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4×4 MIMO fiber-wireless transmission based on an integrated four-channel directly-modulated optical transceiver

Di Zhang, Yao Ye, Lei Deng, Li Di, Haiping Song, Yucheng Zhang, Minming Zhang, Shu Wang, and Deming Liu

Doc ID: 371612 Received 04 Jul 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: In this paper, an integrated compact four-channel directly modulated analog optical transceiver is proposed and fabricated. The 3-dB bandwidth of this optical transceiver exceeds 20 GHz, and the measured spurious-free dynamic range is up to 91.2 dB⋅Hz2/3. The optical coupling efficiency (CE) is improved by using a precise submicron alignment technique for lens coupling in transmitter optical sub-assembly, and the highest CE is achieved when the oblique angle of the AWG-PLC in receiver optical sub-assembly is set to 42°. Based on the proposed optical transceiver, we have experimentally demonstrated a 6.624 Gbit/s 4×4 multi-input multi-output (MIMO) 16QAM-OFDM radio signal over 15.5 km standard single mode fiber (SSMF), together with 1.2 m wireless transmission in both uplink and downlink. To cope with the channel interference and noise of the fiber-wireless transmission system, a low-complexity MIMO demodulation algorithm based on lattice reduction zero-forcing (LR-ZF) is designed. In our experiment, 1.8 dB power penalty is achieved by using the proposed LR-ZF algorithm, compared with the commonly used zero-forcing (ZF) algorithm. Moreover, this LR-ZF algorithm has much less complexity than the optimal maximum-likelihood sequence estimation (MLSE) at a given transmission performance. These results not only demonstrate the feasibility of the integrated optical transceiver for MIMO fiber-wireless application but also validate that the proposed LR-ZF algorithm is effective to eliminate the interference for hybrid fiber-wireless transmission.

Hybridization of Different Types of Exceptional Point

JINHYEOK RYU, Sunjae Gwak, Jaewon Kim, Hyeon-Hye Yu, ji-hwan kim, Ji-Won Lee, Chang-Hwan Yi, and Chil-Min Kim

Doc ID: 371951 Received 08 Jul 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: A large number of different types of second-order non-Hermitian degeneracies called exceptional points (EPs) were found in various physical systems depending on the mechanism of coupling between eigenstates. We show that these EPs can be hybridized to form higher-order EPs which preserve the original properties of the initial EPs before hybridization. For a demonstration, we hybridize a chiral and a supermode second-order EP, where the former and the latter are the results of an intra-disk and an inter-disk mode coupling in an optical system comprized of two Mie-scale microdisks and one Rayleigh-scale scatterer. High sensitivity of the resulting third order EP against external perturbations in our feasible system is emphasized.

The positive influence of the scattering medium on reflective ghost imaging

Yanfeng Bai, Qin Fu, Xianwei Huang, Suqin Nan, Peiyi Xie, and Xiquan Fu

Doc ID: 372802 Received 17 Jul 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: The scattering medium is usually thought to have a negative effect on imaging process. In this paper, it is shown that signal-to-noise ratio (SNR) of reflective ghost imaging (GI) in the scattering medium can be improved effectively when the binary method is used. By the experimental and the numerical results, it is proved that the existence of the scattering medium is just the cause of this phenomenon, i.e., the scattering medium has the positive effect on imaging quality of reflective GI. During this process, the effect from the scattering medium behaves as the random noise which makesimaging quality of binary ghost imaging (BGI) have an obvious improvement.

All-dielectric three-element transmissive Huygens’ metasurface performing anomalous refraction

Chang Liu, Lei Chen, Tiesheng Wu, Yumin Liu, Jing Li, Yu Wang, Zhongyuan Yu, Han Ye, and Li Yu

Doc ID: 376213 Received 23 Aug 2019; Accepted 13 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Metasurfaces have pioneered a new avenue for advanced wave-front engineering. Among various types of metasurfaces, Huygens’ metasurfaces are thought to be a novel paradigm for flat optical devices. Enabled by spectral overlapped electric resonance and magnetic resonance, Huygens’ metasurfaces are imparted with high transmission and full phase coverage of 2π, which makes them capable of realizing high-efficiency wave-front control. However, a defect of a Huygens’ metasurface is that its phase profile and transmissive response are both sensitive to the interaction of neighboring Huygens’ elements inside a metasurface unit. Consequently, the original assigned phase distribution can be distorted. In this work, we illustrate our design strategy of a transmissive Huygens’ metasurfaces performing anomalous refraction. We illustrate the investigation of Huygens’ elements realizing the overlapping between an electric dipole resonance and a magnetic dipole resonance based on the cross-shaped structures. We find that traditional discrete equidistant-phase design method is not enough to realize a transmissive Huygens’ surface due to the interaction between neighboring Huygens’ elements. Therefore, we introduce an extra optimization process on the spacing between the neighboring Huygens’ elements to palliate the phase distortion resulted from the interaction of Huygens elements. Based on this method, we successfully design an unequally-spaced three-element transmissive metasurfaces exhibiting an anomalous refraction effect. The anomalous refractive angle of the designed Huygens’ metasurface is 30°, which exceeds most of the anomalous refractive angles of present transmissive Huygens’ metasurfaces. A transmissive efficiency of 83.5% is numerically calculated at the operating wavelength. The far-field electric distribution shows that about 93% of transmissive light is directed along the 30-degree refractive direction. The deflection angle can be tuned by adjusting the number of Huygens elements in a metasurface unit cell. The design strategies used in this paper can be inspiring for other functional Huygens metasurface scheme.

