF

Abstract: The use of two separated, compact modal interferometers with an adequate phase shift is proposed for precision optical fiber sensing. The output spectrum of interferometers with such features is a well-defined peak. Changes in wavelength position or amplitude of said peak caused by a measurand can be detected with high precision. The advantages of phase-shifted interferometers for sensing include sensitivity enhancement, easy implementation, simple interrogation, and compactness, among others. The concept is demonstrated by placing two supermode interferometers in series that were built with multicore fiber to sense vibrations with low frequencies and low amplitudes. However, many other parameters can be sensed. The sensing architecture here proposed can also be implemented with other type of optical fiber interferometers and the advantages mentioned above can be achieved.

Constant intensity conical diffraction in discrete one-dimensional lattices with charge-conjugation symmetry

Mojgan Dehghani, Cem Yuce, Tsampikos Kottos, and Hamidreza Ramezani

Doc ID: 375589 Received 21 Aug 2019; Accepted 07 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We engineer anomalous conical diffraction (CD), occurring in discrete one-dimensional lattices with charge-conjugation symmetry when an exceptional point (EP) is in the proximity of the modes that compose the initial excitation. The evolving waveform propagates ballistically, acquiring a constant intensity profile within the boundaries of the spreading cone. The linear increase in the total intensity along the propagation direction is responsible for the generation of the constant intensity CD.

All-optical control of pattern dynamics generated by Airy beams

Lamyae Drouzi, Jordan Maufay, Marc Sciamanna, D Wolfersberger, and Nicolas Marsal

Doc ID: 379137 Received 30 Sep 2019; Accepted 07 Nov 2019; Posted 07 Nov 2019  View: PDF

Abstract: We study a pattern forming system driven by two counter propagating 2D Airy beams in a nonlinear single feedback configuration. When increasing the Airy beam power, modulation instability takes place but with several successive instability thresholds that correspond to destabilization of the different Airy beam satellite lobes. Most importantly, the self-organization is accompanied by a natural drifting dynamics related to the intrinsic acceleration of the Airy beam. The drifting dynamics is controlled by the Airy beam parameters. Numerical simulations reproduce the experimental findings.

Asymmetric near-zero edge mode in a topological photonic lattice

Kaiwen Ji, Zhengjuan Liu, Yanan Dai, Zengrun Wen, Yishan Wang, Guoquan Zhang, Jintao Bai, and Xinyuan Qi

Doc ID: 371790 Received 10 Jul 2019; Accepted 07 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: Generally speaking, a system will degenerate into a topological trivial one and the edge state will also disappear once the topological condition is violated, e.g., the values of the coupling constants in a waveguide array are exchanged. In this Letter, we study both theoretically and numerically the light dynamics in a photonic system without chiral or particle-hole symmetry. The results indicate that the system can restore its original Zak phase by removing an edge waveguide. Further study shows that the system can support an asymmetric near-zero mode on the right edge even if the Hamiltonian of the system is not chiral or particle-hole symmetric. Our work provides a new way to realize photonic near-zero mode which may have important applications in the future quantum computation.

Creation of complex nano-interferometric field structures

Zhongsheng Man, Peiwen Meng, and Shenggui Fu

Doc ID: 374530 Received 05 Aug 2019; Accepted 07 Nov 2019; Posted 08 Nov 2019  View: PDF

Abstract: With dual two-dimensional Airy-like waveforms, we demonstrate the creation of highly-confined electromagnetic fields in the transverse plane and circular or elliptical propagation trajectories in the longitudinal plane by using specially designed Pancharactnam–Berry (PB) phases. Applying the Richards and Wolf vectorial diffraction methods, the explicit expressions are obtained to calculate the strength vectors and energy flux of the three-dimensional electromagnetic fields. Calculations reveal that the nano-interferometric structures of such highly-confined fields highly depend on the indexes γ1 and γ2 determining the PB phase, thereby enabling the engineering of highly-confined fields with tunable size, spacing and propagation trajectories.

Spin-Hall effect of light and its enhancement in multi-level atomic system

Jinze Wu, junxiang zhang, Shi-Yao Zhu, and Girish Agarwal

Doc ID: 376559 Received 28 Aug 2019; Accepted 07 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: Using the sensitivity of atomic transitions on the polarizationsof pump fields in multi-Zeeman-sublevel atomic systems, we show the polarization-direction-dependent anisotropic susceptibility of atoms that yields the strong coupling between the spin and the transverse momentum of light, i.e., spin-orbit interaction (SOI). Moreover, we also show that the spin-Hall effect (SHE) of light can be obtained due to the SOI. It can be controlled via the orientation of the anisotropy and the frequency of light, and substantially enhanced up to several microns, which could be easily observed in experiment.

