In this paper, a plate shape perception technique based on quasi-distributed fiber Bragg grating (FBG) array and space surface reconstruction algorithm is proposed. Firstly, in order to make curvature continuous, the bicubic plane interpolation algorithm is studied. Then, taking the simulated satellite bulkhead structure as the research object, we research the space surface reconstruction algorithm based on orthogonal curvature and coordinate transformation (translation and rotation). Finally, a four-sided fixed plate deformation monitoring system based on quasi-distributed FBG sensors network and surface reconstruction algorithm is built. Many experiments are conducted to verify the reliability and accuracy of the algorithm. The proposed algorithm provides a new method for three-dimensional reconstruction of spacecraft structure.

Off-axis FBG simulations were performed in this paper using a finite element method in conjunction with the conformal mapping technique to study the bending sensing characteristics of the off-axis FBG with high index modulation. The refractive index (RI) increase of the grating region is taken into consideration for the mode field simulation. The influences of high RI increase and the offset distance of the grating on the bending sensitivity were analyzed. Off-axis FBGs with different offset distances were fabricated using femtosecond laser with phase mask technique in standard single-mode fiber. The simulation results were verified by the experiment. A bending sensitivity of 0.055 dB/m-1 was achieved with an offset distance of 4 μm. The simulation and experiment results suggest that the grating offset distance has a greater influence on the sensitivity of the off-axis FBG with high RI modulation than that with low RI modulation. The proposed sensor structure and simulation results can provide suggestion for the design and processing of off-axis FBG bending sensors.

We proposed a surface plasmon resonance (SPR) refractive index sensor based on hollow-core anti-resonance fiber (HC-ARF). Gold was filled in two symmetric cladding tubes of the fiber, while the analyte was filled in central air holes. The sensing performance was investigated by the finite element method (FEM). Results show that two resonance peaks (a crossing point around 1 030 nm and an anti-crossing region around 1 065 nm) appear for x-polarization (x-pol) core mode coupling with the surface plasmon polariton (SPP) mode. Moreover, the sensitivity was also analyzed. The sensitivity increased with the increase of cladding tube thickness t. The sensor with thickness t=1.7 μm gave a wavelength sensitivity of 7 350—14 790 nm/RIU in the refractive index range of 1.33—1.45 with resonance wavelength from 1 900 nm to 450 nm. Meanwhile, the resolution of 10-6 RIU was achieved. Thanks to high sensitivity and resolution, the proposed sensor has potential applications in glucose detection.

A leaky-wave antenna (LWA) supporting wide-band and continuous-beam scanning is proposed in this paper. It is based on a spoof surface plasmon polariton (SSPP) transmission line (TL) periodically loaded with circular patches. The optimized antenna structure enables its continuous-beam scanning of 69° from backward through broadside to forward with a stable high radiation gain as the operating frequency increases from 7 GHZ to 15 GHz (with a relative bandwidth of 72.73%). Furthermore, a perfect electronic conductor (PEC) reflector is added at a distance of about 0.3λ0 (λ0 is the vacuum wavelength for the broadside radiation) to improve the antenna gain, achieving a gain increase of about 3 dB. The proposed LWA is expected to find applications in planar wireless communication systems.

ZnO1-xSx films were prepared by chemical bath deposition (CBD) on glass substrate. The effects of ammonia concentration on the structure characteristics of ZnO1-xSx films were studied. The results of scanning electron microscope (SEM) show that the film has good density when the concentration of ammonia is 0.4 M. Because more S2- ions are involved in the reaction and less precipitates are generated, the film is relatively dense. The distribution of the film element shows that the growth rate of the film first accelerates and then slows down as the concentration of ammonia increases. X-ray diffraction (XRD) study shows that the diffraction peak is obvious when the ammonia concentration is 0.4 M, and the crystallinity of the film is good. Ultraviolet (UV) spectrophotometer test results show that the ratio of S content (x) and optical band gap (Eg) satisfies Eg(x)=3.325 7x2?2.718 7x+4.357 6. Increasing S content can increase the optical band gap of the film, and increasing ammonia concentration can improve the absorbance of the film, but both have good transmittance. At the ammonia concentration of 0.4 M, the absorbance of the film is good in the wavelength range of 300—900 nm, the transmission rate reaches 80%, and the band gap is 3.75 eV, which is suitable for the buffer layer of solar cells.

