查看更多>>摘要：? 2021 Elsevier B.V.Stable bound pulses (BPs) are numerically obtained in an all-normal-dispersion fiber laser (ANDFL) using white noise as the initial field. When the pump power is monotonically increased, a rhythmic behavior of the number of dissipative solitons (DSs) is first discovered. In addition, we have also observed the soliton explosion in the build-up process of BPs and found that for the same number of pulses, the higher pump power would trigger more frequent soliton explosions. The rule of the rhythmic behavior of DSs number with the pump power may provide new insights into the formation and evolution of DSs. These phenomena also contribute to an in-depth understanding of BPs dynamics and enrich DS dynamics.
查看更多>>摘要：? 2021 Elsevier B.V.In this paper, a new structure of nanoantenna has been designed, which uses a kind of Epsilon-Near-Zero (ENZ) material film (Indium Tin Oxide, ITO) and trapezoid metal to achieve high absorption (above 90%) effect for the incident light between 1310 nm and 1550 nm of the wavelength. The results have been put to the proof with the method of Finite Difference Time Domain (FDTD) Solutions. The nanoantenna we design can be applied to single photon detectors of which operating wavelength are 1310 nm or 1550 nm. Meanwhile, by tuning the carrier concentration of ITO, the operating range of the nanoantenna can be changed, which further upgrades the practicability of the nanoantenna.
查看更多>>摘要：? 2021 Elsevier B.V.We present a stable microwave local oscillator (LO) distribution scheme based on a phase-locked optoelectronic oscillator (OEO) assisted by passive compensation. By injecting the LO reference into the phase-locked OEO and locking it with the oscillation signal, a microwave LO with a low phase noise can be tapped at the remote site. Meanwhile, a frequency-mixing-based passive compensation system is utilized to efficiently prevent the remote LO signal from the slow phase drift caused by the temperature susceptibility of fiber. In the experiment, a 10.8 GHz LO signal is stably distributed along a 6.8-km ring fiber to the remote site that is 1.8 km away from the local site. The frequency stability of 3.8 × 10?14 at 1s and 2.3 × 10?17 at 10000 s can be attained. The single-sideband (SSB) phase noise of the received signal at the remote site is up to –110 dBc/Hz at 10 kHz offset frequency with the root-mean-square phase jitter of 0.023 rad.
查看更多>>摘要：? 2021 Elsevier B.V.With the development of high-speed and large-capacity optical fiber communication technology, nonlinear damage has been one great obstacle to the development of optical fiber communication. Transmission distance and signal energy are two main factors that affect the nonlinear damage. The nonlinear compensation algorithm based on perturbation theory can compensate nonlinear damage. However, the coefficients of perturbation matrix cannot be calculated easily. In this paper, we make use of machine learning as a tool, propose an equalizer with support vector regression based on perturbation theory. For a 120 Gb/s, 375 km transmission distance, dual-polarization 64 quadrature amplitude modulation communication system, bit error ratio (BER) is lower than hard-decision forward error correction threshold 3.8×10?3 in the launched optical power (LOP) from -4 dBm to 3 dBm and when LOP is 1 dBm, BER is lower than forward error correction threshold 1.0×10?3. Moreover, it is shown that the optimum LOP is increased by 2 dB.
查看更多>>摘要：? 2021 Elsevier B.V.The creation of vortex beams becomes increasingly important in microwave region for their potential applications in high-capacity multiplexed wireless communication systems. In this paper, we propose a kind of split-square-ring metasurface for generating microwave vortex beams at 16 GHz. We first analyze the S-parameter of the meta-atoms and then optimize and pick up 8 units which can cover 2π phase shift for the whole array design. Four metasurfaces carrying topological charges from 1 to 4 are, respectively, designed, and full-wave simulation is utilized for evaluating the near-field performance. The orbital angular momentum purity for each topological charge is calculated. Meanwhile, the far-field property has also been simulated and measured, and the simulation results agree well with those in experiments. Our metasurface device provides a flexible way for generating high-quality vortex beams in the microwave region.
查看更多>>摘要：? 2021 Elsevier B.V.The autofocusing Airy beams carrying a new kind of power-exponent phase are proposed and demonstrated experimentally in this paper. The physical mechanism of the proposed beams is theoretically analyzed by using energy flow and phase distribution. Moreover, the influence of the beam parameters on the light intensity distribution and orbital angular momentum is also discussed. The proposed Airy beams with new kind of power-exponent-phase vortices are expected to be useful for the extended applications of optical vortices, particularly for particle trapping.
查看更多>>摘要：? 2021 Elsevier B.V.A silicon cross-coupled double-ring resonator system is proposed and fabricated for an optical multistability application, which consists of a racetrack resonator, a cross-coupled microring and a feedback U-shape waveguide. Transfer matrix method and rigorous simulation is used to analyze the static property. The measured device transmission spectrum can be modulated by applying a voltage to the microheater above the feedback waveguide, coinciding well with the theoretical expectation. With increase and decrease the input light power, optical multistability can be observed, which may be explained with consideration of the two-photon absorption and Kerr nonlinear effect. The presented device shows a favorable design freedom and energy consumption, which could be widely applied in optical logic gates and all-optical signal processing.
查看更多>>摘要：? 2021Digital holographic microscopy is a high-precision, high-resolution quantitative detection method, however, aberration compensation significantly increases the data processing time. We herein propose a method based on sequential shift and a differential–integral algorithm to compensate for fast phase aberrations. The proposed method obtains the phase derivative of the real sample phase information through holograms at different positions and then reconstructs the aberration-free phase result through integration. The compensation avoids complex phase polynomial fitting calculations or optimization iterations, achieves extremely fast aberration compensation, and can theoretically eliminate various low and high-order aberrations, including extremely complex aberrations. We experimentally validate the effectiveness and high speed of the proposed method by imaging paramecium samples.
查看更多>>摘要：? 2021 Elsevier B.V.Fringe projection profilometry (FPP) usually uses a projector with an instable light source due to the unsatisfactory driving power. As a result of the fluctuations of the projection light source, the fringe captured by a camera deviates from its ideal distribution, from which, the calculated phase has a random phase error, thus reducing the 3-D measurement accuracy. We found that the random phase error influences both the system calibration and the 3-D reconstruction, where the influence on the system calibration has not been previously noticed. In this paper, we formulate the phase error model of the phase-shifting algorithm caused by the fluctuations of the projection light source, and analyze its interference on calibration and reconstruction, respectively. From which, an accurate FPP using a combination of accurate calibration and accurate 3-D reconstruction is proposed, which are performed by using a deep learning-based phase calculation method. The provided experimental results verify that the proposed FPP can obviously improve the measurement accuracy.
查看更多>>摘要：? 2021 Elsevier B.V.We present a novel hole-assisted elliptical-core polarization-maintaining few-mode fiber (EC-PM-FMF) composed of three layers of air holes. The proposed fiber breaks degeneracy of modes by introducing geometry asymmetry. Through optimizing the parameters, the designed fiber could support 18 separate polarization-maintaining modes with the minimum effective refractive index difference (Δneff) between adjacent modes larger than 1.21 × 10?4 over the whole C + L band. Moreover, the designed fiber exhibits good mode and propagation properties including large effective mode area, low nonlinear coefficient, small and flat chromatic dispersion, low confinement loss and bending loss. Thus, the fiber can be used in mode division multiplexing (MDM) system without multi-input multi-output (MIMO) digital signal processing (DSP) technology to improve channel utilization.
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