Accepted papers to appear in an upcoming issue
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Dispersion Measurement of Ultra-High Numerical Aperture Fibers covering Thulium, Holmium, and Erbium Emission Wavelengths
Piotr Ciacka, Anupamaa Rampur, Alexander Heidt, Thomas Feurer, and Mariusz Klimczak
Doc ID: 324555 Received 21 Feb 2018; Accepted 12 Apr 2018; Posted 13 Apr 2018 View: PDF
Abstract: We present broadband group velocity dispersion (GVD) measurements of commercially available ultra-high numerical aperture fibers (UHNA1, UHNA3, UHNA4, UHNA7 and PM2000D from Coherent-Nufern). Although these fibers are attractive for dispersion management in ultrafast fiber laser systems in the 2 μm wavelength region, experimental dispersion data in literature is scarce and inconsistent. Here we demonstrate the measurements using the spectral interferometry technique covering the typically used erbium, thulium and holmium emission bands. The results are characterized in terms of the standard-deviation uncertainty and compared with previous literature reports. Fitting parameters are provided for each fiber allowing for the straightforward replication of the measured dispersion profiles. This work is intended to facilitate the design of ultrafast fiber laser sources and the investigations of nonlinear optical phenomena.
Optical study of calcium precipitates in additively colored CaF₂ crystals
Aleksandr Angervaks, Andrei Veniaminov, Maksim Stolyarchuk, Vyacheslav Vasilev, Irina Kudryavtseva, Pavel Fedorov, and Aleksandr Ryskin
Doc ID: 325228 Received 01 Mar 2018; Accepted 11 Apr 2018; Posted 13 Apr 2018 View: PDF
Abstract: The absorption spectra and microscopic images of calcium precipitates in CaF₂ crystals additively colored in a heat-pipe set-up at various coloring regimes are studied. The effect of two main parameters of coloring procedure, calcium vapor pressure and temperature, is found to be different. Higher values of both parameters increase the number of anion vacancies and electrons introduced into the crystal at the procedure, hence increasing also the concentration of calcium precipitates formed at the transformation of accumulations of these components. However, the pressure rise results in the concentration growth of calcium ions converted into colloidal particles, while the increase of temperature produces mainly calcium rods. The specific features of a surface layer of colored crystal depending on coloring regime are discussed.
High-efficiency metasurface grating constituted by new Huygens particles with wide tuning ranges of transmission magnitudes and phases
Yang Xu, Nianxi Xu, hai liu, Dongzhi Shan, Naitao Song, and Jinsong Gao
Doc ID: 326183 Received 16 Mar 2018; Accepted 11 Apr 2018; Posted 13 Apr 2018 View: PDF
Abstract: A subwavelength-scale Huygens particle utilizing both electric and magnetic responses is proposed here. As the electric and magnetic responses of the proposed particle are independent of each other, arbitrary complex transmission coefficients covering all magnitudes from 0 to 0.9 and all phases (360o) can be achieved by varying its structural parameters. By properly engineering the distribution of transmission magnitudes and phases, a Huygens metasurface grating with excitation of +1 order harmonic is designed and fabricated. The measurement results are in agreement with the simulations, further demonstrating the validity of designed Huygens particle and metasurface.
Liquid Surface Tension and Refractive Index Measurement by using a Tilted Fiber Bragg Grating
Zexu Liu, Yu Shen, Yike xiao, jiaqi gong, Jianfeng Wang, tingting lang, chunliu zhao, Changqing Huang, yongxing jin, Xinyong Dong, Yang Zhang, Zhenguo Jing, Wei Peng, and Yuliya Semenova
Doc ID: 321088 Received 31 Jan 2018; Accepted 10 Apr 2018; Posted 13 Apr 2018 View: PDF
Abstract: A simultaneous refractive index (RI) and liquid surface tension (ST) (at the level of 10-3 N) measurement system has been proposed by using a 1.8 cm-long, 80-tilted fiber Bragg grating (TFBG). When the TFBG is pulled up from the liquid into the air at a fixed height (corresponding to a fixed contact angle between the fiber and the liquid), the ST acting upon the TFBG depends on the length of the TFBG covered with the liquid film along the fiber axis direction. The liquid film covering the grating results in the shifts of the resonant cladding modes of the TFBG. For the liquid with an RI in the range from 1.33 to 1.44, its RI and ST can be obtained simultaneously through measurement of shifts in the resonant wavelengths and changes of the intensities of the resonant wavelengths dips in the TFBG spectrum by using the known ST and RI of water as a reference.
