Modal cross coupling frequently occurs in modal approaches from wavefront gradient data such as lateral shearing measurement through Zernike circle polynomials, since the gradients of Zernike circle polynomials are not orthogonal. We use a modal approaches incorporating the Gram matrix, using the orthogonality of angular derivative of m≠0 modes with respect to weight function w(ρ)=ρ (polar coordinates), and the orthogonality of radial derivative of m=0 modes with respect to weight function w(ρ)=ρ(1-ρ2) (polar coordinates). The Gram matrix method needs no auxiliary vector functions. The Zernike coefficients can be obtained with no modal cross coupling. The simulation results are given, which indicate that the modal cross coupling is avoided by using Gram matrix method. This method can be easily extended to annulus, and the coefficients of Zernike annular polynomials with no modal cross coupling can be obtained.

To improve the data transmission rate of the conventional point-to-point single input single output (SISO)visible light communication system, a multiple input multiple output (MIMO) visible light communication system is proposed. Considering the complexity of the receiver system, multiple input single output (MISO) visible light com-munication systems have attracted attention. This paper studies the MISO visible light communication system based on pulse amplitude modulation (PAM), and experimentally proves the advantages of this system in specific scenes. In addition, there are non-linear effects for key devices such as LED light sources and power amplifiers in visible light communication systems. Based on 2×1 MISO visible light communication system, this paper reports a novel equal probability coding mapping scheme for high-order PAM signals with two low-order PAM signals superposition in the optical domain. The system verification is performed through a net data-rate of 700 Mb/s transmission experiment through a red chip of RGB-LED, which proves the feasibility and superiority of this scheme in practice.

In order to improve the transmission performance of all-fiber Mach-Zehnder interferometer (MZI), a novel all-fiber MZI interleaver is proposed and discussed in this paper. All-fiber interleaver consists of one 2×2 fiber coupler and one coupler with self-feedback fiber ring resonator. According to its structure, the output expression of the device is deduced by using optical fiber transmission theory and matrix theory, and numerical simulation analysis is per-formed. The results show that the device adopts the phase adjustment effect introduced by the self-feedback optical fiber resonator with reasonable parameters, and its 25 dB cutoff bandwidth is 46.7 GHz which accounts for 93.4% of the 50 GHz frequency interval. The output spectrum is similar to the square wave output. This device requires 2 fiber couplers, which is less than the number of couplers needed for the conventional all-fiber MZI-interleaver. When considering the existence of transmission loss, there is no difference in the amplitude of the two interference optical signals, which reduces the influence of transmission loss on the extinction characteristics of the filter. Compared with the conventional unbalanced MZI type interleaver with an optical fiber resonant ring, the structure is simple and compact, and has a certain anti-deviation ability. It also reduces the difficulty of making the device, which makes it play an important role in the future of dense wavelength division multiplexing systems.

The fiber geometry of communication fibers and medical fibers are always standards to evaluate the quality of optical fibers. The measurement of fiber geometry with gray scale method is one of the commonly used measurement methods. It is also the proposed method in the national standard GB15972.20-2008. In this method, the fiber geometry is obtained by fitting the elliptical curve and fitting the circular curve in two steps, but the center of the two curves may not be coincided. Thus, there is a defect in the measurement principle in the method. The measurement of fiber geometry with gray scale method has a high requirement for cutting effects and lighting conditions. When measurement conditions change, it often leads to the instability of the measured data and brings errors. In this paper, we use the arbitrary elliptical function (non-standard ellipse) which is more suitable for the fiber end face, and only use this function fitting method to get the fiber geometry to fundamentally eliminate the principle defect caused by the inconsistent center fitting between the circle fitting and the ellipse fitting. At the same time, the re-quirement of measurement condition is reduced, because the specific value of image distribution grayscale is not needed when calculating each parameter. Experiments show that this method can effectively improve the stability and consistency of measurement results.

Fiber optic gyroscope (FOG) drift data is often submerged in various noises backgrounds. It is very difficult to compensate for modeling drift signals directly. In order to better eliminate the noise mixed in the FOG temperature drift data, a hybrid EMD-LWT filtering algorithm based on empirical mode decomposition (EMD) and lifting wavelet transform (LWT) threshold denoising was proposed for gyro signals preprocessing. Firstly, the noise signal of fiber optic gyro is decomposed by EMD, and the noise term and the mixed modal term of the intrinsic mode functions (IMF) are judged according to the information entropy. Then the noise term is de-noised by LWT and the mixed modal term is denoised by wavelet transform (WT). A static test was performed on an interferential FOG to verify the effective-ness of the algorithm and compared with WT and LWT. The experimental results show that the proposed EMD-LWT filtering algorithm has better filtering effect. After processing, the root mean square error (RMSE) of the recon-structed signal is reduced by 63%, which effectively removes the noise in the FOG output.

It is an important part for studying lightning to measure lightning current. Consequently, this paper studied an all-fiber optical current transformer for measuring lightning currents. Firstly, the basic principle and structure of the all-fiber optical current transformer were introduced. Then, the performances including the response speed, mea-surement accuracy and measurement range were tested in the laboratory. The results show that the response speed of the sensor is in microsecond. The measurable range is over 1 kA～100 kA. The dynamic range is greater than 40 dB and the measurement error is less than 5%. The measurement waveform of all-fiber optical current transformer coincides with that of standard Pearson current probe. The paper provides a new method for lightning current measurement.