Bismuth plasmonics for extraordinary light absorption in deep sub-wavelength geometries

Imre Ozbay, Amir Ghobadi, Bayram Butun, and GONUL TURHAN-SAYAN

Doc ID: 379670 Received 15 Oct 2019; Accepted 06 Nov 2019; Posted 07 Nov 2019  View: PDF

Abstract: In this letter, we demonstrate an ultra-broadband metamaterial absorber of unrivaled bandwidth (BW) using extraordinary optical response of Bismuth (Bi) metal; a material selected through our analysis methodology. Based on our theoretical model, we investigate the maximum metal-insulator-metal (MIM) cavity BW achievable by any metal with a known n-k data. We show that an ideal metal in such structures should have positive real permittivity part in the near-infrared (NIR) regime. Contrary to noble and lossy metals utilized by most research groups within the field, this requirement is satisfied only by Bi, whose data greatly adheres to the ideal material properties predicted by our analysis. A Bi nano disc based MIM resonator with an absorption above 0.9 in an ultra-broadband range of 800 nm- 90 nm is designed, fabricated, and characterized. To the best of our knowledge, this is the broadest absorption BW reported for a MIM cavity in the near infrared with its upper to lower absorption edge ratio exceeding best contenders by more than 150%. According to the findings of this paper, the use of proper materials and dimensions will lead to realization of deep sub-wavelength efficient optical devices.

Amorphous Ga-Sb-Se thin films fabricated by co-sputtering

Tomáš Halenkovič, JAN GUTWIRTH, Marek Bouska, laurent calvez, Petr Nemec, and Virginie Nazabal

Doc ID: 378913 Received 02 Oct 2019; Accepted 05 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: Ternary chalcogenides of Ga-Sb-Se system are prospective materials for potential applications in the field of infrared optics. This letter deals with the optical properties and photosensitivity and of Ga-Sb-Se thin films deposited by co-sputtering, enabling to fabricate amorphous thin films outside the glass-forming region. The optical bandgap range 1.92-1.35 eV with corresponding refractive index at 1.55 μm ranging from 2.47-3.33 can be reliably covered using Ga2Se3 and Sb2Se3 targets. Furthermore, the prolonged irradiation by the near-bandgap light under the pure argon atmosphere leads to the irreversible photo-bleaching effect in fabricated films. The magnitude of this effect decreases monotonically with an increasing antimony content.

Q/V enhancement of micropillar resonator in BIC regime

Ivan Iorsh and Stanislav Kolodny

Doc ID: 380361 Received 31 Oct 2019; Accepted 05 Nov 2019; Posted 18 Nov 2019  View: PDF

Abstract: We show how the optical quasi-bound states in the continuum, recently predicted and observed in dielectric nanoantennae can be utilized to substantially enhance quality factor to mode volume ratio in pillar microcavities.

Cell-specific three-photon-fluorescence brain imaging: neurons, astrocytes, and gliovascular interfaces

Alexandr Lanin, Matvey Pochechuev, artem chebotarev, ilya kelmanson, Dmitry Bilan, Darya Kotova, Victor Tarabykin, Anatoly Ivanov, Andrey Fedotov, Vsevolod Belousov, and Aleksei Zheltikov

Doc ID: 377494 Received 11 Sep 2019; Accepted 04 Nov 2019; Posted 05 Nov 2019  View: PDF

Abstract: We present brain imaging experiments on rat cortical areas, demonstrating that, when combined with a suitable high-brightness, cell-specific genetically encoded fluorescent marker, three-photon-excited fluorescence (3PEF) enables subcellular-resolution, cell-specific 3D brain imaging modality that is fully compatible and readily integrable with other nonlinear-optical imaging modalities, including two-photon-fluorescence and harmonic-generation microscopy. With laser excitation provided by sub-100-fs, 1.25-μm laser pulses, cell-specific 3PEF from astrocytes and their processes detected in parallel with a three-photon-resonance-enhanced third harmonic from blood vessels is shown to enable a high-contrast 3D imaging of gliovascular interfaces.