Spatial and frequency multimode in dressing parametric amplified multi-wave mixing process

Xinghua Li, Ji Wu, Siqi Xiong, Mengting Chen, Hongye Yan, Zhiguo Wang, and Yanpeng Zhang

Doc ID: 368173 Received 22 May 2019; Accepted 11 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Quantum multimode of correlated fields are essential for future quantum correlated imaging. Here we investigate multimode properties in theoretically and experimentally for parametric amplified multi-wave mixing (PA-MWM) process. The multimode behavior of the signals in our system stems from spatial phase mismatching caused by frequency resonant linewidth δ. In the spatial domain, we observe the emission rings with an uneven distribution of photons intensity in parametric amplified four-wave mixing (PA-FWM) process, suggesting different spatial modes. The symmetrical distribution of spatial spots indicates the spatial correlation between the Stokes and anti-Stokes signals. While in the frequency domain, the multimode character is reflected as multiple peaks splitting in the signals’ spectrum. A novelty in our experiment, the number of multimode both in spatial and frequency domain can be controlled by dressing lasers via modifying the nonlinear susceptibility. Finally, we extend the multimode properties to multi-wave mixing process, the results can be applied in quantum imaging.

Experimental demonstration of full-field quantum optical coherence tomography

Roberto Ramirez Alarcón, Zeferino Ibarra, Carlos Sevilla Gutiérrez, HECTOR CRUZ-RAMIREZ, and Alfred U'Ren

Doc ID: 375318 Received 14 Aug 2019; Accepted 05 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: We present to the best of our knowledge the first implementation of full-field quantum optical coherence tomography (FF-QOCT). In our system, we are able to obtain full 3D information about the internal structure of a sample under study by relying on transversely-resolved Hong Ou Mandel (HOM) interferometry with the help of an intensified CCD (ICCD) camera. Our system requires a single axial scan, obtaining the full-field transverse single-photon intensity in coincidence with the detection of the sibling photon, for each value of the signal-idler temporal delay. We believe that this capability constitutes a significant step forward towards the implementation of QOCT as a practical biomedical imaging technique.

Cylindrical Vector Beam Fiber Laser with a Symmetric Two-Mode Fiber Coupler

Yang Xu, Su Chen, Zuxing Zhang, Bing Sun, hongdan wan, and Zhiqiang Wang

Doc ID: 371435 Received 08 Jul 2019; Accepted 05 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: We demonstrate a passively mode-locked all-fiber laser generating cylindrical vector beams (CVBs) just using a symmetric two-mode fiber optical coupler (TMF-OC) for both high-order mode excitation and splitting. Theoretical analyses show that for a symmetric TMF-OC with appropriate taper diameter, second-order mode can be excited and coupled into output tap with high purity, due to the effective index difference of different modes. Based on the fabricated TMF-OC, passively mode-locked fiber laser delivers pulsed CVBs at center wavelength of 1564.4 nm with 3-dB linewidth of 11.2 nm, pulse duration of 2.552 ps and repetition rate of 3.96 MHz. The purity of both radially and azimuthally polarized beams is estimated to be over 96%. Due to simple fabrication method of the TMF-OC and high purity of the generated CVBs, this mode-locked CVB fiber laser with all-fiber configuration has potential applications in optical trapping, optical communications, material processing, etc.

Microfluidic Integrated Metamaterials for Active Terahertz Photonics

Zhang Zhang, Ju Gao, Maosheng Yang, Xin Yan, Yuying Lu, Liang Wu, Jining Li, deiquan wei, Longhai Liu, Jianhua Xie, Lanju Liang, and Jian-Quan Yao

Doc ID: 374956 Received 08 Aug 2019; Accepted 02 Oct 2019; Posted 04 Oct 2019  View: PDF

Abstract: A depletion layer played by aqueous organic liquids flowing in a platform of microfluidic integrated metamaterials is experimentally used to actively modulate terahertz (THz) waves. The polar configuration of water molecules in depletion layer gives rise to a damping of THz waves. The parallel coupling of damping effect induced by depletion layer with the resonant response by metamaterials leads to an excellent modulation depth approaching 90 % in intensity and a great difference over 210 degrees in phase shift. Also, a tunability of slow light effect is displayed. Joint time-frequency analysis performed by the continuous wavelet transforms reveals the consumed energy with varying water content, indicating a smaller moment of inertia related with a shortened relaxation time of depletion layer. This work, as part of terahertz aqueous photonics, diametrically highlights the availability of water in THz devices, paving an alternative way of studying THz waves-liquid interactions and developing active terahertz photonics.

Azimuthal Vector Beam Exciting Silver Triangular Nanoprisms for Increasing Performance of Surface Enhanced Raman Spectroscopy

Lu Zhang, Wending Zhang, Fanfan Lu, Zhiqiang Yang, Tianyang Xue, min liu, Chao Meng, Peng Li, Dong Mao, Ting Mei, and Jianlin Zhao

Doc ID: 374624 Received 05 Aug 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Surface enhanced Raman spectroscopy (SERS) with high activity performance is a very necessary detection technology. Here, we present a method for increasing the performance of SERS based on the silver triangular nanoprisms arrays (ATNA) vertically excited via a focused azimuthal vector beam (AVB). The ATNA substrates with different structural parameters are prepared based on the self-assembled and modified film lifting off method. Based on a theoretical model established adopting the structural parameters of the ATNA substrates, theoretical calculation result shows that AVB excitation can achieve greater electric field enhancement than that of LPB excitation. Experimental result indicates that SERS activity obtained via AVB excitation is 10¯¹³ M by using the rhodamine 6G (R6G) as target analyte, which is two orders of magnitude lower than that of LPB excitation (10¯¹¹ M). Meanwhile, the uniformity and reproducibility of the ATNA substrates are respectively examined by using Raman mapping and batch-to-batch measurement, and the Raman enhancement factor is calculated to be ~3.3×10⁷. This method of vector light field excitation may be used to improve the SERS performance of the substrates in fields of ultra-activity Raman detection.

