Abstract:An all-fiber temperature and curvature sensor based on Mach-Zehnder interferometer (MZI) was proposed. The MZI was a sandwich structure which is composed of ring-core fiber (RCF), no-core fiber (NCF) and single-mode fiber (SMF). The temperature and curvature can be demodulated by the wavelength shift and the intensity variation of the dips respectively in the transmission spectrum. The measurement results show that the sensitivity of curvature is −7.88 dBm/m-1 in the range from 3.0 m-1 to 4.2 m-1 and the sensitivity of temperature is 53.5 pm/°C in the range from 60 °C to 200 °C. In addition, the cascaded FBG in the proposed structure, also sensitive to temperature, was used to monitor the fluctuation of temperature. The compact structure, the real-time temperature and the high curvature sensitivity make the sensor have the potential in the field of construction health monitoring and mining safety production.

Abstract:We report an experimental phenomenon of the splitting and merging of the bright-dark pulses (BDPs) in a mode-locked thulium/holmium co-doped fiber laser (THDFL) based on nonlinear polarization rotation (NPR). By adding 100-m-long highly nonlinear fiber (HNLF) into a simple ring cavity, the BDPs can be generated. The time interval between the bright and dark pulses increases linearly with the pump power and approximately equals to the inverse of the modulation frequency of the radio frequency (RF) spectrum. Apart from that, the bright and dark pulses are shown not to be orthogonally polarized. The obtained results are valuable for the evolutionary mechanism of the BDPs in passively mode-locked fiber lasers (PMLFLs).

Abstract:In this paper, a dual-band and reflective polarization converter based on metasurface is proposed. Its unit cell is composed of two layers of metal plates separated by a dielectric substrate. The simulation results show that the proposed converter is able to convert x- or y-polarized incident waves into cross-polarized waves perfectly in frequency bands of 6.75—10.59 GHz and 17.78—19.61 GHz, and the polarization conversion ratio (PCR) is nearly 100%, which can also convert linearly polarized waves into circularly polarized waves at four frequencies. It can be widely used in applications of radar satellites, antenna design and telecommunication with the function of realizing polarization conversion in two bands and achieving high PCR simultaneously.

Abstract:This letter proposes a novel high dynamic range (HDR) pixel using lateral overflow integration capacitor (LOFIC) and adaptive feedback structure. Through detailed analysis of the voltage feedback mechanism, the conversion gain (CG), full well capacity (FWC) and dynamic range (DR) performances of the feedback LOFIC pixel are analytically expressed. The verification results reveal that the equivalent FWC of the feedback LOFIC pixel is 1.89 times of conventional LOFIC pixel, and the DR extension is 5.5 dB. Based on 110 nm CMOS process, a 5.0 μm pixel layout is presented, using 13.3 fF capacitance to achieve 83 ke- FWC and 102.8 dB DR, which are 44 ke- and 97.3 dB of conventional LOFIC pixel under the same design conditions. This also demonstrates that the feedback LOFIC pixel can reduce the dependence of extended DR on capacitor area, and can be used as a reference for HDR pixels design.

Abstract:To address the driving power and density of wavelength-division-multiplexing (WDM) computing architectures, a Fano resonator based on a photonic crystal nanobeam is proposed. The Fano resonator comprises a T-shaped waveguide, introducing an additional phase shift in the continuous propagation mode, and a photonic crystal nanobeam with a discrete mode. The device has one resonance peak within wavelength ranging from 1 500 nm to 1 600 nm, with a maximum extinction ratio of 8.7 dB and a transmission spectrum slope of up to 11.30 dB/nm. The device has good reusability, extinction ratio, and spectral resolution. It is expected to provide essential photonic components for low-energy consumption and high-density photonic computing to meet the requirements of future convolutional neural network (CNN) acceleration computing.

Abstract:With the rapid development of the fifth-generation (5G) wireless system, the explosive growth of transmitted data raises higher requirements for high-performance surface acoustic wave (SAW) devices as filters and duplexers. (100) AlN/(100) ZnO/diamond layered structures are theoretically simulated by finite element method (FEM) to investigate the Rayleigh SAW propagation properties, including phase velocity, electromechanical coupling coefficient K2, and temperature coefficient of frequency (TCF). Three types of layered structures with different interdigital transducers (IDTs) arrangements, which are IDTs/(100) AlN/(100) ZnO/diamond, (100) AlN/IDTs/(100) ZnO/diamond, and (100) AlN/(100) ZnO/IDTs/diamond structures, are considered in the simulations. The results show that the Sezawa mode exhibits larger K2 than the other modes. We found that the (100) AlN/IDTs/(100) ZnO/diamond structure exhibited better SAW properties, including high K2 and appropriate phase velocity.