Nanosecond pulsed 620 nm source by frequency-doubling a phosphosilicate Raman fiber amplifier

Anita Chandran, Timothy Runcorn, Robert T. Murray, and J. Taylor

DOI: 10.1364/OL.44.006025 Received 25 Oct 2019; Accepted 04 Nov 2019; Posted 12 Nov 2019  View: PDF

Abstract: We demonstrate a nanosecond pulsed source at 620 nm with watt-level average power by frequency-doubling a 1240 nm phosphosilicate Raman fiber amplifier. A gain-switched laser diode operating at 1064 nm is amplified in an ytterbium fiber master oscillator power amplifier system, and then converted to 1240 nm using a phosphosilicate Raman fiber amplifier with a conversion efficiency of up to 66%. The Raman fiber amplifier is seeded with a continuous-wave 1240 nm laser diode to obtain narrow-linewidth radiation, which is subsequently frequency-doubled in a periodically poled lithium tantalate crystal. A maximum average power of 1.5 W is generated at 620 nm, corresponding to a pulse energy of 300 nJ at a repetition rate of 5 MHz. The source has excellent beam quality (M² ≤ 1.16) and an optical efficiency (1064 nm to 620 nm) of 20%, demonstrating an effective architecture for generating red pulsed light for biomedical imaging applications.

Enhanced multiple-plane phase retrieval using adaptive support

Christian Ray Buco and Percival Almoro

DOI: 10.1364/OL.44.006045 Received 09 Sep 2019; Accepted 03 Nov 2019; Posted 04 Nov 2019  View: PDF

Abstract: In the single-plane phase retrieval method, the use of a fixed object support is not efficient and could lead to inaccurate reconstructions. While there have been adaptive support strategies for the single-plane method, numerical processing is slow because such strategies are based in the space domain. Here a novel adaptive support strategy based in the Fourier domain in conjunction with the multiple-plane phase retrieval method is presented and demonstrated through simulations and experiments. Optimisations of Fourier filter size and mask threshold parameters resulted in 3x faster convergence compared to the conventional multiple-plane method for the test object waves used. The proposed strategy offers fast and automated determination of the object support, affords the use of fewer intensity patterns, and can be adopted in other multiple intensity-based phase retrieval methods.

Intensity noise suppression of a high-power single-frequency CW laser by controlling the stimulated emission rate

Yongrui Guo, Huadong Lu, Weina Peng, Jing Su, and Kunchi Peng

DOI: 10.1364/OL.44.006033 Received 10 Oct 2019; Accepted 03 Nov 2019; Posted 06 Nov 2019  View: PDF

Abstract: The intensity noise of a high-power single-frequency continuous-wave laser is very harmful for applications in precise measurements and quantum communication. By simply lengthening the length of a laser resonator to decrease the stimulated emission rate of laser, the coupling strength of all noise sources into the resonant laser field will be reduced and thus the intensity noise of the output laser will be prominently suppressed. Based on theoretical analyses of the laser noise spectra, we experimentally implement a low noise high-power single-frequency laser with 1050 mm-long resonator. With the assistance of an intracavity imaging system and nonlinear second-harmonic-generation, the amplitude of resonant relaxation oscillation peak and the shot noise level (SNL) cutoff frequency are successfully reduced to 8.6 dB/Hz above the SNL and 1.0 MHz, respectively, under the output power of 16 W. The work provides an effective way to develop a high-quality laser with high output power and low intensity noise.

Carbon dioxide absorption spectroscopy with a mid-infrared silicon photonic waveguide

Floria Ottonello-Briano, Carlos Errando-Herranz, Henrik Rödjegård, Hans Martin, Hans Sohlström, and Kristinn Gylfason

Doc ID: 370397 Received 25 Jun 2019; Accepted 01 Nov 2019; Posted 06 Nov 2019  View: PDF

Abstract: Carbon dioxide is a vital gas for life on Earth, a waste product of human activities, and widely used in agriculture and industry. Its accurate sensing is therefore of great interest. Optical sensors exploiting the mid-infrared light absorption of CO₂ provide high selectivity, but their large size and high cost limit their use. Here, we demonstrate CO₂ gas sensing at 4.2 μm wavelength using an integrated silicon waveguide, featuring a sensitivity to CO₂ of 44 % that of free-space sensing. The suspended waveguide is fabricated on a silicon-on-insulator substrate by a single-lithography step process, and we route it into a mid-infrared photonic circuit for on-chip-referenced gas measurements. Its demonstrated performance and its simple and scalable fabrication make our waveguide ideal for integration in miniaturized CO₂ sensors for distributed environmental monitoring, personal safety, medical, and high-volume consumer applications.