Frequency-multiplexing photon-counting multi-beam LiDAR

Guang Wu, Tianxiang Zheng, Guangyue Shen, Zhaohui Li, Lei Yang, HaiYan Zhang, and E Wu

Doc ID: 374729 Received 06 Aug 2019; Accepted 29 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: We report a frequency-multiplexing method for multi-beam photon-counting LiDAR, where only one single-pixel single-photon detector is employed to simultaneously detect the multi-beam echoes. In this frequency multiplexing multi-beam LiDAR, each beam is from an independent laser source with different repetition rate and independent phase. As a result, the photon counts from different beams could be discriminated from each other due to the strong correlation between the laser pulses and their respective echo photons. A 16-beam LiDAR was demonstrated in three-dimensional laser imaging with 16 pulsed laser diodes at 850 nm and one Si avalanche photodiode single-photon detector. This frequency-multiplexing method can greatly reduce the number of single-photon detectors in multi-beam lidar systems, which may be useful for eye-safety and low-cost LiDAR applications.

One-to-many optical information encryption transmission method based on temporal ghost imaging and code division multiple access

Kang Yi, leihong zhang, ye hualong, mantong zhao, Saima Kanwal, Bai Chunyan, and Dawei Zhang

Doc ID: 371325 Received 01 Jul 2019; Accepted 23 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: A method is presented for one-to-many information encryption transmission by using the temporal ghost imaging and code division multiple access. In the encryption transmission process, code division multiple access technologies combine multiple information and the chip sequence corresponding to each information is used as the first key. The transmission end loads the transmission information onto a series of temporal random patterns of temporal ghost imaging and transmits it to the receivers. A series of temporal random patterns is the second key. During the decryption, each receiver can get the same encrypted information and use the second key to obtain the transmitted information. Finally, each receiver uses the unique chip sequence to get corresponding information. This encryption transmission method realizes one-to-many information encryption transmission at the same time over the same channel. Double Encryption ensures the security of information. Simulation and experiment results verify the effectiveness and security of the method. The method has strong anti-noise ability and can effectively resist various attack modes. At the same time, this method solves the problem that the use of code division multiple access enlarges the signal bandwidth, and ensures that no crosstalk occurs between various information.

Low power (mW) nonlinearities of polarization maintaining fibers

Hanieh Afkhamiardakani, Luke Horstman, Ladan Arissian, and Jean-Claude Diels

Doc ID: 372988 Received 17 Jul 2019; Accepted 23 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Polarization maintaining (PM) fibers are meant to maintain linear polarization along a preferred axis. A PM fiber can be seen as the fiber version of a very high order waveplate, designed with different refractive indices along two orthogonal axes. It is shown that monitoring the polarization of initially circularly polarized light sent through a PM fiber, leads not only to new sensing methods, but also to power control, saturable absorption, and optical path stabilization. Even at peak power levels not exceeding a few mW, nonlinear transmission is detected, with time constants in the microsecond range.

Optimization of temporal gate by the two-color chirped lasers for the generation of isolated attosecond pulse in the soft X-rays

Cheng Jin, Liwei He, Guanglu Yuan, Kan Wang, Weijie Hua, and Chao Yu

Doc ID: 372966 Received 17 Jul 2019; Accepted 22 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: We propose a simple and efficient method to optimize the two-color chirped laser pulses to form a “temporal gate" for the generation of isolated attosecond pulse (IAP) in the soft X-rays. We show that the generation process for higher and cutoff harmonics can be effectively limited within the “temporal gate", and the harmonic emission interval can be further reduced with the help of phase-matching by only selecting the contribution from short-trajectory electrons. This two-color gating mechanism is verified byincreasing the pulse duration, raising gas pressure, and extending the target cutoff. Compared to the five-color waveform in [Phys. Rev. Lett. 102, 063003 (2009)], our waveform can be used to generate the IAP in the long-duration laser pulse while the cutoff energy is higher without the reduction of harmonic yields. Our work provides with an alternative temporal gating scheme for the generation of IAPs by simultaneously improving the harmonic conversion efficiency, thus helping the attosecond soft X-rays to be an intense and highly time-resolved table-top light source for future applications.

Direct Observation of Interlayer Coherent Acoustic Phonon Dynamics in Bilayer and Few-Layer PtSe₂

Xin Chen, Saifeng Zhang, Lei Wang, Yi-Fan Huang, Huiyan Liu, Wei Huang, Ningning Dong, Weimin Liu, Ivan Kislyakov, Jean-Michel Nunzi, Long Zhang, and Jun Wang

Doc ID: 378236 Received 19 Sep 2019; Accepted 20 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: This work reports the real-time observation of the interlayer lattice vibrations in bilayer and few-layer PtSe₂ by means of coherent phonon method. The layer-breathing mode and standing wave mode of the interlayer vibrations are found to coexist in such kind of group-10 transition metal dichalcogenides (TMDCs). The interlayer breathing force constant standing for perpendicular coupling (per effective atom) is derived as 7.5 N/m, 2.5 times larger than that of graphene. The interlayer shearing force constant is comparable to the interlayer breathing force constant, which indicates that PtSe₂ has nearly isotropic interlayer coupling. The low-frequency Raman spectroscopy elucidates the polarization behavior of the layer breathing mode that is assigned to have A1g symmetry. The standing wave mode shows red-shift with the increasing number of layers, which successfully determines the out-of-plane sound velocity of PtSe₂ experimentally. Our results manifest that coherent phonon method is a good tool to uncover the interlayer lattice vibrations, beyond the conventional Raman spectroscopy limit. The strong interlayer interaction in group-10 TMDCs reveals their promising potential in high-frequency (~THz) micro-mechanical resonators.

