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【Objective】With the continuous emergence of information-based bandwidth-consuming services such as 5th Generation Mobile Communication Technology (5G), the Internet of Things, and cloud computing, people’s demand for high-speed information transmission has increased dramatically. However, due to the inherent nonlinear effects, the transmission capacity of single-mode optical fiber has approached the Shannon limit, and it will no longer be able to meet people’s needs for ultra-high-speed and large-capacity transmission. Solving the transmission capacity problem has become a top priority. In order to solve the needs of large-capacity communication systems and long-distance high-speed transmission problems, we have built a two-mode single-channel C-band Few Mode Fiber (FMF) transmission system.【Methods】At the transmitting end, an arbitrary waveform generator is used to convert the digital signal into an electrical signal and drive the In-phase and Quadrature (IQ) modulator to modulate the optical carrier. The modulated signal is transmitted simultaneously using two multiplexing technologies: Mode Division Multiplexing (MDM) and Polarization Division Multiplexing (PDM). In order to achieve long-distance transmission of dual-mode signals of 1 000 km, we construct a dual-circulation loop system. Each time the signal passes through the loop, it will pass through a 50 km FMF. After being transmitted to the target distance, the coupler outputs the signal to the demultiplexing module, and the coherent optical receiver performs homodyne detection on the demultiplexed modulated signal. Finally, the transmitted signal is stored in an oscilloscope for offline Digital Signal Processing (DSP). The signal is sequentially subjected to frequency domain dispersion compensation, downsampling, clock recovery, and least mean square algorithm to restore the original signal.【Results】It was found that within the range of Optical Signal-to-Noise Ratio (OSNR) of each channel in the experiment, the Bit Error Rate (BER) under low Signal to Noise Ratio (SNR) is close to the theoretical channel result. Under high SNR condition, the BER is 1×10-2, which is 2.5 dB away from the theoretical value. We test the BER of LP11a and LP11b modes at Back-To-Back (BTB) and 250, 500, 750 and 1 000 km transmission cases respectively. The BER at all distances are lower than the Low-Density Parity-Check (LDPC) soft decision threshold with 28% redundancy (5.2×10-2 Soft Decision - Forward Error Correction (SD-FEC)). The BER after 1 000 km transmission in the two modes are 1.7×10-2 and 1.8×10-2 respectively, and the total net transmission rate is 400 Gbit/s.【Conclusion】This article demonstrates the transmission of a 32 Gbaud MDM-PDM-16 Quadrature Amplitude Modulation (QAM) C-band signal in a 1 000 km two-mode single-channel FMF system. At the receiving end, the advanced Multiple Input Multiple Output (MIMO)-DSP algorithm is used for channel equalization, and the obtained two-mode BER of 1.7×10-2 and 1.8×10-2 are both lower than the LDPC SD-FEC threshold with 28% redundancy. The result reachs a domestic record of 400 Gbit/s net transmission rate based on FMF transmission, and highlight the potential of FMF in large-capacity long-distance transmission.

【Objective】Single-photon detection and single-photon ranging systems have widespread applications in three-dimensional imaging and long-distance spatial remote sensing. However, device limitations and background noise from the sun light limit the application to only nighttime conditions.【Methods】We have improved traditional laser radar systems by implementing all-fiber optics systems with ultra-narrowband fiber optic filtering, leading to significantly improved system stability. By implementing mechanical motion control, we are able to attain single-photon imaging systems with ultra-wide scanning and ultra-high resolution. The systems can operate in optical environments that are typically challenging, such as daytime or foggy weather. Moreover, the laser radar system is designed based on the 1 550 nm wavelength which has good atmospheric penetration and low transmission loss, enhancing its ability to work in foggy and rainy conditions.【Results】In a foggy condition with a visibility of about 500 m, the system achieves three-dimensional imaging of objects 1.6 km away, which is a distance 3 times longer than the visibility at the time. The distance resolution can be significantly enhanced by optimizing the intensity and distance information of the histogram using the minimized negative logarithmic likelihood function, with the assistance of a high-resolution time/digital converter and the model constructed by the system response function of the laser radar. Compared to the maximum value method with a distance resolution of 0.05 m, this system achieves a distance resolution of 0.006 m via the minimized negative logarithmic likelihood function method. Additionally, the image normalization processing is performed to suppress fluctuations in photon technology and eliminate noise in the image. The 1 550 nm all-fiber laser radar system has strong mechanical stability and can work in adverse weather conditions.【Conclusion】It has significant application value in remote sensing and mapping, ground and vehicle-mounted laser radar, and other fields.

【Objective】To improve the linear fit between the reflected spectral center wavelength and external environmental variables in Fiber Bragg Grating (FBG) sensing system, this paper proposes to use particle swarm optimization of Gaussian process regression model to the field of FBG stress sensing.【Methods】For the reflectance spectral characteristics of the FBG, the paper studies the impact of the linear fit in the spectral fitting of FBG sensing system. The particle swarm algorithm is used to search for the optimal hyperparameters in the Gaussian process regression model in order to enhance the predictive performance of the reflectance spectral wavelength of the center. A FBG stress sensing experimental platform was built, and the FBG was laid on the strength beam. Different weights were applied to one end of the equal strength beam to produce axial strain on the FBG, and the reflectance spectral data were collected by the spectrometer and analyzed by linear fitting with the studied model. The results obtained by the unoptimized Gaussian process regression model, the maximum value method, the Gaussian fitting method, and the center of mass method were used as the control group.【Results】The results show that under the conditions of erbium-doped fiber amplifier output power of 10 dBm, transmission fiber distance of 50 m, and the number of sampling points of the spectrometer of 501, the linear fit between the reflected spectral center wavelength and the mass of the weights is better than that of the control group. The linear fit of the studied model can reach up to 0.951 9, which is improved compared with that of the control group. Under the conditions of 501, 251, 167 and 126 spectral sampling points, the studied model can improve the linear fit of the system to 0.990 0, which is a maximum improvement of 0.258 7 compared with the maximum value method.【Conclusion】The analysis results show that the Gaussian process regression model optimized by the particle swarm is able to effectively improve the linear fit of the FBG stress sensing system.

【Objective】The optical communication system working at the traditional telecommunication band is faced with "capacity crunch" with the rapidly development of optical communication technology. The acceptable loss of 0.2 dB/km (@2 μm) from the hollow-core photonic bandgap fibers as well as the high optical amplification gains (30 dB@2 μm) of thulium-doped fiber amplifiers (CTFA type) provides the potential for the 2 μm wavelength band to alleviate the communication "capacity crunch". As a result, the needs of the 2 μm silicon-based photodetectors is also raised due to its mature and convenient manufacture process. The main solutions of the silicon-based photodetectors include the usage of Ⅲ-Ⅴ compounds with tunable band gap, the introduction of low band gap width materials as absorption regions, the use of new absorption mechanism in optical absorbed material at the 2 μm wavelength band and so on. The Ge material has a high Two Photon Absorption (TPA) coefficient (1 225 GW/cm@2 μm). And the Ge-on-Silicon-On-Insulator (SOI) photodetector is an excellent method to realize 2 μm optical signal detection, which is compatible with the standard silicon photonics device manufacturing process that has the advantages of low production difficulty and cost. The purpose of this paper is to verify the feasibility of the Ge-on-SOI photodetector to achieve 2 μm wavelength band photoelectric detection by using the special optical absorption mechanism of TPA.【Methods】In this paper, the photoelectric detection at the 2 μm wavelength band based on the physical absorption mechanism of current generated from high TPA of Ge material is realized. The quantification of the photocurrent generated by Ge material through TPA effect is analyzed and discussed in this paper. In the experimental test, we first apply a high power 2 μm wavelength band input light source magnified by thulium-doped fiber amplifiers to the input port (grating coupler) of the commercial waveguide-type Ge-on-SOI photodetector in the on-chip active silicon photonics device test system. Then we adjust the alignment of the optical fiber with the grating coupler and the input light polarization to reduce the optical transmission loss from the input optical fiber to the Ge absorption region. Finally, the TPA photocurrent of the on-chip photodetector is obtained by a probe.【Results】A net photogenerated current up to 651 nA and an estimated value of responsivity greater than 10 mA/W is obtained experimentally under a 2 μm wavelength optical input power of 21.9 dBm.【Conclusion】The work of this paper verifies the scientific feasibility of 2 μm waveband photodetector through the TPA effect of Ge material, and provides experimentally support for the design of the 2 μm wavelength band Ge-on-SOI photodetector based on TPA.