Stability and Dynamics of Microring Combs: Elliptic function solutions of the Lugiato-Lefever equation
J. Kutz, Chang Sun, and Travis Askham
Doc ID: 314784 Received 01 Dec 2017; Accepted 10 Apr 2018; Posted 11 Apr 2018 View: PDF
Abstract: We consider a new class of periodic solutions to the Lugiato-Lefever equations (LLE) that govern the electromagnetic field in a microresonator cavity. Specifically, we rigorously characterize the stability and dynamics of the Jacobi elliptic function solutions of LLE and show that the $\dn$ solution is stabilized by the pumping of the microresonator. In analogy with soliton perturbation theory, we also derive a microcomb perturbation theory that allows one to consider the effects of physically realizable perturbations on the comb line stability, including effects of Raman scattering and stimulated emission. Our results are verified through full numerical simulations of the LLE cavity dynamics. The perturbation theory gives a simple analytic platform for potentially engineering new resonator designs.
Ultrafast Photocarrier Dynamics in Single-Layer Graphene Driven by Strong Terahertz Pulses
Ali Mousavian, Byounghwak Lee, Andrew Stickel, and Yun-Shik Lee
Doc ID: 319656 Received 12 Jan 2018; Accepted 10 Apr 2018; Posted 11 Apr 2018 View: PDF
Abstract: Time-resolved high-field terahertz (THz) spectroscopy of photoexcited graphene demonstrates extraordinary photocarrier dynamics in single-layer graphene. Strong THz fields and photoexcitation simultaneously enhance the THz transmission of graphene mainly due to the increase of carrier scattering rates. A theoretical analysis confirms that the graphene conductivity undergoes transient decreases to the large extent under the THz and optical excitations, indicating that both the strong THz fields and photoexcitation effectively elevate the carrier scattering rates. The relaxation of photocarriers, on the other hand, shows opposite effects of the THz fields and photoexcitation. Photoexcitation increases the relaxation time via the reabsorption of optical phonons by photocarriers, while strong THz fields reduce the relaxation time because the field induced redistribution of electrons opens up unoccupied states in the conduction band and consequently enhances the relaxation and the phonon emission.
High-precision two- and three-dimensional atom localization via spatial dependent probe absorption in a closed-loop M-type atomic system
Ajay Wasan and Neeraj Singh
Doc ID: 320705 Received 25 Jan 2018; Accepted 10 Apr 2018; Posted 11 Apr 2018 View: PDF
Abstract: We propose a scheme for high-precision two- and three-dimensional atom localization in coherently driven closed-loop five-level M-type atomic system by using a density matrix formalism. Our system not only consists strong and probe fields but also a microwave field to form a close loop in taken atomic system. Due to position-dependent interaction of atom in standing-wave field, the absorption spectra of the probe field provide the precise information about atom localization in a subspace of one wavelength. While numerically solving the density matrix equations, various kinds of localization patterns are obtained such as parallel wave-, crater-, valley-, and bellshape-like in case of two-dimensional atom localization. Further, three-dimensional atom localization case is also discussed under different parametric conditions. High-precession and high-resolution of atom localization are observed for our case and the localization can be tuned to desired subspace by proper adjusting external parameters. Moreover, maximum conditional probability distribution of atom is also achieved, i.e, $1$ in both two- and three-dimensional localization cases under appropriate conditions.