A physical picture of the optical memory effect

Honglin Liu, Zhentao Liu, Meijun Chen, Shensheng Han, and Lihong Wang

Doc ID: 370998 Received 26 Jun 2019; Accepted 19 Sep 2019; Posted 20 Sep 2019  View: PDF

Abstract: The optical memory effect is an interesting phenomenon attracting a considerable amount of attentions in decades. Here, we present a new physical picture of the optical memory effect, in which the memory effect and the conventional shift invariance are united. Based on this picture we depict the role of thickness, scattering times and anisotropy factor and derive equations to calculate the ranges of the angular memory effect (AME) of different scattering components (ballistic light, singly scattered, doubly scattered, etc.), hence a more accurate equation for the real AME ranges of volumetric turbid media. A conventional random phase mask model is modified according to the new picture. The self-consistency of the simulation model and its agreement with experiment demonstrate the rationality of the model and the physical picture, which provide powerful tools for more sophisticated studies of the memory effect related phenomena and wavefront sensitive techniques, such as wavefront shaping, optical phase conjugation and optical trapping in/through scattering media.

Integrated flat-top reflection filters operating near bound states in the continuum

Leonid Doskolovich, Evgeni Bezus, and Dmitry Bykov

Doc ID: 372279 Received 10 Jul 2019; Accepted 12 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: We propose and theoretically and numerically investigate narrowband integrated filters consisting of identical resonant dielectric ridges on the surface of a single-mode dielectric slab waveguide. The proposed composite structures operate near a bound state in the continuum (BIC) and enable spectral filtering of transverse-electric-polarized guided modes propagating in the waveguide. We demonstrate that by proper choice of the distances between the ridges, flat-top reflectance profiles with steep slopes and virtually no sidelobes can be obtained using just a few ridges. In particular, the structure consisting of two ridges can optically implement the second-order Butterworth filter, whereas at a larger number of ridges, excellent approximations to higher-order Butterworth filters can be achieved. Owing to the BIC supported by the ridges constituting the composite structure, the flat-top reflection band can be made arbitrarily narrow without increasing the structure size. In addition to the filtering properties, the investigated structures support another type of BICs — Fabry–Pérot BICs arising when the distances between the adjacent ridges meet the Fabry–Pérot resonance condition. In the vicinity of the Fabry–Pérot BICs, an effect similar to the electromagnetically induced transparency is observed, namely, sharp transmittance peaks against the background of a wide transmittance dip.

Polarization evolution dynamics of dissipative soliton fiber laser

Lei Gao, Yu Long Cao, Stefan Wabnitz, Hongqing Ran, Lingdi Kong, Yujia Li, Wei Huang, Ligang Huang, Danqi Feng, and Tao Zhu

Doc ID: 373626 Received 24 Jul 2019; Accepted 12 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: Dissipative solitons emerge as stable pulse solutions of non-integrable and non-conservative nonlinear physical systems, owing to a balance of nonlinearity, dispersion, and loss/gain. A considerable research effort has been dedicated to characterize amplitude and phase evolutions in the spatio-temporal dynamics of dissipative solitons emerging from fiber lasers. Yet, the picture of the buildup process of dissipative solitons in fiber lasers is incomplete, in the absence of corresponding information about the polarization evolution. Here, we characterize probabilistic polarization distributions in the buildup of dissipative solitons in a net-normal dispersion fiber laser system, mode-locked by single-wall carbon nanotubes. The output optical spectra under different pump powers are filtered by a tunable filter, and are detected by a polarization state analyzer. The laser system operates from random amplified spontaneous emission into a stable dissipative soliton state as the cavity gain is progressively increased. Correspondingly, the state of polarization of each spectral wavelength converges towards a fixed point. To reveal the invariant polarization relationship among the various wavelength components of the laser output field, the phase diagram of the ellipticity angle and the spherical orientation angle are introduced. We find that, within the central spectral region of the dissipative soliton, the state of polarization evolves with frequency by tracing a uniform arc on the Poincaré sphere. Whereas in the edges of the dissipative soliton spectrum the state of polarization abruptly changes its path. Increasing cavity gain leads to spectral broadening, accompanied by a random scattering of the state of polarization of newly generated frequencies. Further increases of pump power result into dissipative soliton explosions, accompanied by the emergence of a new type of optical polarization rogue waves. These experimental results provide a deeper insight into the transient dynamics of dissipative soliton fiber lasers.

Optimized weak measurement of orbital angular momentum-induced beam shifts in optical reflection

Wenguo Zhu, Jintao Pan, Xinyi Guo, Xiaohe Liu, Haolin Lin, Huadan Zheng, JianHui Yu, Heyuan Guan, Huihui Lu, Yongchun Zhong, Shenhe Fu, wenjin long, Li Zhang, and Zhe Chen

Doc ID: 367234 Received 10 May 2019; Accepted 11 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: Tiny but unavoidable beam shifts occur when a polarized light beam reflected upon a planar interface. Although the beam shifts of Gaussian beams have been well measured by weak measurement technique, the weak measurement for orbital angular momentum (OAM)-induced spatial shifts of vortex beams are still missing. Here, by elaborative choosing the preselection and postselection states, the tiny OAM-induced shifts are amplified at an air-prism interface. The maximum shifts along directions both parallel and perpendicular to the incident plane are theoretically predicted and experimentally verified with optimal preselection and postselection states. These maximum shifts can be used to determine OAM of vortex beams.