【Objective】In order to solve the problem of cross sensitivity of temperature and strain in Fiber Bragg Grating (FBG) sensing, the response characteristics of temperature and strain in each mode of Few Mode Fiber (FMF)-FBG were studied in this paper. A four-mode FBG temperature and strain dual parameter sensor was also proposed.【Methods】The basic mode and a few higher modes can be transmitted simultaneously in the low-mode fiber, taking into account the advantages of low mode dispersion of Single Mode Fiber (SMF) and low nonlinearity of multi-mode fiber, which can be used for sensing multiple physical quantities at the same time. By analyzing the different optical power sensitivity of the LP01 mode in the FMF-FBG at different temperatures, and considering the good linearity of wavelength, temperature and strain under this mode. Thus, the temperature and strain dual parameter sensing of FMF-FBG is realized.【Results】The results show that the sensor can better solve the problem of cross sensitivity of temperature and strain.【Conclusion】Compared with SMF-FBG, the FMF-FBG has several reflection peaks of different modes at the same time, which can not only solve the cross-sensitivity problem of temperature and strain, but also greatly improve the accuracy and stability of sensing, which may have a good application prospect in the field of new type of sensing.

【Objective】The light source of fiber grating sensing system provides energy for the system. The stable and continuous light source is crucial for the application of the whole demodulation system. When the Modulated Grating Y-branch (MG-Y) laser is used as the light source of the fiber grating demodulation system, it is necessary to solve the problem that it is difficult for the MG-Y laser to quickly obtain the stable and continuous tuning within the required specific wavelength range.【Methods】In order to obtain the stable and continuous wavelengths quickly for MG-Y lasers, the K-Means (KMeans) clustering model is proposed and applied to obtain high-quality current-wavelength Look Up Table (LUT) for MG-Y lasers.【Results】By combining the tuning characteristics of the MG-Y laser with the KMeans clustering model method, the centroid of the optimal tuning parameter curve in the phase tuning region of the LUT can be quickly obtained with time of about 18.26 s. Then, according to the tuning characteristics of the left, right and phase of the MG-Y laser itself, the fine tuning of the MG-Y laser wavelength can be achieved by uniform interpolation method. The LUT with the full tuning range is obtained from the KMeans clustering model, and the target LUT is selected at a certain interval. According to the output wavelength issued by the laser according to the target LUT, the mean value of the measured wavelength and the absolute value of the error of the target wavelength is 0.18 pm. The standard deviation of the absolute value of the error is 0.52 pm. Therefore, the MG-Y laser can be used as a stable light source for the fiber grating sensing system.【Conclusion】It is verified by experiments that the traditional manual search for each phase tuning region needs at least 30 min to find the centroid point. The same operation can be completed by KMeans clustering model method, which can greatly shorten the time to find the centroid point. Based on this method, the stable wavelength of quasi-continuous tuning can be achieved by controlling the MG-Y laser.

【Objective】In the production test process of 50 Gbit/s Small Form Pluggable (SFP) 56 optical module, the number of instruments and equipment to be matched for the test is large. Therefore, the test instruments are used in isolation, and the test process is complex. These issues make the optical module test longer, and the test efficiency is relatively low. It brings a lot of inconvenience to the test personnel, and can not guarantee the consistency of the test products. The purpose of this paper is to enhance debugging and testing efficiency while alleviating testers' workload.【Methods】Python language and its robust third-party libraries, including the VISA and pyserial libraries, are utilized to develop an automatic testing system for SFP56 optical modules compatible with the Windows operating system.【Results】The system can debug and test the optical module automatically. The test instruments can be used in parallel, reducing the waste of time and resources. According to the test requirements, the optical module can also be tested step by step, which greatly improves the efficiency of the debugging and testing of the optical module in the production line. It can also reduce the requirements of the tester. The verification shows that compared with the traditional optical module test, the test time of each optical module is saved by about 70 s, which greatly improves the test efficiency of the optical module. In the optical module test, the result deviation caused by human operation is avoided, and the product consistency can be guaranteed.【Conclusion】In comparison to Labview-based automatic optical module testing systems, which are currently prevalent in the market, the system designed in this study is more scalable and convenient for upgrades and maintenance. Moreover, it can be expanded to support optical module testing at speeds of 100, 200, 400, and 800 Gbit/s, thus laying a technical foundation for future high-speed optical module testing.

【Objective】E/W band millimeter-wave frequency covers 60~110 GHz, with abundant frequency band resources and potential for high-capacity transmission. Compared with lasers, E/W band millimeter-wave beam is wider, with advantages of directionality, anti-interference and ease of alignment, making it a promising frequency band for long-distance wireless communication at sea. However, the characteristics of near-sea surface channels such as atmospheric absorption and multipath at the sea surface limit the transmission distance of E/W-band millimeter waves, resulting in bottlenecks in E/W-band millimeter wave transmission near-sea surface. This paper focuses on the direction of long-distance millimeter-wave wireless transmission at sea, using microwave photonics technology to propose an ultra-wideband millimeter-wave modulation and demodulation system architecture to improve the millimeter-wave frequency conversion and modulation performance. We then study the optimal high-order modulation format in near-sea surface long-distance transmission systems to achieve high-capacity long-distance transmission.【Methods】The power amplifier in long-distance communication systems can introduce nonlinear distortion to the signal. It analyzes the factors affecting the performance of high-order modulation formats such as Amplitude Phase Shift Keying (APSK) and Quadrature Amplitude Modulation (QAM) due to the nonlinear characteristics of solid-state power amplifiers. The optimal distribution, Euclidean distance and inner and outer radius ratio of 16APSK signals have been studied. By the equivalent power experiments, the nonlinear resistance of 16QAM and 16APSK signals are compared and analyzed.【Results】The millimeter-wave long-distance transmission experiment is carried out for performance investigation. It proves that the APSK modulation format is more suitable for long-distance transmission system than QAM format.【Conclusion】Based on the 16APSK modulation format, the performance of 16 Gbit/s, equivalent 34 km long-distance transmission are achieved in the experiment, providing high-value technical means for long-distance high-capacity transmission at sea.

【Objective】In order to solve the problem of the limited bandwidth of polarization insensitive optical power splitter, an ultra-broadband polarization insensitive optical power splitter based on Silicon Nitride (Si3N4) waveguide is proposed.【Methods】The ultra-broadband polarization insensitive optical power splitter is designed based on adiabatic coupling Si3N4 waveguide.Optical bandwidth of 300 nm (from 1 400 ~ 1 700 nm) is demonstrated for both Transverse Electric (TE) and Transverse Magnetic (TM) modes.【Results】Over the entire optical bandwidth, the losses for TE and TM mode are less than 0.10 and 0.15 dB, respectively.The footprint of the proposed ultra-broadband polarization insensitive optical power splitter is only 60.00 μm×2.75 μm, which means that the optical power splitter can be used for large-scale integration.Furthermore, the relationship between the performance and the structure parameters of the proposed optical power splitter is studied.【Conclusions】The results show that the performance of the optical power splitter maintains almost unchanged by varying the structure parameters with ±50 nm.In other words, the optical power splitter possesses large fabrication tolerance which can be easily fabricated.

【Objective】In this paper, machine learning method is applied to 30 Tbit/s (60 × 500 Gbit/s) Nyquist Dual Polarization-16 Quadrature Amplitude Modulation (DP-16QAM) system after 6 300 km transmission in G. 654E optical fiber. Nonlinear channel equalization is used to reduce the transmission Bit Error Rate (BER).【Methods】Referring to the "receptive field" mechanism of convolution neural network, the size of "convolution core" is designed, and the data set is constructed according to the divided sampling data. The artificial neural network is constructed by optimizing the parameters. The one-to-one data corresponding to the transmission and reception of different wavelengths, different optical signal-to-noise ratios, and different fiber input powers in the C-band are collected. Refer to the classic full-connection neural network structure, the neural network is constructed according to the data structure of the data set. The network fitting is carried out for the real part and the imaginary part respectively. After training stage, the test data is sent into the network, and the performances are compared with the traditional methods.【Results】Two kinds of neural networks are used to fit the transmission BER under 60 different wavelength transmission conditions of C band frequency from 191.562 5 to 195.987 5 THz. Compared with Maximum Likelihood Sequence Estimation (MLSE), Network 1 has an average reduction of 23% in BER, and Network 2 has an average reduction of 41% in BER. A frequency of 193.812 5 THz is then selected for the calculation of the fiber input power ranging from 14 to 19 dBm. The average improvement in network 1 and network 2 are 32% and 52%, respectively. Under different optical signal-to-noise ratios, Network 1 has an average improvement of 30%, and Network 2 has an average improvement of 57%.【Conclusion】The two neural networks have excellent performance in nonlinear equalization of coherent transmission systems. At the same time, the number of network layers and nodes will jointly affect the fitting results. Increasing the number of layers and nodes can obtain better fitting results, but the corresponding parameters, training time and the required space will also increase. Therefore, in the application, the actual situation should be considered to choose between the fitting performances and the model attributes.