In order to increase the number of amplified azimuthal modes in Yb-doped fiber (YDF), a multiple azimuthal modes amplifier based on a ring-core Yb-doped fiber (RC-YDF) was proposed and demonstrated. A home-made RC-YDF which can support 6 azimuthal mode groups was employed to amplify the signal mode at 1 064 nm, using a core pump scheme. The amplification characteristics of 5 high-order azimuthal linear polarization (HA-LP) mode groups (LP11, LP21, LP31, LP41, LP51) were studied comprehensively. A more than 8 dB gain is obtained for each signal mode with 5 dBm input power, and the associated differential modal gain between all modes is less than 1 dB. The intensity profiles of all modes are stable and well preserved during the process of amplification.

Information leakage, which damages the transmission medium in optical communication systems, is becoming increasingly serious. The existing optical communication systems can easily expose data to unauthorized users, specifically when malicious users control the target demodulator. Therefore, based on the alliance chain, the data are encrypted first based on the elliptic curve encryption algorithm and the signature algorithm, and then they are transmitted through the optical network system. Thus, a blockchain-based optical communication security transmission system scheme is proposed. The scheme has a high modulation and demodulation efficiency, fast operation speed, and verifiability. The theoretical analysis and experimental results indicate that the scheme has better security and high performance, and it generates the security requirements of optical communication systems during data transmission.

Based on the nonlinear and mode coupling effect in few-mode photonic crystal fiber (FM-PCF), an approach for supercontinuum (SC) generation in the mid-infrared (MIR) region is proposed. The propagation characteristics of Ge11.5As24Se64.5 FM-PCF have been analyzed and optimized by the full-vector finite element method. The two-mode generalized nonlinear Schrodinger equation (TM-GNLSE) is set up, and the SC generation has been analyzed by the split-step Fourier method. The SC from 1.80 μm to 11.32 μm is generated by pumping 3.0-cm-long fiber at the central wavelength of 3.0 μm, the peak power of 120 W, and the pulse duration of 250 fs.

The nonlinear distortion caused by the Mach-Zehnder modulator (MZM) is one of the main limiting factors for the improvement of the transmission performance of the intensity modulation and direct detection (IM/DD) optical communication system. In order to solve the problem, an improved Volterra nonlinear equalization (VNLE) method is proposed. Compared with the traditional VNLE that uses the least mean square (LMS) to calculate the tap coefficients, the improved VNLE uses the least square (LS) method to obtain more stable convergence. The simulation results show that the VNLE based on LS has better performance when solving complex nonlinear damage. For 25 Gbaud 4-level pulse amplitude modulation (PAM4) signals, the improved VNLE can reduce the bit error rate (BER) to below 10-4 in a 7-km-long single-mode optical fiber transmission system. In addition, in order to make the BER below 10-3, the transmission distance that the improved VNLE can withstand is about 1.5 km longer than that of the traditional VNLE.

The detection of the jet temperature field in an aircraft engine tail is an effective way to reflect the running state of an engine. To solve the complicated detection process of current laser diagnostic methods, the colored background oriented Schlieren (CBOS) method was proposed to obtain a tail jet temperature field. First, the background Schlieren image with three-color points was collected for the exhaust gas temperature (EGT) field of the engine. Then the refractive index field of the engine exhaust was obtained according to the proposed CBOS method. Finally, the three-dimensional EGT field was reconstructed through the refractive index field. The simulation and the experimental results show the feasibility and effectiveness of the proposed method.

A method of detecting chemical oxygen demand (COD) of water based on ultraviolet (UV) absorption spectra is proposed. The modeling and analysis of the standard samples and the actual water samples are carried out respectively. For the standard solution samples, the univariate linear models based on single wavelengths and the partial least square (PLS) model based on synergy interval partial least square (SiPLS) and moving window partial least square (MWPLS) are established. For the actual water samples, different pre-processing methods are used. SiPLS and MWPLS are used to select the characteristic bands. The least squares support vector machine algorithm optimized by particle swarm optimization (PSO-LSSVM) algorithm is used to establish the prediction model, and the prediction results of various models are compared. The results show that the optimal model is PSO-LSSVM which uses SiPLS to select the characteristic bands of the first derivative spectra (preprocessing method). The determination coefficient of the prediction set is 0.963 1, and the root mean square error of prediction (RMSEP) is 2.225 4 mg/L. PSO-LSSVM algorithm has good prediction performance for the analysis of COD in actual water samples by UV spectra. This paper provides a new design idea for the research and development of water quality detection optical sensor.