Pattern formation in 2-μm Tm Mamyshev oscillators associated with the dissipative Faraday instability

Changxi Yang, Pan Wang, Shunyu Yao, Philippe Grelu, and Xiaosheng Xiao

Doc ID: 369503 Received 06 Jun 2019; Accepted 11 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: We investigate numerically pattern formation in 2-μm thulium-doped Mamyshev fiber oscillators, associated with the dissipative Faraday instability. The dispersion-managed fiber ring oscillator is designed with commercial fibers, allowing to study the dynamics for a wide range of average dispersion regimes, from normal to near-zero cavity dispersion where the Benjamin-Feir instability remains inhibited. For the first time in the 2-μm spectral window, the formation of highly coherent periodic patterns is demonstrated numerically with rates up to ∼100 GHz. In addition, irregular patterns are also investigated, revealing the generation of rogue waves (RWs) via nonlinear collision processes. Our investigations have potential applications for the generation of multi-GHz frequency combs. They also shed new light on the dissipative Faraday instability mechanisms in the area of nonlinear optical cavity dynamics.

Mode- and Wavelength-Multiplexed Transmission withCrosstalk Mitigation Using a Single Amplified Spontaneous Emission (ASE) Source (Invited)

Yetian Huang, Haoshuo Chen, Hanzi Huang, Zhengxuan Li, Nicolas Fontaine, Roland Ryf, Juan Carlos Alvarado Zacarias, Rodrigo Amezcua Correa, John van Weerdenburg, Chigo Okonkwo, Ton Koonen, Yingxiong Song, and Min Wang

Doc ID: 370890 Received 24 Jun 2019; Accepted 10 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: We propose to use the low-coherence property of the amplified spontaneous emission (ASE) noise to mitigate optical crosstalk such as spatial, polarization and modal crosstalk, which currently limits the density of photonic integration and fibers for dense space division multiplexing (SDM). High optical crosstalk tolerance can be achieved by ASE-based low-coherence matched detection, which avoids dedicated optical lasers and uses spectrally filtered ASE noise as the signal carrier and as a matched local oscillator. We experimentally demonstrate spatial and modal crosstalk reduction in multimode fiber (MMF) and realize mode- and wavelength-multiplexed transmission over 1.5-km multimode fiber (MMF) supporting three spatial modes using a single ASE source. Performance degradation due to model dispersion over MMF is experimentally investigated.

High-Speed Optical Secure Communication with External Noise Source and Internal Time-Delayed Feedback Loop

Yudi Fu, Mengfan Cheng, xingxing jiang, Quan Yu, Linbojie Huang, Lei Deng, and Deming Liu

Doc ID: 371592 Received 03 Jul 2019; Accepted 10 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: We proposed and experimentally demonstrated a novel physical layer encryption scheme for high-speed optical communication. 10 Gb/s on-off keying (OOK) signal is secretly transmitted over 100 km standard single mode fiber (SSMF). The intensity-modulated message is secured by the encryption mechanism, which is composed of an external noise source and an internal time-delayed feedback loop. The external noise serves as an entropy source with sufficient randomness. The feedback loop structure in the transmitter introduces a time-domain encryption key space, and a corresponding open-loop configuration at the receiver side is used for synchronization and decryption. Experiment results show the effectiveness of the proposed scheme. For a legitimate terminal, bit error rate below 10^-8 can be obtained. Decryption degradations with the mismatch of different hardware parameters are researched. The time-delay in the feedback loop provides a sensitive encryption key. For other hardware parameters, the system is robust enough for synchronization. Meanwhile, the time-delay signature of the loop is able to be well-concealed by the external noise. Moreover, the proposed scheme can support density wavelength division multiplexing (DWDM) transmission with a relatively simple structure. This work also provides a new concept to establish optical secure communication by combining time-delayed feedback chaotic system and random noise.

Dual waveband generator of perfect vector beams

Hui Li, Haigang Liu, and Xianfeng Chen

Doc ID: 373629 Received 25 Jul 2019; Accepted 10 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: Recently, perfect vector (PV) beam sparks considerable interest because of its radius is independent of the topological charge, which has demonstrated the special capabilities in optical manipulation, microscopy imaging, and laser micromachining. Previous researches about the generation and manipulation of such PV beams only focus on the linear optical fields. Therefore, the generation of nonlinear PV beams is still lacking. Here, we propose a dual waveband generator to simultaneously generate the PV beams in linear and nonlinear wavebands. In our experiment, PV beams with different polarization states are realized. It is proved that the polarization states of the generated PV beams can be flexibly adjusted by changing the axis direction of a half wave plate. The experimental results show that the radiuses of the generated PV beams are equal and independent of the topological charges. With proper alteration of the nonlinear crystals, this approach could be further extended to other nonlinear processes, such as sum-frequency and difference frequency generation.

Design, fabrication and characterization of highly nonlinear few-mode fiber

Jitao Gao, Elham Nazemosadat, CHEN YANG, Songnian Fu, Ming Tang, Weijun Tong, Joel Carpenter, Jochen Schröeder, Magnus Karlsson, and Peter Andrekson

Doc ID: 370042 Received 20 Jun 2019; Accepted 09 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: We present the design, fabrication and characterization of a highly-nonlinear few-mode fiber (HNL-FMF) with an inter-modal nonlinear coefficient of 2.84 (W · km)^(-1), which to the best of our knowledge is the highest reported to date. The graded-index circular core fiber supports two mode groups (MGs) with 6 eigenmodes and is highly doped with germanium. This breaks the mode degeneracy within the higher-order MG, leading to different group velocities among corresponding eigenmodes. Thus, the HNL-FMF can support multiple inter-modal four-wave mixing processes between the two MGs, at the same time. In a proof of concept experiment, we demonstrate simultaneous inter-modal wavelength conversions among three eigenmodes of the HNL-FMF over the C-band.

