Abstract:In this paper, a new method of constructing single-fiber optical tweezers is proposed, which can achieve multi-optical well non-contact capture on the same optical fiber, so as to reduce the difficulty of making single-fiber optical tweezers and enhance the operation function of single-fiber optical tweezers. We use the 650 nm laser source to excite high purity LP11 mode in 980 nm single-mode fiber, which can achieve the multi-optical trap capture effect around the fiber port after simple micro-staggered core fusion treatment for common single-core fiber. Optical fiber ports are fabricated using thermal method to construct special tip structures. Simulation and experimental results show the feasibility of the structure. The excitation and utilization of multi-mode beams in single fiber constitute a new development of single fiber optical trap, enrich the function of single fiber optical tweezers, and make more practical applications in biomedical research possible.

Abstract:A low noise InGaAs/InP single photon avalanche diode (SPAD) is demonstrated. The device is based on planar type separate absorption, grading, charge and multiplication structure. Relying on reasonably designed device structure and low-damage Zn diffusion technology, excellent low-noise performance is achieved. Due to its importance, the physical mechanism of dark count is analyzed through performance characterization at different temperatures. The device can achieve 20% single photon detection efficiency and 320 Hz dark count rate (DCR) with a low after pulsing probability of 0.57% at 233 K.

Abstract:A novel quasi-distributed liquid pressure sensing system based on distributed polarization crosstalk analysis (DPXA) in polarization maintaining fiber (PMF) is proposed and demonstrated. We design a special structure of liquid pressure sensing units and invent a corresponding nonlinear calibration method. Five sensing units deployed on a sensing tape can effectively transform the liquid pressure into the transverse-force applied on the sensing PMF, and the induced polarization crosstalk can be measured and located by the DPXA system, so as to further establish the relationship between liquid pressure and crosstalk through the nonlinear calibration method. The liquid pressure sensing system has good sensitivity and high repeatability, and a maximal measurement relative error of 8.96% is measured for the five sensing units, which can be much improved by optimizing the packaging of sensing units. We believe our sensing system will find great applications in the field of engineering liquid pressure sensing.

Abstract:Consumption of fossil fuel has led to serious environmental pollution, and an urgent demand for solar energy. Perovskite solar cell (PSC) is a device that converts solar energy into electricity. It is cost effective and power efficient, which has attracted much attention. However, PSC shows low absorptivity due to the limited thickness of the active layer. In this paper, a bilateral L-shaped metal grating structure is introduced into the PSC to enhance the absorptivity of the active layer by the surface plasmon effect between the metaling grating and the TiO2. With the deflection angle of the inner angle connection line of the metal grating is 45°, the inner angle distance is 100 nm, and the structural period is 250 nm, the absorptivity of the active layer of the PSC is 86.5% at 715 nm, which is 28.6% higher than the conventional solar cell at the same wavelength. Such results provide an effective way to improve the absorption of PSCs.

Abstract:Frequency-swept interferometry (FSI) is a well-known ranging technique, but it suffers from three problems, namely, the Doppler effect, the frequency-sweep nonlinearity, as well as the slow frequency-sweep rate. The first two problems hinder the measurement accuracy, while the third problem limits the measurement rate. In this paper, we present a dynamic FSI (DFSI) that solves these three fundamental problems simultaneously. The DFSI consists of two auxiliary interferometers (AU1 and AU2) and two measurement interferometers (FSI and frequency-fixed interferometry (FFI)). We use FSI to obtain the Doppler and nonlinearity affected ranging signal, AU1 to monitor the frequency-tuning nonlinearity in the frequency-swept laser (FSL), and FFI and AU2 to constitute a laser vibrometer for monitoring the target motion-induced Doppler effect. Then, a novel signal fusion processing technique is applied to reconstruct the real dynamic distance from the above-measured signals. The dynamic ranging error caused by the Doppler effect and frequency-sweep nonlinearity in FSI can be eliminated and the dynamic distance at each sampling point can be obtained. The validity of this method is demonstrated by numerical experiments.

Abstract:We have successfully demonstrated a stable dual-wavelength Q-switched erbium-doped fiber laser (EDFL) using a single mode fiber-multimode fiber-single mode fiber (SMF-MMF-SMF) structure-based filter. Using a graphene oxide (GO) saturable absorber (SA) to modulate the cavity loss, passive Q-switching of the dual-wavelength laser is achieved at 1 549.6 nm and 1 558.6 nm. The laser recorded the shortest pulse width of about 2.9 μs, the maximum pulse repetition rate of 65.27 kHz and the maximum average output power of 0.99 mW at pump power of 225.1 mW. The present laser has the maximum pulse energy of 15.17 nJ. A 2 SMF-MMF-SMF structure has been experimentally confirmed to be very promising as a wavelength filter.

Abstract:Oscillator circuit has the significant role to always repeat the same signal at the output after certain time interval. In quantum computing, intensity and phase of light signal can be made oscillatory at the output of a quantum optical oscillator circuit. In this paper, we have implemented quantum optical tristate oscillator circuits based on tristate Pauli-X, Y and Z gates using phase and intensity encoding technique of light signal. Here, three different oscillator circuits are developed. The phase of light signal is chosen as the oscillating parameter in all proposed circuits. The truth tables and oscillating phase diagrams are also shown for each oscillator circuit in this paper. The operation of one of the oscillator circuits is simulated with MATLAB to prove its feasibility.