【Objective】The significance of wireless network equipment troubleshooting can be used to solve the network connection problems, improving user experience, and maintaining network stability and reliability. However, the accuracy of existing methods needs to be further improved.【Methods】To address this problem, this paper quotes the attention mechanism in the Convolutional Neural Networks(CNN)- Gated Recurrent Unit (GRU) network structure and proposes a wireless network equipment fault diagnosis method based on the CNN-GRU-Attention network structure.【Results】Compared with other methods in the simulation experiment, the method in this paper improved the accuracy of the model from 91% to 98%.【Conclusion】Through the research of this article, the quality and efficiency of wireless network equipment operation have been improved. The network capacity, functionality and reliability have also been improved, and people's growing communication needs for wireless networks have been met.

【Objective】There is a problem that traditional unrepeatered transmission system need to use disturbed Raman amplifier and remote optical pump amplifier, while both of these two amplifiers need to use high power pump laser which will increase the complexity of fiber link in unrepeatered transmission system. In this paper, we propose a new structure of unrepeatered transmission system using Erbium Doped Optical Fiber Amplifier (EDFA) to replace the forward disturbed Raman amplifier.【Methods】We analyze and compare the performance of the proposed unrepeatered transmission system, and realize a real-time unrepeatered transmission experiment with the proposed structure.【Results】The results show that the gain effect of forward Raman pump in traditional unrepeatered communication system can be achieved by using high power amplifier to increase the signal launch power, and the new structure of unrepeatered transmission system is more suitable to achieve higher bitrate with the help of Wavelength Division Multiplexing (WDM) technology. We confirm the unrepeatered transmission system can achieve 500 km span distance at 10 Gbit/s bit rate in single channel communication transmission, and 500 km span distance at 4×10 Gbit/s bit rate in the WDM technology.【Conclusion】The proposed unrepeatered transmission system can simplify the traditional unrepeatered transmission system, and increase the bit rate by using multi-channel WDM system with EDFA. It has important practical significance to simplify the structure and improve the bit rate in future unrepeatered transmission system.

【Objective】Light Emitting Diode (LED) is an important nonlinear optical signal generating device in Visible Light Communication (VLC) systems. The static nonlinearity of LED and the dynamic nonlinear memory effect caused by frequency response can lead to signal distortion and degrade the system performance.【Methods】The nonlinearity of LED can usually be compensated by estimating a pre-distortion model, and the wireless VLC is usually intensity modulated/directly detected.【Results】Therefore, the LED nonlinearity modeling is investigated, and an adaptive pre-distortion device based on Amplitude Factorization Polynomial (AFP) is proposed to compensate LED nonlinearity in this paper. Simulation results show that the proposed scheme exhibits good Bit Error Rate (BER), Amplitude Modulation/Amplitude Modulation (AM/AM) correction and constellation diagram performance with higher modeling accuracy.【Conclusion】The normalized mean square error performance improvement of more than 15 dB compared with the traditional memory polynomial is achieved.

【Objective】The symbol decomposition technique aims to decompose Optical Orthogonal Frequency Division Multiplexing (O-OFDM) symbols into multiple symbols with a small Peak to Average Power Ratio (PAPR) to mitigate the non-linear effects of Light Emitting Diodes (LEDs). However, O-OFDM generates more decomposed symbols with a higher PAPR, thereby reducing the information rate and degrading the Bit Error Rate (BER) performance.【Methods】The proposed design of Precoding O-OFDM Adaptive Symbol Decomposition with Serial Transmission (PCO-OFDM-ASDST) system uses precoding scheme to reduce the PAPR of O-OFDM symbols. The proposed method can reduce the average number of symbol decompositions for adaptive symbol decomposition. The theoretical Signal-to-Noise Ratio (SNR) expressions are derived for multipath channels, and the performance of PAPR, BER, and information rate is analyzed using Monte Carlo BER simulations.【Results】The results demonstrate that under 4 Quadrature Amplitude Modulation (QAM) modulation in Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) systems, the symbol power required for PCO-OFDM-ASDST is 7 dB less than that of Adaptive Symbol Decomposition with Serial Transmission (ASDST) when the BER is 10-4. Moreover, under 64QAM, the information rate can be increased by 10 Mbit/s when the symbol power is 20 dBm.【Conclusion】The results indicate that the PCO-OFDM-ASDST outperforms ASDST systems in terms of BER and information transmission rate.

【Objective】The use of random mapping and traditional constellations in Optical-Orthogonal Frequency Division Multiplexing (O-OFDM) - Index Modulation (IM) system cannot reach the optimal Bit Error Rate (BER) performance. Therefore, a step-by-step optimal signal mapping method is proposed based on the optimal selection of active sub-carriers and the optimal rotation of constellation to improve the BER performance of O-OFDM-IM system.【Methods】At the transmitter side, the method firstly selects the optimal combination of active subcarriers based on the channel state information and the channel norm maximization criterion. Then considering ∂=0.5° as the step size, an exhaustive search algorithm is used to obtain the optimal constellation by using the channel state information. Next, the optimal constellation graph obtained by rotation is loaded on the active sub-carrier for signal transmission. At last, the Maximum Likelihood (ML) detection algorithm is used to recover the original signal at the receiver to minimize the system error probability.【Results】The results show that at the condition of BER=10-4 and strong turbulence, the Signal to Noise Ratio (SNR) is improved by about 1.45 dB when the modulation order is 16 in (4, 2) system. In addition, with the increase of turbulence intensity, the improvement of BER performance is more obvious. For example, when the BER=10-4 the SNR of the (4, 2) system at 8 Quadrature Amplitude Modulation (QAM) is improved by about 1.35 dB in strong turbulence and 1.2 dB in weak turbulence.【Conclusion】Based on the known channel state information, a step-by-step optimal signal mapping method for O-OFDM-IM is proposed in this paper, which can effectively improve the BER performance of the system in strong turbulence channels.

【Objective】The baseline drift of the Fiber Bragg Grating (FBG) spectral signal is usually one of the main problems, caused by the complex external environment. A spectral baseline correction method based on the improved Long Short Term Memory (LSTM) model is proposed in this paper.【Methods】Compared with LSTM model, the improved LSTM model extracts feature information of FBG spectral signal by the Convolutional Neural Network (CNN). The improved LSTM model is composed of CNN, full connection, and LSTM network. In this paper, the improved LSTM model is trained by artificial datasets and measured datasets. The artificial datasets are made up of feature noise, baseline, and FBG spectroscopy. Five methods including wavelet soft threshold method, penalty least square method, Recurrent Neural Network (RNN), LSTM, and the improved LSTM model are used as baseline correction. Identification signal probability and Root Mean Square Error (RMSE) are used to evaluate correction results by the five methods.【Results】The artificial datasets of FBG signal are corrected by the improved LSTM model, and the identification signal probability is increased by 60.8%. The improved LSTM model with training by artificial datasets and measured datasets shows better correction results, compared with training by measured datasets. The mean of the RMSE for FBG spectrum decreases by 10.95%. The standard deviation of RMSE decreases by 4%. The measured datasets of FBG signal are corrected by the improved LSTM model, and the identification signal probability is increased by 50.5%. Compared with wavelet soft threshold method, penalty least square method, RNN and LSTM, the improved LSTM model shows best correction results. The mean values of RMSE and the standard deviation of RMSE are 0.012 2 and 0.002 4, respectively. The RMSE value of the demodulated central wavelength is 0.036 pm. And the baseline correction process takes only 9.68 ms.【Conclusion】The improved LSTM model is an effective method to achieve baseline correction, and has wide range of application prospects in complex external environment.