Coherence of bulk-generated supercontinuum

Atri Halder, Vytautas Jukna, Matias Koivurova, Audrius Dubietis, and Jari Turunen

Doc ID: 369321 Received 05 Jun 2019; Accepted 08 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: We have developed a numerical framework, that allows to estimate of coherence in spatio-temporal and spatio-spectral domains. Correlation properties of supercontinuum (SC) pulses generated in bulk medium are investigated by means of second-order coherence theory of non-stationary fields. The analysis is based on simulations of individual space-time and space-frequency realizations of pulses emerging from a 5~mm thick sapphire plate, in the regimes of normal, zero and anomalous group velocity dispersion. The temporal and spectral coherence properties are analyzed in the near (as a function of spatial position at the exit plane of the nonlinear medium) and as a function of propagation direction (spatial frequency) in the far field. Unlike in fiber-generated SC, the bulk case features spectacularly high degrees of temporal and spectral coherence in both the spatial and spatial-frequency domains, with increasing degrees of coherence at higher pump energies. When operating near the SC generation threshold, the overall degrees of temporal and spectral coherence exhibit an axial dip in the spatial domain, whereas in the far field it is the highest around the optical axis.

Experimental test of error-disturbance uncertainty relation with continuous variables

Xiaolong Su, Yang Liu, Haijun Kang, Dongmei Han, and Kunchi Peng

Doc ID: 363791 Received 03 Apr 2019; Accepted 07 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: Uncertainty relation is one of the fundamental principle in quantum mechanics and plays an important role in quantum information science. We experimentally test the error-disturbance uncertainty relation (EDR) with continuous variables for Gaussian states. Two conjugate continuous-variable observables, amplitude and phase quadratures of an optical mode, are measured simultaneously by using a heterodyne measurement system. The EDR with continuous variables for a coherent state, a squeezed state and a thermal state are verified experimentally. Our experimental results demonstrate that Heisenberg's EDR with continuous variables is violated, yet Ozawa's and Branciard's EDR with continuous variables are validated.

Interference-enhanced magnetism in surface Mie resonators: a pathway towards high-performance ultracompact linear and nonlinear meta-optics

Lei Kang, Huaguang Bao, and Douglas Werner

Doc ID: 371256 Received 28 Jun 2019; Accepted 06 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: Artificial magnetism at optical frequencies is one of the most intriguing phenomena associated with metamaterials. Magnetic Mie resonance of high index resonators provides an alternative approach to achieving optical magnetism with simple structures. Given the generally moderate refractive index exhibited by available materials at optical frequencies, Mie resonances usually suffer from coupling between the multipole modes and the corresponding response of the Mie metasurfaces can be analyzed based on the concept of “meta-optics”. Here we show that the optical magnetism in Mie resonators can be significantly enhanced by adding a highly reflective back mirror to the system. To highlight the transformative ability of this approach for improving meta-optics in the linear and nonlinear regimes, two proof-of-concept demonstrations are presented. Theoretical modeling reveals that low-pump power ultrafast nonlinear optics can be realized in periodic Si nanodisk arrays backed with a gold film, a system supporting guided resonance modes. Moreover, based on the enhanced magnetism of individual Mie resonators, a pair of the silicon cuboids is demonstrated as a magnetic antenna for directional excitation of surface plasmon waves. The interference-enhanced magnetism of Mie resonators provides a disruptive technology for enabling meta-optics comprising ultracompact, high-speed and power-efficient photonic devices.

Third-order nonlinear optical properties of WTe2 films synthesized by pulsed laser deposition

Zhaoyu Ren, Mi He, Yequan Chen, Lipeng Zhu, Huan Wang, Xuefeng Wang, and Xinlong Xu

Doc ID: 369330 Received 04 Jun 2019; Accepted 06 Sep 2019; Posted 06 Sep 2019  View: PDF

Abstract: The prominent third-order nonlinear optical properties of WTe2 films were studied through the Z-scan technique equipped with a femtosecond pulsed laser at 1030 nm. Open-aperture (OA) Z-scan measurements under different intensities show that WTe2 films always hold a saturable absorption characteristic without transition to reverse saturable absorption. The nonlinear absorption coefficient β is -3.37 cm/GW by fitting the Z-scan curve at the peak intensity of 15.603 GW/cm2. The excited state absorption cross section and absorber's density were found to be respectively 6.9×10−19 cm3 and 2.8×1018 cm−3. Closed-aperture (CA) Z-scan measurements exhibit a classic peak-valley shape of CA Z-scan signal, which reveals a self-defocusing optical effect of WTe2 films under measured environment. The magnitude and sign of third-order nonlinear refractive index n2 of WTe2 can be obtained to be -4.022×10-2 cm2/GW. Furthermore, the values of real and imaginary parts of the third-order nonlinear susceptibility of WTe2 are roughly estimated to be -5.93×10-9 esu and -1.01×1-8 esu with the help of first-principles calculations. The third-order nonlinear optical response of WTe2 films suggests the potential applications in nonlinear optical devices.

Overcoming the barrier of nanoparticle production by femtosecond laser ablation in liquids using simultaneous spatial and temporal focusing

Carlos Doñate Buendía, Mercedes Fernández Alonso, Jesus Lancis, and Gladis Vega

Doc ID: 364554 Received 08 Apr 2019; Accepted 04 Sep 2019; Posted 06 Sep 2019  View: PDF

Abstract: There exist an increasing demand of industrial scale production of high purity ligand free nanoparticles due to the continuous development of biomedical, catalysis and energy applications. In this contribution, a simultaneous spatial and temporal focusing (SSTF) setup is firstly proposed for increasing nanoparticle productivity of the eco-friendly pulsed laser ablation in liquids (PLAL) technique. In spite of the fact that femtosecond pulses have proved to achieve higher ablation rates in air than picosecond pulses, in PLAL this is reversed due to the nonlinear energy losses in the liquid. However, thanks to the incorporation of SSTF, the energy delivered to the target is increased up to a 70%, which leads to a nanoparticle production increase of a 2.4 factor. This breaks a barrier towards the employment of femtosecond lasers in high efficiency PLAL.