When the line width or line space of thin film transistor (TFT) is close to the resolution of the lithography machine, it is easy to appear the defect of photoresist remain in lithography pattern. In order to improve this problem, based on the position of the best lithography pattern, the optimal compensation amount of lithography plane of the lithography machine is calculated, so lithography plane is improved. Firstly, by the compensation of the lithography plane, the flatness of the plate stage and the focal plane, the value of the plate surface height is calculated in the li-thography region. Then, according to the lithography pattern in the lithography region, the optimum position of the lithography region is found, and take this location as the zero point, the relative height difference between the total lithography region and the optimum position is calculated. Secondly, the fitting plane of the height difference in the lithography region is done, and the compensation is calculated when the fitting plane is the horizontal plane that is perpendicular to the Z axis, which is the optimal compensation of the lithography plane in the lithography region. Finally, the compensation is used to compensate the lithography plane, so that the lithography plane in the litho-graphy region tends to the same optimal lithography plane. The results show that the lithography pattern can be clearly formed in the lithography region after the lithography plane is offset, the defect of the photoresist remain is improved, at the same time, the average value of the develop inspection critical dimension (DICD) is reduced by 1.38% in the target value range, and the uniformity of the DICD is increased by 20%.

In view of the end-to-end communication interruption problem of armored formations in complex battlefield environments, relay-assisted methods are often used to establish cooperative communications links, and the choice of relay is a key issue. In order to improve the communication coordination ability among formations, an optimal relay selection algorithm for armored formations based on wireless ultraviolet (UV) covert communication is proposed on the premise of decode-and-forward protocol, combined with the threshold decision idea. The algorithm combines the advantages of UV NLOS(non-line-of-sight) communication. The optimal relay selection is made for the formations according to the signal-to-noise ratio (SNR) threshold and channel characteristics selection strategy, and the bit error rate (BER) performance is analyzed under Gaussian noise model. The simulation results show that the optimal relay link can be obtained by selecting the appropriate cooperation threshold according to different SNR environments and relay number. Furthermore, adjusting the receiving and transmitting status of the relay, when the cooperative com-munications link changes dynamically, can effectively improve the communication quality of the cooperative relay link.

The fluorescence enhancement effect of CdSe quantum dots (QDs) was measured by using a picosecond pulsed laser with a 532 nm excitation wavelength to induce surface plasmon (SP) on a gold nanograting surface. A layered thin film was prepared on the gold film surface of silicon fund by atomic force microscope (AFM) etching and self-assembly method, respectively. The fluorescence spectrum of CdSe QDs was measured by adjusting the power of picosecond pulsed laser on a micro-Raman measuring platform. The results showed that the structure of the gold nanograting and CdSe QDs could greatly enhance the far-field fluorescence of CdSe QDs, the maximum fluores-cence intensity was up to 7.80 times, and it had been saturated rapidly at the point of reaching the maximum inten-sity. The results of this study could be widely used in fields of the optoelectronic devices, biomedical detection.

A new CNN-based deep neural network, multi-scale one-dimensional convolutional neural network (MS 1-D CNN) was proposed to improve the efficiency and accuracy of vibration event recognition for a phase-sensitive optical time-domain reflectometry (Φ-OTDR) distributed optical fiber vibration sensing system. The raw vibration signals are pre-processed first to remove noise as far as possible. The pre-processing operations include pre-emphasis filtering, normalization and spectral subtraction. The pre-processed signals are used as the inputs of MS 1-D CNN directly. MS 1-D CNN realizes the end-to-end feature extraction of vibration signals and finally recog-nizes the vibration events by using a fully-connected layer (FC layer) and a Softmax layer. In comparison with two-dimensional convolutional neural network (2-D CNN) and one-dimensional convolutional neural network (1-D CNN), the proposed method balances the time and frequency scales better during feature extraction and reduces the pending parameters of the whole neural network. A vibration recognition experiment was designed to classify the three types of the vibration events including damaging, knocking and interference. The recognition results show that MS 1-D CNN achieves similar recognition performance, over 96 percent, at twice processing speed compared to 2-D CNN. Therefore, it is beneficial to improve the real-timing of vibration monitoring while maintaining the recognition performance.

This paper presents an extrinsic Fabry-Perot (F-P) cavity optical fiber temperature sensor, which is based on the frequency-modulated continuous-wave laser interference. The temperature sensing probe is fabricated by a stainless-steel tube with high coefficient of thermal expansion to encapsulate the F-P cavity. Stainless steel tube is used as the F-P cavity and also the temperature sensitive component. The variation of cavity length caused by thermal expansion of F-P cavity is measured by frequency-modulated continuous-wave interferometric measure-ment technique. The experimental results show that the temperature measurement resolution of the fiber tempera-ture sensor reached 0.0002 ℃ and the temperature measurement sensitivity reached 3022 nm/℃. The temperature sensor not only has high sensitivity and resolution, but also has a simple and stable structure and a good application prospect.