Abstract:ZnO1-xSx thin films modified by sulfur doping were prepared on glass substrates by chemical bath deposition (CBD) for studying the effect of thiourea concentration on the thin film properties. The obtained ZnO1-xSx thin films were characterized by scanning electron microscopy (SEM), which shows the surfaces of ZnO1-xSx thin films deposited under the thiourea concentration of 0.14 M are more compact. X-ray diffraction (XRD) measurement shows that the ZnO1-xSx thin films with hexagonal crystal structure had strong diffraction peaks and better crystallinity. The optical transmittance of the ZnO1-xSx thin films with 0.14 M thiourea concentration is above 80% in the wavelength range of 300—900 nm. According to the measurement results from spectrophotometer, the ZnO1-xSx band gap energy value Eg varies nonlinearly with different S/(S+O) ratio x, and increases with the increase of x. There is a band gap value of 2.97 eV in the ZnO1-xSx thin films deposited under 0.14 M thiourea concentration. Therefore, the thin films have better structural, optical and electric properties, and are more suitable for the buffer layers of copper indium gallium selenide (CIGS) thin film solar cells.

Abstract:Tellurite glasses combined with metal silver nanoparticles (Ag NPs) and Er3+/Tm3+/Ho3+ ions were synthesized using melting and quenching technique, and the enhanced two-band near-infrared (NIR) fluorescence induced by Ag NPs was reported. Upon the excitation of 808 nm laser diode (LD), dual-broadband and flat NIR fluorescence ranging from 1 350 nm to 1 600 nm and from 1 600 nm to 2 200 nm with full width at half maximum (FWHM) of 154 nm and 374 nm respectively in Ag NPs embedded tellurite glass doped with appropriate concentrations of Er3+/Tm3+/Ho3+ ions has an obvious enhancement of about 40% with respect to the glass sample without Ag NPs, which is attributed to the local field effect caused by Ag NPs and energy transfer from Ag species to rare-earth ions. The enhanced dual-broadband and flat NIR fluorescence enables us to develop various NIR band photonic devices flexibly.

Abstract:The time evolution of the quantum entropy in a GaAs/AlAs one-dimensional photonic crystal (1DPC) with an atomic system defect layer is investigated in this work. The entanglement between atomic system and their spontaneous emission fields near the edge of the photonic band gap (PBG) is coherently controlled by the coupling field. Comparison between the atom-photon entanglement of the atomic system in the vacuum surrounding and that near the PBG of the 1DPC shows that the degree of entanglement strongly depends on the PBG. We find that degree of entanglement is strongly dependent on the intensity and detuning of the coupling and probe fields. Furthermore, the effect of the phase difference between applied fields on the atom-photon entanglement is studied. The potentially possible technological applications can be provided by the proposed model in the quantum optics and quantum communications based on photonic crystal.

Abstract:An improved successive cancellation list bit-flip based on assigned set (AS-SCLF) decoding algorithm is proposed to solve the problems that the successive decoding of the successive cancellation (SC) decoder has error propagation and the path extension of the successive cancellation list (SCL) decoder has the decision errors in the traditional cyclic redundancy check aided successive cancellation list (CA-SCL) decoding algorithm. The proposed algorithm constructs the AS firstly. The construction criterion is to use the Gaussian approximation principle to estimate the reliabilities of the polar subchannel and the error probabilities of the bits under SC decoding, and the normalized beliefs of the bits in actual decoding are obtained through the path metric under CA-SCL decoding, thus the error bits containing the SC state are identified and sorted in ascending order of the reliability. Then the SCLF decoding is performed. When the CA-SCL decoding fails for the first time, the decision results on the path of the SC state in the AS are exchanged. The simulation results show that compared with the CA-SCL decoding algorithm, the SCLF decoding algorithm based on the critical set and the decision post-processing decoding algorithm, the improved AS-SCLF decoding algorithm can improve the gain of about 0.29 dB, 0.22 dB and 0.1 dB respectively at the block error rate (BLER) of 10-4 and reduce the number of decoding at the low signal-to-noise ratio (SNR), thus the computational complexity is also reduced.

Abstract:Depth estimation from single fringe pattern is a fundamental task in the field of fringe projection three-dimensional (3D) measurement. Deep learning based on a convolutional neural network (CNN) has attracted more and more attention in fringe projection profilometry (FPP). However, most of the studies focus on complex network architecture to improve the accuracy of depth estimation with deeper and wider network architecture, which takes greater computational and lower speed. In this letter, we propose a simple method to combine wavelet transform and deep learning method for depth estimation from the single fringe pattern. Specially, the fringe pattern is decomposed into low-frequency and high-frequency details by the two-dimensional (2D) wavelet transform, which are used in the CNN network. Experiment results demonstrate that the wavelet-based deep learning method can reduce the computational complexity of the model by 4 times and improve the accuracy of depth estimation. The proposed wavelet-based deep learning models (UNet-Wavelet and hNet-Wavelet) are efficient for depth estimation of single fringe pattern, achieving better performance than the original UNet and hNet models in both qualitative and quantitative evaluation.