Frequency-modulated textural formation and optical properties of a binary rod-like/bent-core cholesteric liquid crystal

Wei Lee, Yueh-Chern Lin, and Po-Chang Wu

Doc ID: 372034 Received 08 Jul 2019; Accepted 03 Sep 2019; Posted 06 Sep 2019  View: PDF

Abstract: We explore the mechanisms of voltage-induced textural switching and the corresponding electro-optical responses of a binary cholesteric liquid crystal (CLC) composed of the rod-like nematic LC E7 with positive dielectric anisotropy and the bent-core LC dimer CB7CB with large flexoelectric coefficients. Our results indicate that the minimal voltage (VH) required for retaining the CLC in the homeotropic state and the voltage-induced formations of the CLC stable configurations, such as the focal conic (FC), the uniform lying helix (ULH), and the ULH/FC mixed states, together with their optical transmittance are dependent of the voltage frequency, characterized by the frequency regimes separated by the critical frequencies of flexoelectric polarization and dielectric relaxation in dielectric dispersion. These unusual features, which cannot be demonstrated in conventional rod-like CLCs, are explained by the dielectric and frequency-dependent flexoelectric responses of LC molecules to an external AC voltage. Accordingly, in addition to the known Grandjean planar and FC states, the ULH as a third stable state can be feasibly generated in the binary CLC with 45-wt% CB7CB by treating the cell directly with a sufficient voltage lower than VH or by decreasing the voltage gradually from VH to zero in the low-frequency regime, where the strength of flexoelectric coupling with the electric field is significant. Manifested by its optical tristability, frequency-controllable optical transparency and fast flexoelectro-optical response, the proposed binary rod-like/bent-core CLC system is promising for developing a variety of memory- and dynamic-mode photonic and optoelectronic devices.

Bosonic discrete supersymmetry for quasi-two-dimensional optical arrays

QI ZHONG, Seth Nelson, Mercedeh Khajavikhan, Demetrios Christodoulides, and Ramy El-Ganainy

Doc ID: 363826 Received 01 Apr 2019; Accepted 03 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: We apply the notion of discrete supersymmetry based on matrix factorization to quantum systems consisting of coupled bosonic oscillators, to construct isospectral bosonic quantum networks. By using the algebra that arises due to the indistinguishability of bosonic particles, we then write down the Schrödinger equations for these oscillators in the different boson-number sectors. By doing so, we obtain, for every partner quantum network, a system of coupled differential equations that can be emulated by classical light propagation in optical waveguide arrays. This mathematical scheme allows us to build quasi-two-dimensional optical arrays that are either isospectral or share only a subset of their spectrum after deliberately omitting some chosen eigenstates from the spectrum. As an example, we use this technique (which we call bosonic discrete supersymmetry or BD-SUSY) to design two optical, silica-based waveguide arrays consisting of six and three elements, respectively with overlapping eigenspectrum.

Light rays and waves on geodesic lenses

Huanyang Chen, Lin Xu, Xiangyang Wang, Chong Sheng, Shining Zhu, Hui Liu, and Tomas Tyc

Doc ID: 365526 Received 18 Apr 2019; Accepted 03 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: Starting from well-known absolute instruments that provide perfect imaging, we analyze a class of rotationally-symmetric compact closed manifolds, namely geodesic lenses. We demonstrate that light rays confined on geodesic lenses form closed trajectories, and that for optical waves, the spectrum of geodesic lens is (at least approximately) degenerate and equidistant. Moreover, we fabricate two geodesic lenses in micrometer and millimeter scale and observe curved light rays along closed geodesics. Our experimental setup may offer a new platform to investigate light propagation on curved surfaces.

Generation of optical Fock and W states with single-atom based bright quantum scissors

Barak Dayan, Ziv Aqua, and Myungshik Kim

Doc ID: 363933 Received 03 Apr 2019; Accepted 01 Sep 2019; Posted 04 Sep 2019  View: PDF

Abstract: We introduce a multi-step protocol for optical quantum state engineering that performs as deterministic "bright quantum scissors" (BQS), namely truncates an arbitrary input quantum state to have at least a certain number of photons. The protocol exploits single-photon pulses and is based on the effect of single-photon Raman interaction, which is implemented with a single three-level Λ system (e.g. a single atom) Purcell-enhanced by a single-sided cavity. A single step of the protocol realises the inverse of the bosonic annihilation operator. Multiple iterations of the protocol can be used to deterministically generate a chain single-photons in a W state. Alternatively, upon appropriate heralding, the protocol can be used to generate Fock-state optical pulses. This protocol could serve as a useful and versatile building block for the generation of advanced optical quantum states that are vital for quantum communication, distributed quantum information processing, and all-optical quantum computing.