【Objective】In long-distance optical communication systems, compensating fiber nonlinear impairment through traditional Digital Signal Processing (DSP) is difficult due to intractable interactions between Kerr nonlinearity, chromatic dispersion and amplified spontaneous emission noise. Machine learning algorithm can be used to further process signals on the basis of traditional DSP to mitigate fiber nonlinear impairment and improve long-distance transmission performance.【Methods】In this paper, the traditional Digital Back Propagation (DBP) algorithm is combined with Deep Neural Network (DNN), where the linear step size and nonlinear step size in DBP are taken as one neuron. It means that the linear step size is taken as the weight matrix of DNN, the nonlinear step size is taken as the activation function, and DSP is taken as the static layer of DNN. A DNN-based Learned Digital Back Propagation (LDBP) algorithm is proposed.【Results】In order to verify the feasibility of the proposed LDBP algorithm, the simulation was carried out in a single-channel polarization division multiplexing 16-ary Quadrature Amplitude Modulation (QAM) optical transmission system. The numerical simulation results demonstrate that the 1-step-per-span LDBP algorithm improves the optimal launched power from -2 dBm to 1 dBm in compared to linear equalization. Meanwhile, compared with DBP with the same computational complexity, the proposed algorithm improves Signal-to-Noise Ratio (SNR) by 0.82 dB at the transmission distance of 1 200 km. In addition, compared with DBP with the same computational complexity and linear equalization, the SNR of the transmission system corresponding to LDBP method decreases more slowly with the increase of transmission distance, and the algorithm can work without knowing the link parameters, showing the characteristic of universality and robustness.【Conclusion】The proposed LDBP algorithm is more suitable for practical long-distance coherent optical communication system than the traditional DBP algorithm.

【Objective】Aiming at the limited transmission distance of ultra-long distance optical transmission system using remote pump technology, this paper proposes a single span repeaterless transmission system with mixed transmission of 100 and 200 Gbit/s service. The experiment tests the maximum span loss of the system by adjusting the input power of the system and the position of the remote pump gain unit in the system without considering the influence of other factors such as dispersion.【Methods】The key amplification technologies in the experiment mainly include remote pump amplification technology, Erbium-doped optical fiber amplification technology and Raman amplification technology. In the transmission, Erbium-doped optical fiber amplifier, Raman amplifier and remote pump gain unit are used to carry out non-relay amplification of optical signals in the system, and the relay transmission distance is further improved by adjusting the position of remote pump gain unit. The remote pump bypass access method which can improve the amplification gain of remote pump is used in the experiment.【Results】Three different modules were used in the experiment, with a total of 9 service waves. The modulation formats of 200 Gbit/s Polarization Multiplexed - Quadrature Phase Shift Keying (PM-QPSK), 100 Gbit/s PM-QPSK and 200 Gbit/s Polarization Multiplexed -16 Quadrature Amplitude Modulation (PM-16QAM) were used respectively. The transmission experiments were constructed by G. 654b ultra-low loss optical fiber with a loss of 0.17 dB/km. Finally, the single-span ultra-long distance transmission with a total capacity of 1.5 Tbit/s and a cross-segment loss of 75 dB is realized.【Conclusion】The results show that the transmission distance of the system can be improved by setting the optimal fiber input power and adjusting the position of the gain unit of the remote pump. The experimental results provide reference value for the construction of the ultra-long distance optical transmission system based on the remote pump technology, and provide reference data for the development of the repeaterless transmission based on the remote pump technology.

【Objective】In order to solve the problem that it is difficult to make the temperature sensor of the Photonic Crystal Fiber (PCF) with Surface Plasma Resonance (SPR), a D-structure PCF temperature sensor is proposed. The micro-structure and arrangement of the air hole are also designed. The method of coating the polishing surface of the optical fiber with gold layer is used to stimulate the SPR of the optical fiber.【Methods】Ethanol is used as a temperature-sensitive material, and the temperature-sensitive effect is used as the temperature sensing mechanism to achieve the effect of temperature sensing. The finite element analysis method is used to simulate the thickness of the gold layer and the size of the elliptical air hole of the fiber respectively. The coupling characteristics between the core mode and the surface plasma mode are analyzed under different conditions, and the structure of the sensor is optimized.【Results】The temperature characteristics of the sensor are simulated. In the range of -80~80 ℃, the sensitivity of the sensor is 3.4 nm /℃, and the linearity is better than 0.969 63.【Conclusion】The temperature sensor designed in this paper has a wide temperature detection range, satisfactory sensitivity, and linearity, which can be used for real-time temperature monitoring in industrial, agricultural, and medical fields.

In recent years, high quality factor echo wall mode optical microcavities have developed rapidly and become a hot research topic in the fields of optics and physics. Optical microcavity is a kind of micro optical element. Due to its small size and high-quality factor, it can enhance the interaction between light and matter, enabling long-time light stays. Echo wall mode resonators are one of the typical representatives of optical microcavities, with advantages of small size, high sensitivity, and long life. Currently, applications based on echo wall mode resonators are mainly concentrated in various fields such as sensors, lasers, filters, and so on. However, current research on echo wall mode resonators has not yet achieved large-scale production, and is only in the laboratory research stage. Industrial production still has shortcomings such as high cost and manufacturing process difficulties. This article focuses on the research progress of echo wall mode resonators, expounds the impact of echo wall materials on Q values, and discusses the applications of echo wall mode resonators in the fields of sensors, lasers, and filters in recent years. It also proposes the challenges and further research directions of echo wall mode resonators in the future, which may realize all-optical networks. For further research directions, we believe that it is necessary to reduce costs, shorten time, and improve the accuracy and efficiency of the preparation process. It is also necessary to solve the coupling problem between the microcavity and the optical device, improving the coupling efficiency and the anti-interference ability. It should also address the sensitivity of the cavity to the environment to ensure that the microcavity has good stability when preparing devices such as filters.

Fiber Bragg Grating (FBG) pressure sensor has the advantages of underwater passive, corrosion resistance, light weight, low cost and anti-electromagnetic interference, which has been widely used. This paper first briefly introduces the basic principle of FBG pressure sensing. It then summarizes the development status of FBG writing technology, pressure sensing and sensitizing technology, and temperature compensation technology. Next, it summarizes the application progress of FBG pressure sensor in the fields of ocean depth, lake level measurement, oil and gas pipeline pressure measurement, and rock and soil pressure monitoring in recent years. Finally, the FBG pressure sensing technology is prospected.

【Objective】Undersea optical cable plays a leading role in international communication. In the planning of undersea optical cable communication system, several groups of possible schemes are often determined according to experience. The scheme with relatively better transmission performance and investment cost is then selected. However, with the development of communication equipment and communication technology, the number of optional modulation formats and optical fibers keeps are increasing. The number of alternative schemes is too large to quickly determine the optimal scheme. Therefore, it is necessary to establish a cost optimization model of undersea optical cable communication system to solve the cost optimal scheme.【Methods】Aiming at the problem of system planning and configuration in the undersea optical cable communication system, a cost optimization model considering the parameters of transmission performance, transmission capacity and supply voltage is established by taking the span length, optical fiber type, number of optical fiber pairs, repeater output power, modulation format and number of practical channels as the variables. The cascaded-lexicographic method is used to solve the cost optimization model.【Results】The results show that the difference between the planning results of the proposed optimization algorithm and full traversal algorithm are no more than 0.34%. However, the number of operations of the optimization algorithm proposed in this paper is far less than that of the full traversal algorithm, with only 1/100 of that of the full traversal algorithm. Secondly, the number of operations of the cascade genelexicography method is less affected by the range of variables than that of the total traversal method. Finally, by comparing the optimal cost of the undersea cable communication system under different span length, it is found that the planning results have no regularity.【Conclusion】The variables always influence each other. The optimal cost design of the system cannot be obtained according to experience, so it needs to establish a model. The algorithm used in this paper is not only accurate, but also uses fewer operation times.