Chirp-controlled high-harmonic and attosecond-pulse generation via coherent-wake plasma emission driven by mid-infrared laser pulses

Alexander Mitrofanov, Dmitry Sidorov-Biryukov, Pavel Borisovich, Mikhail Rozhko, Evgeny Stepanov, Anton Shutov, Sergey Ryabchuk, Aleksandr Voronin, Andrey Fedotov, and Aleksei Zheltikov

Doc ID: 374617 Received 05 Aug 2019; Accepted 29 Oct 2019; Posted 29 Oct 2019  View: PDF

Abstract: Coherent-wake plasma emission induced by ultrashort mid-infrared laser pulses on a solid target is shown to give rise to high-brightness, high-order harmonic radiation, offering a promising source of attosecond pulses and a probe for ultrafast subrelativistic plasma dynamics. With 80-fs, 0.2-TW pulses of 3.9-micrometer radiation used as a driver, optical harmonics up to the 34th order are detected, with their spectrum stretching from the mid-infrared to the extreme ultraviolet. The harmonic spectrum is found to be highly sensitive to the chirp of the driver. Particle-in-cell analysis of this effect suggests, in agreement with the generic scenario of coherent-wake emission, that optical harmonics are radiated as trains of extremely short, attosecond ultraviolet pulses with a pulse-to-pulse interval varying over the pulse train. A positive chirp of the driver pulse can partially compensate for this variation in the interpulse separation, allowing harmonics of highest orders to be generated in the plasma emission spectrum.

Angle-adjustment based tunable chirped mirrors with continuous dispersion compensation

Ruiyi Chen, yanzhi wang, Kesheng Guo, Yuhui Zhang, Zhihao Wang, Meiping Zhu, Kui Yi, Yuxin Leng, and Jianda Shao

Doc ID: 380701 Received 16 Oct 2019; Accepted 29 Oct 2019; Posted 04 Nov 2019  View: PDF

Abstract: We report the feasibility of continuously tunable dispersion control with chirped mirrors (CMs). The concept of tunable second-order and higher-order dispersion is also proposed. Our prototype dispersion-tunable CM makes it possible to provide continuous dispersion support, advancing CM technique to a new level by overcoming the drawback of discrete dispersion compensation nature of traditional CMs. This brings extremely convenience and flexibility to the compensation of the dispersion and ensures the tailored dispersion compensation in ultrafast laser systems. In our proof of concept study, continuously tunable group delay dispersion (GDD) is achieved by altering the angles of incidence (AOI) on the mirrors. Moreover, continuous duration tunable laser pulses are demonstrated by applying our GDD-tunable CMs in ultrafast laser system.

Broadband high quantum efficiency InGaAs/InP focal plane arrays via high precision plasma thinning

Wei He, Shao Xiumei, Yingjie Ma, Gaoqi Cao, Yu Chen, Xue Li, and Haimei Gong

DOI: 10.1364/OL.44.006037 Received 27 Aug 2019; Accepted 28 Oct 2019; Posted 06 Nov 2019  View: PDF

Abstract: We report on the fabrication of a 160×120 visible-extended (Vis-) InGaAs/InP focal plane array (FPA) by means of the inductive-coupled plasma etching. Compared to the conventional Vis-InGaAs FPAs, a higher quantum efficiency in visible spectrum has been achieved. High precision thinning of the n-type InP contact layer down to 10 nm has led to quantum efficiencies higher than 60% over a broad wavelength range of 500-1700 nm. Benefiting from the textured surface after the plasma etching, 17% lower reflectance over the entire response range was also found. Enhanced visible/near infrared laboratory imaging capability has also been demonstrated, which has proved the feasibility of such processes for fabrication of future higher definition VIS/NIR InGaAs imagers.

Tornado waves

Apostolos Brimis, Konstantinos Makris, and Dimitris Papazoglou

Doc ID: 374464 Received 01 Aug 2019; Accepted 28 Oct 2019; Posted 28 Oct 2019  View: PDF

Abstract: We show that light spiraling like a tornado can be generated by superimposing abruptly auto-focusing ring-Airy beams that carry orbital angular momentum of opposite handedness. The superimposing ring-Airy beams are tailored so that they abruptly auto-focus at overlapping focal regions although following distinct parabolic trajectories. This results to a complex wave with intense lobes that twist and shrink in an accelerating fashion along propagation. By achieving angular acceleration that exceeds 295 rad/mm², these Tornado waves can find broad application in laser trapping, direct laser writing and high harmonic generation.