Rate equation reformulation including coherent excitation: application to periodic protocols based on spectral holeburning
Yoann Attal, Perrine Berger, Loic Morvan, Pascale Nouchi, Daniel Dolfi, Thierry Chaneliere, and Anne Louchet-Chauvet
Doc ID: 321016 Received 16 Feb 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018 View: PDF
Abstract: A large number of signal processing protocols are based on recording a spectral pattern via spectral holeburning in an inhomogeneously broadened absorption profile. We present a simulation method specifically designed for periodic excitation sequences leading to the creation of a spectral pattern. This method is applicable to any multilevel atomic structure. The atomic variables' coherent dynamics is solved for a single temporal excitation step. The result is expressed as an equivalent population transfer rate. This way, the whole sequence is described as a matrix product and the steady-state of the system under periodic excitation is easily derived. The propagation through the atomic medium is fully decoupled from the temporal evolution. We apply this method to the engraving of a spectral grating in optically thick Tm:YAG for wideband spectral analysis.
Manipulating group velocity of multi-frequency light in a five-level cascade-type atomic medium associated with giant self-Kerr nonlinearity
Bang Nguyen, Doai Le, and Anh Nguyen Tuan
Doc ID: 319164 Received 08 Jan 2018; Accepted 06 Apr 2018; Posted 11 Apr 2018 View: PDF
Abstract: We proposed a model to manipulate group velocity of a multi-frequency probe light in an electromagnetically induced transparency (EIT) medium consisting of five-level cascade-type atoms associated with a giant self-Kerr nonlinearity. An analytic expression of group index for the probe light is derived as a function of parameters of the probe and coupling fields, atomic density, and life-times of excited atomic states. In the presence of the self-Kerr, both probe and controlling fields can be used as knobs to manipulate the probe light between the subluminal and superluminal propagation modes in three separated frequency regions. The theoretical model agrees with experimental observation, and it is helpful to find the optimized parameters and related applications. Furthermore, using such a cascade excitation scheme it could be possible choose the uppermost excited electronic states having long life-times, as Rydberg states, to slow the light down to few mm/s.
Propagating bound states in the continuum in dielectric gratings
Evgeny Bulgakov, Dmitrii Maksimov, Polina Semina, and Stanislav Skorobogatov
Doc ID: 322886 Received 08 Feb 2018; Accepted 06 Apr 2018; Posted 06 Apr 2018 View: PDF
Abstract: We consider propagating bound states in the continuum in dielectric gratings.The gratings consist of a slab with ridges periodically arrangedether on top or on the both sides of the slab. Based on the Fourier modal approach we recover theleaky zones above the line of light to identify thegeometries of the gratings supporting Bloch bound states propagating in the direction perpendicular tothe ridges. Most importantly, it is demonstrated that if a two-side grating possesses either mirror orglide symmetrythe Bloch bound states are stable to variation of parameters as far as the above symmetries are preserved.
Double-cavity optical bistability and all-optical switching in four-level N-type atomic system
Ren-Gang Wan, Yu-Yuan Chen, and Ya-Nan Li
Doc ID: 323131 Received 12 Feb 2018; Accepted 06 Apr 2018; Posted 06 Apr 2018 View: PDF
Abstract: We analyze the absorptive and hybrid absorptive-dispersive double-cavity optical bistability behavior in a four-level N-type atomic system driven by two optical fields circulating inside two independently unidirectional ring cavities and a trigger field outside the cavities. In this system, the two-photon absorption and cross Kerr nonlinearity play significant roles in the formation of bistability and can be controlled efficiently due to the quantum interference effect, and then the resulted nonlinear behavior exhibits different features from the two/three-level schemes. It is shown that the threshold values and hysteresis cycle width of the bistable curve can be manipulated via the adjustment of the system parameters. Meanwhile, we also obtain double-beam optical multistability. When adding positive and negative pulses to the cavity input, all-optical steady-state switching for the two cavity outputs can be achieved simultaneously. Therefore, the proposed scheme may have potential applications in all-optical communication and computing.