【Objective】With the development of the space-ground integrated information network, the Low Earth Orbit (LEO) satellite communication system is ushering in a development boom. The Paired Carrier Multiple Access (PCMA) technology is gradually developing to the low-orbit satellite communication due to its advantages of saving bandwidth resources. However, traditional PCMA technology is mostly used in high-orbit satellites, and cannot adapt to the highly dynamic fading channel character-istics of low-orbit satellite channels, which greatly degrades the bit error performance of the PCMA receiver. The bottleneck lies in the channel estimation and equalization technologies for overlapping signals.【Methods】Aiming at the channel characteristics of LEO satellites, this paper proposes a channel estimation scheme that combines training sequence estimation and Autoregressive (AR) model prediction. Based on the idea of superimposed training sequence channel estimation, an iterative method suitable for PCMA mixed signal channel estimation is introduced to improve the accuracy of training sequence channel estimation through iteration. The AR model is used to predict the Channel State Information (CSI) of the data sequence in real time. The use of AR model can also reduce the frequency of channel estimation in training sequences, so as to adapt to the dynamics of LEO satellite channels.【Results】The simulation results show that the idea of superimposed training sequence channel estimation can be applied to the PCMA signals, and accurate channel estimation can be obtained after iterations. The method proposed in this paper can effectively improve the accuracy of channel estimation. After signal separation and demodulation, the bit error rate can reach the order of 10-3when the signal-to-noise ratio is greater than 9 dB.【Conclusion】A channel estimation method for PCMA signal is proposed in this paper. The simulation results show that the bit error rate loss is within an acceptable range, which can support the application of PCMA technology in low-orbit satellite communication. The proposed algorithm has the advantages of simple structure, low complexity, and high practical value.

【Objective】With the continuous development of satellite technology, the application of satellites to low coverage areas of ground information networks for personnel search and rescue is becoming increasingly popular. As an effective means of indicating the location of personnel and facilities, satellite search and rescue positioning technology is widely used in maritime, aviation, and personal distress rescue operations. Therefore, in the continuous development and research of global satellite search and res-cue systems, achieving high-precision and rapid positioning of search and rescue sources is the main goal.【Methods】In view of the sudden characteristics of satellite search and rescue signals, dual-satellite Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) positioning are adopted as the satellite search and rescue positioning methods. The estimation of the required TDOA and FDOA parameters is the key to improve the positioning accuracy. In order to improve the parameter estimation performance and positioning accuracy of dual-satellite TDOA and FDOA positioning technology, this paper proposes a search and rescue positioning technology scheme based on time-frequency difference estimation of windowed Cross Ambiguity Function (CAF). The method of filtering redundant noise by adding windows in time domain is introduced, and the accuracy of time-frequency difference estimation is improved by adding windows in time domain and CAF. The estimated value is substituted into dual-satellite TDOA and FDOA positioning equations to calculate the location of the search and rescue signal source. It means that the purpose of improving the positioning accuracy is to efficiently and accurately find the search/rescue source by improving the estimation accuracy of TDOA/FDOA parameters.【Results】The simulation results show that the method of estimating the TDOA/FDOA parameters of CAF with windows can be applied to search and rescue positioning, and the accurate time-frequency difference estimation value can be obtained through this method. The method proposed in this paper can effectively improve the accuracy of time-frequency difference parameter estimation, and add Fourier transform to reduce the time of parameter estimation, thus optimizing the positioning performance. When the TDOA error is controlled within 4 μs and the FDOA error is controlled within 0.2 Hz, the positioning accuracy can reach the kilometers.【Conclusion】The time-domain windowed time-frequency difference parameter estimation scheme proposed in this paper has improved the positioning performance after being incorporated into the satellite search and rescue positioning technology, which can support the application of the satellite search and rescue positioning technology in the satellite search and rescue system. The algorithm has the advantages of simple structure, low complexity and practical feasibility.

【Objective】The non-linear characteristics of Light Emitting Diodes (LEDs) contribute to the degradation of Bit Error Rate (BER) performance in Visible Light Communication (VLC) systems, particularly in Optical Orthogonal Frequency Division Multiplexing (O-OFDM) systems with high Peak-to-Average Power Ratio (PAPR). A single-stage equalizer based on the Volterra series can handle the high-order non-linear distortions of LEDs with low latency. However, solving the traditional Volterra series necessitates multiple integration operations, resulting in the high implementation complexity of the Volterra-based equalizer. Additionally, the single-stage equalizer accumulates errors with limited performance improvements.【Methods】Firstly, to address the issue of high computational complexity in the traditional calculations of the Volterra series, a proposition is made to retain only the high-order power series terms of the various nonlinear terms and kernel coefficients within the Volterra series. This approach, known as the Memory Polynomial-based Volterra Series (MPVS), not only reduces the computational complexity compared to the traditional Volterra series but also enhances the accuracy of nonlinear system modeling by considering all input signals at the current moment. Subsequently, the design of channel equalizer considers the Memory Polynomial-based Volterra (MPV) equalizer and the Memory Polynomial-based Volterra Decision Feedback Equalizer (MPV-DFE). For a single-stage MPV-DFE, if an error occurs in the decision part leading to an incorrect symbol decoding, this error tends to manifest as a consecutive series of errors, thereby impacting the entire symbol sequence. To mitigate this, a proposal is made to cascade the two non-linear equalizers, MPV and MPV-DFE, forming a hybrid equalizer called MPV+MPV-DFE. The MPV equalizer performs a primary equalization on the LED's nonlinear distortion signal, effectively suppressing a portion of the non-linear distortions and thereby reducing symbol decoding errors in the MPV-DFE. Subsequently, a secondary equalization is carried out by the MPV-DFE, leading to improved suppression of residual nonlinear distortions.【Results】Finally, the effectiveness of the system design was validated using Monte Carlo simulation to analyze the BER. The results demonstrate that compared to the single-stage MPV equalizer and the linear-cascade nonlinear hybrid equalizer (LMS+MPV-DFE), the proposed hybrid equalizer achieves approximately 7 dB and 2 dB Signal-to-Noise Ratio (SNR) gains, respectively, in a 4 Quadrature Amplitude Modulation (QAM) -modulated Asymmetrically Clipped Optical OFDM (ACO-OFDM) system at a BER of 10-4.【Conclusion】In conclusion, the implementation of the MPV equalizer is straightforward, and the cascaded design of the two-stage nonlinear equalizers as a hybrid equalizer enables better mitigation of the LED’s nonlinearity.

In recent years, many new modulation and multiplexing technologies and dynamic network concepts have been proposed to adapt to the ever-increasing network bandwidth and quality requirements. Network control platform has a systematic and intelli-gent development trend, which requires network managers to constantly monitor the parameters of the network and optimize the network state. However, it is not feasible to arrange additional monitoring equipment in a large range to obtain parameter informa-tion from the perspective of cost control. It is better to use known data and special algorithms to monitor and optimize network per-formance. Machine learning methods are increasingly adopted by the academic community because they are accurate and efficient enough to accomplish these tasks. This paper first reviews the different application scenarios of machine learning algorithms in op-tical network monitoring and optimization tasks. Then it reviews the research achievements in this field, and puts forward the ex-isting problems of machine learning-based optical network monitoring and optimization methods as well as the possible direction of future research. The optical performance monitoring based on machine learning includes failure identification, quality of transmis-sion estimation and channel power prediction. The network configuration optimization method based on machine learning includes reinforcement learning to optimize channel power. For future research direction, we believe that it is possible for researchers to use real data from network operators, newly collected data to dynamically train the model, and transfer learning and data enhancement techniques to ensure the robustness and generalization ability of the algorithm.

The single-satellite multi-beam interference source localization method requires more than three co-frequency beams to receive the interference source signal to achieve positioning. Due to the limited number of co-frequency beams and the randomness of the location of the interference source, it is usually that the co-frequency beams can receive the interference source signal less than three, or low receiving gain, which may affect the positioning accuracy.【Objective】In order to solve the problem of positioning with only two available beams and further improve the positioning accuracy of interference sources, a dual-satellite joint positioning model based on multi-beam antenna and Time Difference of Arrival (TDOA) technology is proposed through adjacent stars and main stars.【Methods】In this paper, the feasibility of the model is proved by establishing the dual-satellite joint positioning model and the positioning equations in parallel. At the same time, based on Geometric Dilution of Precision (GDOP), the positioning error of the positioning model is analyzed from four aspects: receiving gain error, beam pointing error, arrival time difference error and position prediction error.【Results】The simulation results show that the positioning accuracy of the dual-satellite joint positioning method based on multi-beam antenna and TDOA technology is obviously better than the traditional single-satellite multi-beam positioning method.【Conclusion】The dual-satellite joint positioning method based on multi-beam antenna and TDOA technology makes use of the advantage that TDOA has less influence on positioning accuracy. Therefore, it replaces part of the beam to participate in satellite positioning, which not only reduces the demand for the number of positioning beams, but also reduces the error of measurement gain and the error of beam pointing with improved positioning accuracy and the reliability. The simulation results indicate that the proposed method is a better positioning method than single-satellite multi-beam positioning.