Engineering of strong mechanical squeezing via the joint effect between Duffing nonlinearity and parametric pump driving

Cheng-Hua Bai, Dong-Yang Wang, Shou Zhang, Shutian Liu, and Hong-Fu Wang

Doc ID: 366935 Received 07 May 2019; Accepted 01 Sep 2019; Posted 04 Sep 2019  View: PDF

Abstract: Previous works for achieving mechanical squeezing focused mainly on the sole squeezing manipulation method. Here we study how to construct strong steady-state mechanical squeezing via the joint effect between Duffing nonlinearity and parametric pump driving. We find that the 3 dB limit of strong mechanical squeezing can be easily overcome from the joint effect of two different below 3 dB squeezing components induced by Duffing nonlinearity and parametric pump driving, respectively, without the need of any extra technologies, such as quantum measurement or quantum feedback. Specially, we first demonstrate that, in the ideal mechanical bath, the joint squeezing effect just is the superposition of the two respective independent squeezing components. The mechanical squeezing constructed by the joint effect is fairly robust against the mechanical thermal noise. Moreover, different from previous mechanical squeezing detection schemes, which need to introduce an additional ancillary cavity mode, the joint mechanical squeezing effect in the present scheme can be directly measured by homodyning the output field of the cavity with an appropriate phase. The joint idea opens up a new approach to construct strong mechanical squeezing and can be generalized to realize other strong macroscopic quantum effects.

Ultra-flat dispersion in an integrated waveguide with five and six zero-dispersion wavelengths for mid-infrared photonics

Yuhao Guo, Zeinab Jafari, Lijuan Xu, Changjing Bao, Peicheng Liao, Guifang Li, Anuradha Agarwal, Lionel Kimerling, Jurgen Michel, Alan Willner, and Lin Zhang

Doc ID: 368319 Received 24 May 2019; Accepted 30 Aug 2019; Posted 30 Aug 2019  View: PDF

Abstract: We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion (GVD) profile with 5 and 6 zero-dispersion wavelengths (ZDWs). The dispersion value varies from -0.15 to 0.35 ps/nm/km from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than one order of magnitude. We explain the principle of producing 6 ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.

Investigating the properties of UV-emitting nitride semiconductor thin films in the scanning electron microscope

Carol Trager-Cowan, Aeshah ALASAMARI, William Avis, Jochen Bruckbauer, Paul Edwards, Benjamin Hourahine, Simon Kraeusel, Gunnar Kusch, Ross Johnston, G. Naresh-Kumar, Robert Martin, M. Nouf-Allehiani, Elena Pascal, Lucia Spasevski, David Thomson, Stefano Vespucci, Peter Parbrook, Matt Smith, Johannes Enslin, Frank Mehnke, M Kneissl, Christian Kuhn, Tim Wernicke, Arne Knauer, Viola Kueller, Sylvia Hagedorn, Sebastian Walde, Markus Weyers, Pierre-Marie Coulon, Philp Shields, Yun Zhang, Ling Jiu, Yipin Gong, T Wang, Aimo Winkelmann, and Richard Smith

Doc ID: 361722 Received 06 Mar 2019; Accepted 28 Aug 2019; Posted 11 Sep 2019  View: PDF

Abstract: In this article we provide an overview of the scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI), wavelength dispersive X-ray spectroscopy (WDX) and cathodoluminescence (CL) hyperspectral imaging. We describe the application of these non-destructive techniques to provide complementary information on the topography, crystal misorientation, defect distributions, composition, doping and light emission from ultraviolet (UV) emitting nitride semiconductor thin films, namely GaN, AlGaN and AlN.

14 μm quantum cascade lasers based on nonresonant four-level system

Shouuzhu Niu, Junqi Liu, fengmin cheng, huan wang, jinchuan zhang, Ning Zhuo, Shenqiang Zhai, lijun wang, Shuman Liu, Liu Fengqi, Zhanguo Wang, Xiaohua Wang, and Zhipeng Wei

Doc ID: 367589 Received 14 May 2019; Accepted 27 Aug 2019; Posted 30 Aug 2019  View: PDF

Abstract: We report InP-based room temperature high average power quantum cascade lasers emitting at 14 μm. Using a nonresonant four-level system active region design, a bound-to-bound lasing transition is guaranteed by efficient electron injection into the upper laser level and fast electron extraction through miniband from the lower laser level. For a 4 mm long and 40 μm wide double channel ridge waveguide laser with 55 stages of active region, the threshold current density is only 3.13 kA/cm2 at room temperature. At 293 K, the maximum single facet peak power and average power is up to 830 mW and 75 mW, respectively. The laser exhibits a characteristic temperature T0 of 395 K over a temperature range from 293 K to 353 K.

Dynamic and nonlinear properties of epitaxial quantum dot lasers on silicon for isolator-free integration

Jianan Duan, Heming Huang, Bozhang Dong, Justin Norman, Zeyu Zhang, John Bowers, and Frederic Grillot

Doc ID: 370714 Received 21 Jun 2019; Accepted 01 Aug 2019; Posted 02 Aug 2019  View: PDF

Abstract: This work investigates the dynamic and nonlinear properties of quantum dot (QD) lasers directly grown on silicon with the view of isolator-free applications.Among them, the chirp parameter, also named the aH-factor, is featured through a thermally insensitive method analyzing the residual side-mode dynamics under optical injection locking. The aH at threshold is found as low as 0.32. Then, the nonlinear gain is investigated from the gain compression factor viewpoint. The latter is found higher for epitaxial QD lasers on silicon than that in heterogeneously integrated quantum well (QW) devices on silicon. Despite that, the power dependence of the aH does not lead to a large increase of the chirp coefficient above the laser’s threshold at higher bias. This effect is confirmed from an analytical model and attributed to the strong lasing emission of the ground state transition, which transforms into a critical feedback level as high as -6.5 dB, which is 19 dB higher than a comparable QW laser. Finally, the intensity noise analysis confirms that QD lasers are overdamped oscillators with damping frequencies as large as 33 GHz. Altogether, these features contribute to fundamentally enhance the reflection insensitivity of the epitaxial QD lasers. This last feature is unveiled by the 10 Gbps error-free high-speed transmission experiments. Overall, we believe that this work is of paramount importance for future isolator-free photonics technologies and cost-efficient high-speed transmission systems.

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