Construction and Floquet-Bloch analysis of analytically solvable Hill equations with smooth potentials
Gregory Morozov, Donald Sprung, and Alexander Ibrahim
Doc ID: 320712 Received 25 Jan 2018; Accepted 04 Apr 2018; Posted 06 Apr 2018 View: PDF
Abstract: We construct analytically solvable Hill equations with smooth potentials and smooth solutions using a method of Wu and Shih. We then use Floquet-Bloch theory to analyze the band structure and find the Floquet-Bloch fundamental system of solutions of the resulting differential equation. Three examples of constructed potentials and their corresponding solutions are worked out.
Constrained Phase Retrieval: when alternating projection meets regularization
Baoshun Shi, Qiusheng Lian, Xin Huang, and Ni An
Doc ID: 318687 Received 02 Jan 2018; Accepted 03 Apr 2018; Posted 11 Apr 2018 View: PDF
Abstract: Simplicity and few parameters needed to be tuned by hand are the main advantages of alternating projection (AP) methods, a fundamental class of phase retrieval (PR) methods in optical imaging field. However, AP methods often suffer from low-quality imaging when few diffraction patterns are recorded. Regularized PR methods avoid this deficiency by using some proper regularization models, but many manually chosen parameters are needed. In this work, we propose a novel unified framework called constrained PR (ConPR), which brings the AP method and the regularization approach together. The proposed ConPR framework not only can perform high-quality imaging from few diffraction patterns, but also does not need extra hand-tuned parameter. Our proposed generalized constrained PR optimization model consists of a relation function term, a regularization term and a measurement constraint. The measurement constraint ensures that the recovered image matches with the measurement, and the regularization term can impose some desirable properties on the recovered image. The relation function promotes the approximation of the two underlying variables. The sparsity under the BM3D (block-matching and 3-D filtering) frame is incorporated into the proposed ConPR framework, which yields an image updating sub-problem and a constrained optimization sub-problem. The epigragh set of the data fidelity function is defined, and the constrained optimization sub-problem is solved via the epigragh concept. Diffraction imaging from one noisy coded diffraction pattern (CDP) demonstrates the effectiveness of our proposed ConPR algorithm. Most importantly, since the default parameters are utilized in BM3D, no additional parameter in ConPR is needed to be tuned by hand.
Computation of the timing jitter, phase jitter and linewidth of a similariton laser
John Zweck and Curtis Menyuk
Doc ID: 318390 Received 26 Dec 2017; Accepted 03 Apr 2018; Posted 03 Apr 2018 View: PDF
Abstract: We derive a formula for the power spectral density of the frequency comb generated by a fiber laser in terms of the power spectrum of the noise-free optical pulse, the timing jitter, and the phase jitter. We provide the first computational study of phase jitter and comb linewidths in a nonsolitonic fiber laser with large changes in the pulse each round trip. For fiber lasers operating in or near the similariton regime, we investigate how the pulse parameters and noise performance depend on the system parameters.Across a large dispersion range, the dechirped pulsewidth, timing jitter, phase jitter, and comb linewidths are smaller when the gain in the optical amplifier is larger. Over a narrow range of negative dispersion values near zero, the timing jitter and comb linewidths are smaller with a wider optical filter. However, with the wider optical filter, the pulsewidth increases significantly and the noise performance deteriorates rapidly as the dispersion increases above zero. These trends are in general agreement with experimental studies of timing jitter and the linewidth of the carrier-envelope offset frequency in Yb-fiber lasers, and are consistent with the Namiki-Haus theory of timing jitter in a stretched-pulse laser.
Semiconductor-based far-infrared biosensor by optical control of light propagation using THz metamaterial
Zohreh Vafapour and Hossain Ghahraloud
Doc ID: 320821 Received 31 Jan 2018; Accepted 03 Apr 2018; Posted 04 Apr 2018 View: PDF
Abstract: By incorporating a dielectric material into a semiconductor thin film, we have demonstrated an optically reconfigurable a classical electromagnetically induced reflectance (Cl-EIR) effect in planar metamaterials (MMs)functioning at far-infrared (far-IR) frequency regime. The proposed far-IR sensor is a micro structure composed of a semiconductor thin film and three dielectric antennas. Numerical analysis based on the far and near field interaction are investigated in detail. The coupling between the subradiant and supperradiant modes verify the existence of the Cl-EIR effect. TheCl-EIR frequency could be tuned by changing the surrounding medium, the temperature of the semiconductor layer, the semiconductor material, and the substrate material. Therefore, the proposed complementary MM micro structure, based on semiconductor featuring tunable reflectance windows, may open up new avenues for designing tunable temperature sensors, optical and biomedical sensors, switches, and slow light devices.