【Objective】Aiming at the problems of low spectral efficiency and limited system throughput in Optical Quadrature Spatial Modulation (OQSM), a Signed Optical Quadrature Spatial Modulation (SOQSM) scheme is proposed in Free Space Optical Communication (FSOC) in this paper. In addition, in view of the fact that the channel used in the performance analysis of OQSM is not suitable for all turbulence, this paper also adopts the Málaga channel, which is suitable for all turbulence intensities to analyze the bit error performance of the system.【Methods】First, the scheme divides the input binary bit stream into five parts at the sending end. The first part is used for constellation symbol mapping, and the last four parts are used for laser mapping. Then, the constellation symbol mapping is used to transmit the real and imaginary parts of the constellation symbol and its inverse symbol. The laser mapping is divided into two parts, the in-phase phase and the quadrature phase, which are used to activate the laser sequence mapping. Finally, after transmitting through the channel, the signal received and processed at the receiving end.【Results】Compared with OQSM, SOQSM carries an additional2log2Nt bits of information in the space domain within a transmission period. The upper bound of the average bit error rate is then calculated in the symbol domain and the space domain respectively. Finally, the upper bound of the average bit error rate of the SOQSM scheme is obtained, and the method of calculating the upper bound of the average bit error rate has good convergence. This solution greatly improves the spectral efficiency and transmission rate of the system, and has good bit error rate performance.【Conclusion】The Monte Carlo simulation results show that compared with Optical Spatial Modulation (OSM) and OQSM, the bit error performance of the SOQSM scheme is better when the spectral efficiency is the same. The bit error rate can reach 10-6 when the signal-to-noise ratio is 16dB. When the modulation order is the same, the bit error performance of SOQSM is better, especially when the signal-to-noise ratio is high. It is also shown that the simulation and theory fit well. In the Málaga channel, the bit error rate performance of the weak turbulence is better. In addition, different turbulence intensities have little influence on the trend of the bit error rate performance of the SOQSM scheme. However, with the increase of the signal-to-noise ratio, the influence will gradually increase. Therefore, SOQSM has better bit error rate performance than OQSM and OSM.

【Objective】In the Low Earth Orbit (LEO) satellite Internet of Things (IoT) scenario, the time delay and power consumption requirements of Narrowband (NB) -IoT terminal in wide coverage area vary due to different business scenarios. However, the ground NB-IoT terminal with a single business scenario adopts a fixed working state timer parameter configuration method, which cannot meet the needs of time delay and power consumption for multi-scenario terminals in large geographical areas of LEO satellite IoT.【Methods】In response to the wide coverage characteristics of LEO satellite IoT, the problem of different delay and power consumption requirements for terminal multi-scenario application services in LEO satellite IoT scenarios, this article proposes a method based on a simplified interaction process and Markov chain model for terminal work state switching. The method uses system downlink delay and terminal power consumption as Non-dominated Sorting Genetic Algorithms-Ⅱobjective functions to obtain a set of Pareto optimal solutions for multiple scenario frontiers. Furthermore, it selects working state timer parameters from the Pareto frontier to configure terminals online that meet different scenario delay and power consumption requirements.【Results】The simulation results show that the multi-objective optimization method proposed in this paper can globally optimize the timing parameters of the working state timer, and overcome the shortcomings of traditional methods such as exhaustive search falling into local optima. Additionally, it has been verified that simplifying the random access interaction process can effectively reduce terminal delay and power consumption.【Conclusion】The multi-objective optimization method proposed in this paper can obtain the working state timer parameters of the terminal in various scenarios of LEO satellite IoT.

【Objective】With the development of the sixth generation mobile communication technology, the inter-carrier interference in the traditional Orthogonal Frequency Division Multiplexing (OFDM) system makes the channel estimation performance insufficient to provide highly reliable communication, and Orthogonal Time-Frequency Space (OTFS) system can effectively solve the problem of communication system reliability degradation caused by fast time variability and Doppler effect, which has received wide attention in recent years.【Methods】In order to effectively meet the channel estimation performance requirements of OTFS systems, this paper uses an Optimized Generalized Complex Exponential (OGCE) Basis Expansion Model (BEM) to calculate the channel impulse response as a time-invariant basis function with basis function coefficients, which can effectively fit fast time-varying channels in high-speed mobile communication scenarios. The OGCE-BEM improves the spectral leakage by more intensive sampling and reduces the error of the high-frequency basis model by adding correction coefficients to reduce the error of the HF-based model.【Results】The simulation results show that the proposed algorithm is suitable for high-speed mobile communication scenarios with more reasonable design of the basis function. The estimation method has lower mean square error than the fixed forgetting factor, and the channel estimation results are more accurate. Compared with Least Square (LS), BEM-LS and BEM-Linear Minimum Mean Square Error (LMMSE) channel estimation methods, the performance of mean square error is significantly improved.【Conclusion】It can be seen that the channel estimation algorithm based on OGCE-BEM can effectively reduce the number of unknown parameters to be estimated and improve the accuracy of channel estimation.

【Objective】Replenishing the power supply system of an underwater communication system is usually very expensive and impractical. The underwater Simultaneous Light-wave Information and Power Transmission (SLIPT) communication systems based on solar cells are powerful solutions. However, the communication bandwidth of the silicon solar cell receiver is very limited, and it is easy to have the phenomenon of deep fading of the Signal-to-Noise Ratio (SNR) due to the underwater light attenuation effect.【Methods】For these problems, this manuscript employs a negative-biased solar cell light receiver scheme that increases the-3 dB bandwidth of silicon solar cells from 420 kHz to 768 kHz. Aiming at the deep fading of SNR caused by various degradation effects in the water environment, a Discrete Fourier Transfor (DFT) extended Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme with a low peak-average power ratio is adopted to offset the deep fading phenomenon in the system.【Results】The performance of DFT Spread OFDM (DFT-S-OFDM) and OFDM modulation systems in water environments with different turbidity (absorption and scattering characteristics) is compared. It is shown that the DFT-S-OFDM modulation and demodulation system is more robust.【Conclusion】Finally, experiments have shown that the total battery power efficiency of the energy harvesting system can be increased by 1.87 times under continuous illumination of white LEDs for 3 h, realizing synchronized energy harvesting in the communication process.

【Objective】In Free Space Optical (FSO) communication, atmospheric turbulence can cause a decrease in communication link performance.【Methods】In this paper, a polar coding channel coding scheme is proposed for this problem, and Monte Carlo algorithm is used to construct polar codes for Gamma-Gamma distribution atmospheric turbulence channels commonly used in FSO communication. By comparing the Block Error Rates (BER) of the proposed polar coding scheme, uncoded transmission, and Low Density Parity Check (LDPC) codes with similar code lengths under Gamma-Gamma distribution atmospheric turbulence channels.【Results】The simulation results show that when the Signal-to-Noise Ratio (SNR) is greater than 6.7 dB in weak turbulence, 10.3 dB in moderate turbulence, and 11.5 dB in strong turbulence, the proposed polar coding scheme performs better than uncoded transmission. Compared with LDPC codes, under weak turbulence conditions, when the SNR is greater than 7.1 dB, the overall performance of the proposed polar coding scheme is better than that of LDPC codes. Under moderate turbulence conditions, when the SNR is greater than 10.6 dB, the overall performance of the proposed polar coding scheme is better than that of LDPC codes. Under strong turbulence conditions, when the SNR is greater than 12 dB, the overall performance of the proposed polar coding scheme is better than that of LDPC codes. In addition, it is found that when the code length is short, the code rate is low, and the decoding width is small, the proposed polar coding scheme has better performance.【Conclusion】The use of the proposed polar coding scheme effectively improves the atmospheric turbulence effect in FSO communication systems. Moreover, in the harsh atmospheric turbulence channel environment of moderate and high turbulence intensities, the proposed polar coding scheme exhibits more obvious advantages than LDPC codes. This indicates that polar codes have good development prospects in FSO communication.