Electric Field Vector Measurements Via Nanosecond Electric Field Induced Second Harmonic Generation

Tat Loon Chng, Maya Naphade, Benjamin Goldberg, Igor Adamovich, and Svetlana Starikovskaya

Doc ID: 374833 Received 15 Aug 2019; Accepted 19 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Electric field induced second harmonic generation, or E-FISH, has received renewed interest as a non-intrusive tool for probing electric fields in gas discharges and plasmas using ultrashort laser pulses. An important contribution of this work lies in establishing that the E-FISH method works effectively in the nanosecond regime, yielding field sensitivities of about a kV/cm at atmospheric pressure from a 16 ns pulse. This is expected to broaden its applicability within the plasma community, given the wider access to conventional nanosecond laser sources. A Pockels-cell-based pulse-slicing scheme, which may be readily integrated with such nanosecond laser systems, is shown to be a complementary and cost-effective option for improving the time resolution of the electric field measurement. Using this scheme, a time resolution of ~3 ns is achieved, without any detriment to the signal sensitivity. This could prove invaluable for non-equilibrium plasma applications, where time resolution of a few nanoseconds or less is often critical. Finally, we take advantage of the field vector sensitivity of the E-FISH signal to demonstrate simultaneous measurements of both the horizontal and vertical components of the electric field.

Reflection suppression via elastomeric films

David Miller, Marvin Alim, and Robert McLeod

DOI: 10.1364/OL.44.006021 Received 31 May 2019; Accepted 18 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: Transparent substrates introduce challenges in optical metrology, recording, and microscopy. Backside reflections reduce signal to noise, are recorded as artifacts, or introduce spurious signals. These reflections often need to be suppressed, but large angular and spectral bandwidths preclude the use of anti-reflection coatings. Using elastomeric materials doped with optical absorbers, we detail a method and a materials set for temporary suppression of Fresnel reflections for multiple substrates spanning wide spectral and angular bandwidth. Tuning the refractive index of the elastomer to match a substrate minimizes reflection, and the addition of different absorptive dopants allows for either broadband or wavelength-selective reflection suppression. As performance is limited only by index mismatch, both spectral and angular performance significantly exceed that of anti-reflection coatings. We demonstrate reflection suppression in excess of 30 dB spanning over 500 nm bandwidth. After use, these light traps may be removed and reused without damaging the substrate.

A Versatile and Scalable Fabrication Method for Laser Generated Focused Ultrasound Transducers

Esra Aytac Kipergil, Erwin Alles, Janvi Karia, Hendrik Pauw, Sacha Noimark, and Adrien Desjardins

Doc ID: 380611 Received 16 Oct 2019; Accepted 17 Oct 2019; Posted 25 Oct 2019  View: PDF

Abstract: A versatile and scalable fabrication method for laser-generated focused ultrasound transducers is proposed to address existing technical challenges for minimally invasive clinical applications. The method is based on stamping a coated negative mould onto polydimethylsiloxane (PDMS); it can be adapted to include different optical absorbers that are directly transferred or synthesized in situ. Transducers with a range of sizes down to 3 mm in diameter are presented, incorporating two carbonaceous (multiwalled carbon nanoparticles and candle soot nanoparticles) and one plasmonic (gold nanoparticles) optically absorbing components. The fabricated transducers operate at central frequencies in the vicinity of 10 MHz with bandwidths in the range of 15-20 MHz. A transducer with a diameter of 5 mm was found to generate a positive peak pressure greater than 35 MPa in the focal zone with a tight focal spot of 150 µm in lateral width. Ultrasound cavitation on the tip of an optical fibre was demonstrated in water for a transducer with a diameter as small as 3 mm. The transducers fabricated with carbonaceous components that have broad optical absorption spectra can accommodate many laser sources for ultrasound generation, whereas wavelength-selective absorbers are promising for multimodal applications.

Absorption of materials for achromatic lenses for multi-wavelength power lasers

Hervé PIOMBINI, Amira Guediche, and Gilles Damamme

Doc ID: 377348 Received 16 Sep 2019; Accepted 15 Oct 2019; Posted 22 Nov 2019  View: PDF

Abstract: When high power multi-wavelength lasers are used, the absorption AT in optical components can lead to distortion and depolarization of the laser beam or even damage on components. Photothermal deflection (P.D.) and interferometric calorimetry (I.C.) permit to quantify absorption of the laser flux in transparent materials by the measurement of the deflection or distortion of a probe beam caused by the propagation of a pump laser in the material. The purpose of this paper is to provide a method for measuring the absorption of a highly transparent material assisted by a thermal modeling.

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