Sturmian-Floquet approach to high-order harmonic generation
József Kasza, Peter Dombi, and Peter Földi
Doc ID: 312515 Received 01 Nov 2017; Accepted 27 Mar 2018; Posted 30 Mar 2018 View: PDF
Abstract: We show that the Floquet approach with aSturmian basis means an efficient description of high-order harmonic generation with monochromatic excitation. This method, although involves numerical calculations, is close to analytic approaches with the corresponding deeper insight into the dynamics. As a first application, we investigate the role of atomic coherence during the process of HHG: as it is shown, different coherent superpositions of initial atomic states produce observably different HHG spectra. For linearly polarized excitation, we demonstrate that the question whether the constituents of the initial superpositions are dipole coupled or not, strongly influences the dynamics. By investigating time-dependent HHG signals, we also show that the preparation of the initial atomic state can be used for the control of the high-harmonic radiation.
Time-wavelength optical sampling spectroscopy based on dynamic laser cavity tuning
SRIKAMAL SOUNDARARAJAN, Lin Yang, SHUQIN ZHANG, HEMANG JANI, and Lingze Duan
Doc ID: 321036 Received 31 Jan 2018; Accepted 26 Mar 2018; Posted 30 Mar 2018 View: PDF
Abstract: Time-wavelength optical sampling (TWOS) is proposed here as a scheme that leverages the advantages of both wavelength-time mapping and ultrafast optical sampling to achieve real-time spectral measurement with simple configurations and slow photodetectors. As a proof of concept, a TWOS spectrometer based on dynamic optical sampling by laser cavity tuning is developed. Real-time absorption spectroscopy with a 0.3-nm spectral resolution and a 60-nm total spectral range (laser-limited) is demonstrated at an 150-Hz updating rate. Theoretical analysis and practical limiting factors are discussed in detail. Potential applications of TWOS include spectroscopy, imaging, metrology, and optical sensing.
Broadband in-line terahertz 2D imaging: copmparative study with time-of-flight, cross-correlation and Fourier transform data processing
Alexander Ushakov, Pavel Chizhov, Vladimir Bukin, Andrei Savel'ev, and Sergey Garnov
Doc ID: 314655 Received 28 Dec 2017; Accepted 21 Mar 2018; Posted 22 Mar 2018 View: PDF
Abstract: A pulsed broadband (from 0.1 to 1.5 THz) in-line terahertz (THz) time domain electro-optical sampling is applied for the visualization of phase objects by using a large aperture electro-optical crystal (ZnTe, 1x1 cm2). The waveforms of THz pulses are generated in a lithium niobate (LiNbO3) crystal pumped by femtosecond pulses with tilted amplitude front, and measured by a 2D THz imaging system. This system depicts the object under study in the THz range via PTFE lens in 2F-2F geometry onto the ZnTe crystal and then images the crystal surface on a CMOS camera using electro-optical sampling. The reconstruction of the image in such a scheme is implemented by processing the received 3D spatial-temporal distributions of the THz field in three different ways: (i) by detecting displacement of the maximum peak position of the THz pulse due to phase delay in the object under study; (ii) by using a cross-correlation function analysis; (iii) by a Fourier transformation of a THz waveform and subsequent extraction the phase difference at each THz frequency. Images of transparent PTFE objects were obtained. Main features of the resulting imaging system are discussed.