【Objective】Due to its comb filter characteristics, Sampled optical Fiber Bragg Grating (SFBG) has attracted wide-spread attention and become a new focus in the research of optical fiber grating technology. The research work on designing optical filters with high channel numbers, flat tops, and narrow pass bands is of great importance in practical situation. Consequently, an Multi-Phase Shift Interpolated Sampling optical Fiber Grating (MPS-ISFBG) filter is proposed.【Methods】ISFBG has a large number of reflection channels and can introduce multiple flat top narrow transmission channels by inserting multi-phase shift. By optimizing the location of the two π phase-shift distributions of the inserted ISFBGs, an optical filters with 41 transmission channels was designed which covers the C-band with a channel interval of 100 GHz. Each channel has a flat-top response, a narrow 3 dB bandwidth (

【Objective】The objective of this study is to investigate the resource allocation problem in Optical Wireless Communication (OWC) systems using Rate Splitting Multiple Access (RSMA) technique. We propose a joint precoding matrix and rate allocation algorithm based on linear approximation to enhance the system reliability and performance.【Methods】We employ variable transformation and linear approximation techniques to convert the non-convex fractional functions into convex ones. By using the joint precoding matrix and rate allocation algorithm, system resources can be effectively allocated to improve system performance. The optimization problem is solved using a continuous iterative algorithm to obtain the optimal solution.【Results】Simulation results demonstrate that the proposed joint optimization scheme significantly reduces the system outage probability and exhibits a fast convergence rate. This indicates that the proposed method can provide more reliable and efficient communication performance in the RSMA-OWC system, which is based on rate splitting access.【Conclusion】This study provides an effective resource allocation method for RSMA technology in OWC systems, enhancing system reliability and performance. Further research should focus on the challenge of system outage probability in RSMA-OWC systems, as well as resource allocation, precoding design, and application scalability. This study offers valuable insights to promote the application and development of RSMA technology in the field of OWC.

【Objective】This paper discusses full lifecycle energy efficiency of optical communication systems in the purpose of energy conservation and carbon reduction. It aims to establish a universal model for description of energy efficiency, which covers all stages of system lifecycle, and it is not limited to specific technologies or network structures. It also analyzes the key influencing factors for improvement of energy efficiency of optical communication systems.【Methods】This paper explores the useful work and energy consumption of optical communication systems, to establish a universal model for energy efficiency. In the expression of useful work, in addition to the commonly used factor data rate, distance factor is introduced as an important factor. The paper recommends that the value generated by data transmissions which meet specific quality requirements and maintaining network connectivity in specific scenario applications should be considered in the description of the useful efficacy. The description method is named as comprehensive useful efficacy. In the discussion of energy consumption, the system lifecycle is decomposed into four stages: manufacturing, installation and construction, operation and maintenance, and waste recycling. Main influencing factors of energy efficiency improvement are discussed based on the established model.【Results】Main results of the research include: (1) Distance factor can be one of the main factors for evaluating the useful work of a system, and distance factors affect energy consumption at various stages of the system's lifecycle; (2) For new scenarios and applications, setting weights for data transmissions which meet specific quality requirements and assigning values for maintaining connectivities status in description of the system useful work could reflect the value brought by the energy cost of the system to meet the needs of scenario applications; (3) Energy consumption factors of each stage of the life cycle should be considered in evaluation of energy consumption of the full lifecycle, and the energy consumption of each stage should be converted into unit time based on the system operating life for accumulation; (4) Optimized network topology and routing design, reduction of line losses, as well as evolution of optical transmission technology and equipment/facility energy saving technologies, are important means to reduce energy consumptions throughout the entire lifecycle of the system and improve the energy efficiency.【Conclusion】This paper discusses the comprehensive useful work and full life cycle energy consumption of optical communication systems, and establishes a universal model to describe the full life cycle energy efficiency of the system. This model takes distance as an important influencing factor in the expression of the useful efficiency and also energy consumption of the system, which corresponds the value of the optical communication system based on communication distance with the energy consumption in the life-cycle caused by distances. It also suggests considering the value generated by data transmissions which meet specific quality requirements and maintaining network connectivity in the evaluation of the useful efficiency. This model could comprehensively evaluate the energy efficiency of optical communication systems, for improvements of system energy efficiency, and could adapt and promote applications of optical communication systems in new scenarios.

【Objective】With the continuous advancements in satellite and communication technologies, the integration of space laser communication and ranging technology becomes more mature. As deep space exploration, satellite navigation, and other fields continue to develop, there is a growing demand for higher communication capacity and ranging accuracy between satellites. Thus, the need to achieve laser satellite high-speed communication while completing ranging and further improving ranging accuracy, under the premise of considering satellite payload and power consumption, has become an urgent issue.【Methods】This article designs and implements a coherent communication and ranging integrated system that supports both QPSK and BPSK, based on the principle of dual one way ranging. To further improve the ranging performance, the differential time sampling method is used to obtain the frequency difference and phase difference between the sending clock and the receiving clock through frequency and phase discrimination, thereby achieving higher clock accuracy and correcting the ranging value.【Results】The system can operate stably in an environment where the received optical power is greater than-48 dBm. Different rates can be set for different application requirements, with a maximum rate of 5 Gbit/s in QPSK mode and rates of 2.5 Gbit/s, 1.25 Gbit/s, and 625 Mbit/s in BPSK mode. The theoretical ranging accuracy of the system can reach a minimum of 53 ps. In normal communication, using Matlab and Vivado to calculate and process ranging data, the ranging accuracy of the system is verified to be less than 0.1 ns. Furthermore, using the differential time sampling method under simulation conditions, the ranging accuracy can be improved to the order of 10-3 of the symbol width, reaching±0.36 cm.【Conclusion】The proposed communication and ranging integrated system can achieve high-precision ranging while achieving high-speed communication, which is of practical significance for future applications of laser satellites.

【Objective】It is always difficult to timely locate the location of the network attack and achieve rapid deployment of defense strategies when the smart grid is attacked by the network.【Methods】In order to solve this problem, this article proposes a Convolutional Neural Network (CNN) model that integrates Convolutional Block Attention Modules (CBAM) (CNN-CBAM) to detect False Data Injection Attack (FDIA) positions. The attack identification problem of FDIA is modeled as a multi label classification problem, where CNN is used to extract spatial features of the data. The CBAM module can be directly integrated into the convolution operation of the CNN module, which not only focuses on important parameter information from the perspective of spatial domain, but also considers feature relationships in the channel domain, and allocates attention to the input data from two dimensions to improve the performance of the model.【Results】The performance of the proposed CNN-CBAM network FDIA position detection model is verified on Institute of Electrical and Electronics Engineers (IEEE) 14 and IEEE118 node systems. The experimental results show that the FDIA position detection rates of CNN-CBAM on IEEE14 and IEEE118 node systems are 98.25%and 96.72%, respectively.【Conclusion】Compared with other methods, the CNN-CBAM network model proposed in this paper can effectively extract the spatiotemporal characteristics between data, with improved existence of FDIA. It also im-proves the accuracy of attack location identification with better robustness.

【Objective】In Space Division Multiplexing (SDM) system, in order to achieve mode demultiplexing, it is necessary to adopt Multiple Input Multiple Output (MIMO) equalization scheme at the receiving end. As the number of transmission modes or transmission capacity increases, the computational complexity of MIMO increases significantly, resulting in high power consumption. Therefore, it is necessary to reduce the computational complexity of MIMO equalization.【Methods】We propose a frequency-domain joint equalization technique based on Cyclic Prefix (CP) to reduce the complexity compared with a traditional frequency-domain independent equalization and a separate dispersion compensation module in few-mode fiber short-range transmission systems.【Results】Based on the few-mode fiber model in VPI simulation platform, we build a 6×6 few-mode fiber transmission system to verify the advantage of computational complexity reduction of the proposed technology. The simulation results show that, the performance and computational complexity reduction of different CP ratios are also different. Under the same simulation conditions, when the proportion of CP is larger, the reduction of computational complexity is also larger, vice versa. With the same performance, the computational complexity of the frequency-domain equalization scheme with CP accounting for 11.11%is only 15.29%of that of the traditional frequency-domain equalization scheme based on block convolution.【Conclusion】Compared with the traditional frequency-domain equalization combined with a separate dispersion compensation module, the proposed frequency-domain equalization with CP has lower computational complexity.