Abstract:We propose a density-matrix-formalism based scheme to study polarization mode dispersion (PMD) monitoring and compensation in optical fiber communication systems. Compared to traditional monitoring and compensation schemes based on the PMD vector in the Stokes space, the scheme we proposed requires no auxiliary matrices and can be handily extended to any higher-dimensional modal space, which is advantageous in mode-division multiplexing (MDM) systems. A 28 GBaud polarization division multiplexing quadrature phase-shift keying (PDM-QPSK) coherent simulation system is built to demonstrate that our scheme can implement the monitoring and compensation of 170 ps large differential-group-delay (DGD) that far exceeds the typical DGDs in practical optical communication systems. The results verify the effectiveness of the density-matrix-formalism based scheme in PMD monitoring and compensation, thus pave the way for further applications of the scheme in more general MDM optical communication systems.

Abstract:A large mode area multi-core orbital angular momentum (OAM) transmission fiber is designed and optimized by neural network and optimization algorithms. The neural network model has been established first to predict the optical properties of multi-core OAM transmission fibers with high accuracy and speed, including mode area, nonlinear coefficient, purity, dispersion, and effective index difference. Then the trained neural network model is combined with different particle swarm optimization (PSO) algorithms for automatic iterative optimization of multi-core structures respectively. Due to the structural advantages of multi-core fiber and the automatic optimization process, we designed a number of multi-core structures with high OAM mode purity (>95%) and ultra-large mode area (>3 000 μm2), which is larger by more than an order of magnitude compared to the conventional ring-core OAM transmission fibers.

Abstract:A photonic sensor with radio frequency (RF) power detection for body pressure monitoring is proposed. The sensor based on two fiber Bragg gratings (FBGs) can transfer the wavelength shift to the change of RF power. The pressure can be measured by modulating and processing one single frequency RF signal. The theoretical analysis and experimental results of the photonic sensor are presented and discussed. The pressure sensitivities are acquired with 2.62´10-5 mW/kPa at 2.14 GHz, 2.46´10-5 mW/kPa at 2.21 GHz, 2.81´10-5 mW/kPa at 2.37 GHz, and 3.02´10-5 mW/kPa at 2.45 GHz, respectively. Furthermore, the pressure measurements of pressed body parts are also obtained by the sensor.

Abstract:Specular highlight usually causes serious information degradation, which leads to the failure of many computer vision algorithms. We have proposed a novel bifurcated convolution neural network to tackle the problem of high reflectivity image information degradation. A two-stage process is proposed for the extraction and elimination of the specular highlight features, with the procedure starting at a coarse level and progressing towards a finer level, to ensure the generated diffuse images are less affected by visual artifacts and information distortions. A bifurcated feature selection module is designed to remove the specular highlight features, thereby enhancing the detection capability of the network. The experiments on two types of challenging datasets demonstrate that our method outperforms state-of-the-art approaches for specular highlight detection and removal. The effectiveness of the proposed bifurcated feature selection module and the overall network is also verified.

Abstract:Aiming at the problems of low reconstruction quality, poor robustness, and the inability to quickly and stably converge caused by the ill-posedness of electrical capacitance tomography image reconstruction, an improved algorithm based on iterative Tikhonov regularization (ITR) was proposed. The algorithm constructs a new objective function by introducing the Lp norm to carry out multi-criteria constraints, and introduces the result of the corrected Tikhonov regularization (TR) algorithm into the image reconstruction process together with the logarithmic weight factor as the estimated value. At the same time, an acceleration strategy is used, and the residual term is exponentially filtered. Perform ablation, initial value sensitivity, convergence, and noise interference experiments on the improved algorithm and compare it with other common algorithms. Experimental results show that the improved algorithm can quickly and stably converge and has good robustness and initial value insensitivity. The reconstructed image quality is high, the average correlation coefficient (CC) can reach 0.963 3, and the average relative error (RE) can be reduced to 0.069 4.