A concise relation among the TE₀₁ mode of the metal rectangular waveguide and the TE₁ and TM₀ modes of the metal parallel-plate waveguide for terahertz waves
Qing Cao, Pengcheng Shen, lihua bai, Kai Wang, Dengming Wu, and Zhe Li
Doc ID: 315843 Received 15 Dec 2017; Accepted 21 Mar 2018; Posted 22 Mar 2018 View: PDF
Abstract: For terahertz waves, we analytically present a concise relation of the effective indices among the TE₀₁ mode of the metal rectangular waveguides, the TE₁ mode and the TM₀ mode of the infinite metal parallel-plate waveguides. In the assumption that the modal field in the metal rectangular waveguide is linearly polarized and separable, the effective index of the TE₀₁ mode can be obtained from the combination of the effective indices of the associated TE₁ mode and TM₀ mode. We further find that the real part of the effective index of the TE₀₁ mode is mainly determined by that of the TE₁ mode, while, for the imaginary part, TM₀ mode dominates.
Enhanced THz radiation from beating of two Cosh-Gaussian laser beams in a wiggler-assisted collisional magnetized plasma
Mehdi Abedi-Varaki and Saed Jafari
Doc ID: 319184 Received 10 Jan 2018; Accepted 21 Mar 2018; Posted 22 Mar 2018 View: PDF
Abstract: In this paper, the terahertz (THz) radiation generated by mixing of two Cosh-Gaussian laser beams in collisional magnetized plasma has been studied in the presence of a helical magnetostatic wiggler. Equations governing to THz radiation generation of laser beam and efficiency of emitted radiation for both the left- and right-hand circularly polarizations have been derived. Furthermore, the effects of the THz field amplitude and laser electric field magnitude for different wiggler strengths and decentered parameters have been investigated. Numerical results indicate that the amplitude of THz electric field radiation increases with the increasing wiggler frequency, and consequently THz radiation becomes stronger. Moreover, it is seen that normalized laser efficiency has a decreasing trend with increasing normalized collision frequency for different wiggler magnetic field strength. Furthermore, it is found that the efficiency for left-hand circularly polarized wave in large wiggler frequency is smaller than right-hand circularly polarized wave. It is also shown that when decentered parameters are altered from zero to 0.8, the THz field amplitude has a maximum point in 0.65 and when values of decentered parameters are changed from 0.8 up to about 2, increase of decentered parameters leads to advent two maximum points in THz field amplitude. Finally, by employing large decentered parameters and suitable wiggler magnetic field frequency the efficiency of order 50% in right-hand polarization can be obtained.
Light harvesting optimization in two-dimensional TMDC monolayer heterostructures
Narges Ansari and Farinaz Ghorbani
Doc ID: 315307 Received 11 Dec 2017; Accepted 14 Mar 2018; Posted 16 Mar 2018 View: PDF
Abstract: Heterostructures of two-dimensional transition metal dichalcogenides (TMDCs) have recently received upsurge attention for application in optoelectronics. In this paper, we demonstrate efficient absorber heterostructures in a form of air/hetero-TMDCs/substrate with various TMDC monolayers (MoSe₂, WSe₂, MoS₂ and WS₂). The dielectric permittivity of individual TMDC monolayers is determined using the Lorentz model. The absorption response of designed hetero-TMDCs is determined by using the transfer matrix method (TMM). The effects of light polarization, angle of incident and substrate on the absorption response are investigated. Finally, MoSe₂/MoS₂ and WS₂/MoSe₂ heterostructures on the SiO₂ (90 nm)/Si substrate are found to have absorption over 30% in a broadband wavelength range and in a wide incident angle, both useful designs for optoelectronic applications.
Entangled multi-mode spin coherent states of trapped ions
Yusef Maleki and Alireza Maleki
Doc ID: 315874 Received 18 Dec 2017; Accepted 13 Feb 2018; Posted 16 Feb 2018 View: PDF
Abstract: Multi-mode macroscopic states consisting of asuperposition of spin coherent states that are generated in a trapped ion system are introduced. The role of various parameters that control the entanglement of the system are exposed and their effects are quantified.In particular, it is shown that the generated states exhibit different entanglement characteristics for odd and even $2nj$, where jis the spin of each mode and $n$ is the number of modes.