【Objective】Traditional Free Space Optical (FSO) communication requires both ends of the communication to be installed at the same time, including the laser transmitting system, laser receiving system and acquisition, tracking and aiming system. It results in the problems of weight, volume, power consumption, and equipment complexity, thus limiting the development of FSO communication. Using the passive modulation technology constructed by asymmetric space laser communication link, the design of small volume, light weight and low power consumption of the communication terminal is successfully realized, which provides convenience for the application of small and medium-sized space laser communication technology.【Methods】In this paper, the research status of passive modulation at home and abroad is reviewed, which is mainly summarized abroad. In addition, the composition of the reverse modulation system and the working principle of the reverse modulator are described. Common Modulated Retro-Reflector (MRR) such as angle reflector reverse modulator and cat’s eye reverse modulator are analyzed. The selection of wavelength and the size of optical receiver aperture are discussed.【Results】This paper summarizes the different implementation types and characteristics of passive modulation, summarizes the application of passive modulation in FSO communication, and looks forward to the future development direction and prospect of this technology.【Conclusion】In the future, passive modulation can be developed along the direction of high speed, focal plane pixelation, two-way communication, coherent detection, and there is a lot of room for development. This paper can provide a reference direction for the research of passive modulation and a new idea for the research of FSO communication.

【Objective】When analyzing the nonlinear mutation frequency interference problem in all optical communication networks, interference detection mainly relies on estimating channel covariance directly, without expanding network communication signal transformation processing, resulting in low F1-score values of the detection results. Therefore, a nonlinear abrupt frequency interference detection algorithm based on finite difference time domain is proposed for all-optical communication networks.【Methods】We collect all optical communication network traffic data by combining packet capturing and mirroring methods, followed by cleaning, conversion, and protocol processing. Relying on the working principle of finite difference time-domain method, we first describe the time width and bandwidth of the signal in time-domain and frequency-domain space. Then we apply derivative and Fourier transform algorithm to transform the real-time collected network communication signal. Next, we use the transformed signal to analyze the nonlinear abrupt frequency interference. Finally the transformed signal is detected and analyzed. With the aid of the time-frequency joint feature analysis method, the time-domain and frequency-domain features of the interference signal are extracted. Relying on the back propagation algorithm and the minimization of the loss function, the detection process of nonlinear abrupt frequency interference is simplified. The characteristic distance function is used to replace the network loss function, and it is input into the interference recognition model based on the twin network to obtain the detection results of nonlinear abrupt frequency interference.【Results】The experimental results show that under different noise conditions, the F1-score value of the proposed algorithm's nonlinear mutation frequency interference detection results remains above 0.95. The detection time is less than 40 ms.【Conclusion】The new detection method using the finite difference time-domain method can more accurately reflect the interference situation of the current communication network. It ensures the normal operation of the communication network, and meets the interference detection requirements of all-optical communication network.

【Objective】In this paper, an ultra-low power consumption optical transmitter is developed to broaden the application of optical communication in short-reach interconnection such as board level and backplane level. The basic principle of the scheme is that the Vertical-Cavity Surface-Emitting Laser (VCSEL) laser generates an optical pulse signal after loading a bias current and a modulation signal through a Bias-T circuit.【Methods】In this work, the feasibility of the scheme is verified by means of simulation. It is also found that the main factors affecting the increase of the transmission rate are the parasitic parameters of the laser device and the impedance matching of the drive circuit. The two electrical transmission distances of 200 and 10 mm are studied by experiments. And the law of eye diagram quality and bit error rate as a function of driving voltage and bias current is studied through experiments under two electrical transmission distances.【Results】The results show that a larger effective extinction ratio ranging from 0.84 to 6.69 dB can be obtained by shortening the electrical transmission distance to 10 mm with the minimum differential driving voltage of 200 mV, the minimum bias current of 15 mA, and the power consumption of 1.2 mW/Gbit/s. Compared with traditional optical modules, the power consumption of optical transmission is reduced by about 80%.【Conclusion】This optical transmitter solution can be applied to intra-data center. Combined with low-power optical receivers, the overall power consumption of the data center can be significantly reduced.

【Objective】With the development of domestic optical network construction, the management of fiber optic cable routing resources increasingly attract the attention of operators, especially the problem of low efficiency in fiber optic cable survey. There is an urgent need for a feasible fiber optic cable survey method and plan to solve the current problems. The effectiveness and practicality of fiber optic cable routing survey methods are also important indicators that determine the improvement of network construction and maintenance indicators in the region.【Methods】The article investigates and analyzes the existing survey methods and laws of a large number of complex environmental optical cable routes. It also compares and analyzes the detection principles, application scenarios, and existing problems from multiple dimensions. The article focuses on evaluating efficiency improvement, operability, and cost. Combining with actual case situations, it analyzes the actual survey effects of different schemes in a targeted manner.【Results】The article innovatively proposes the research concept of a new fiber optic cable survey method and its application in multiple types of scenarios. The focus is on the practical application of cable identification instruments and cable knocking survey instruments that can be used for full process identification. They have advantages in efficiency and cost, and can solve the pain points of pipeline resource management for operators, providing ideas for the informational development and innovation of pipeline resources for domestic operators.【Conclusion】The method of fiber optic cable routing survey are important breakthroughs in effectively solving practical problems such as cable laying, cable inspection, and cable repair, which are important links in the construction of high-quality optical networks.

【Objective】For the problem of limited sensing distance of distributed optical fiber sensing system, a Phase-Sensitive Optical Time Domain Reflectometry (φOTDR)distributed optical fiber sensing system based on Remote Optically Pumped Amplifier (ROPA) technology was proposed.【Methods】Adopting polarization diversity reception technology to obtain orthogonal polarization signals to solve the problem of polarization mismatch, Frequency division band processing suppresses coherent fading and polarization fading. Applying high-order Raman pumping technology and cascaded ROPA technology, three remote gain units are selected with appropriate gain medium lengths. Introduced at the appropriate positions in the transmission link, the pump light and signal light are coupled and sent by the remote pumping unit to excite erbium ionst for unrepeatered amplification, realizing ultra long single span vibration signal sensing and solving the problem of insufficient single-span sensing distance of existing φOTDR.【Results】The experimental results show that In-phase and Quadrate (IQ) demodulation algorithm can be used to achieve linear recovery of Piezoelectric Transducer (PZT) disturbed 100 Hz signal.【Conclusion】The results show that this system can achieve vibration signal sensing of 176.6 km ultra long single span, breaking the existing φOTDR single span sensing distance recording. The vibration curve of the first 176 km is stable and the amplitude is below 0.4 rad. The undisturbed position in the three-Dimensional (3D) map is relatively stable, and the disturbance signal added by PZT at the end of the link can be accurately perceived. After Fast Fourier Transform (FFT) transformation processing, the signal-to-noise ratio of the 100 Hz disturbance signal is 8.9 dB. The experimental results are crucial for building ultra long single-span φOTDR sensing system and provides a certain reference value for the development of unrepeatered ultra long-distance sensing in OTDR systems.

In the field of optical communication, laser and its modulation bandwidth and modulation rate are very important for optical wireless communication. There are two main modulation modes for semiconductor laser signal: internal modulation and external modulation. These two modulation technologies have their own characteristics and are suitable for different fields of optical fiber communication. Internal modulation laser, also known as direct modulation laser, has become a cost-effective light source for the Fifth Generation Mobile Communication Technology (5G) fronthaul and data center because of its high-speed transmission and low cost. There is no additional Chirp of light source in external modulation laser, so the Composite Second Beat (CSB) distortion caused by fiber dispersion can be effectively overcomed. On the basis of reviewing the development history of communication laser and its modulation technology, this paper introduces the work and main progress made by Xi’an University of Technology in this field. This paper discusses the internal and external factors of nonlinear distortion of semiconductor laser, simulates the effects of various parameters of response characteristics, linearization compensation method and power control system on the output light source of light emitting device, and analyzes the influence of temperature fluctuation on the output power of laser and modulation device. Based on the basic theory of refractive index ellipsoid and numerical analysis, the variation trend of emitted light intensity with temperature is discussed under the longitudinal and transverse modulation, respectively. The results show that the variation trend of outgoing light intensity with temperature under longitudinal modulation is only related to the refractive index of Lithium Niobate (LN) crystal. Under transverse modulation, the variation trend of outgoing light intensity with temperature is affected not only by the refractive index of the crystal, but also by the crystal size and its expansion coefficient. Therefore, the special size crystal can be used to improve the temperature stability of the electro-optic modulator.

【Objective】High-frequency microwave carriers (GHz) with tunable capability have a wide range of applications in 5th Generation Mobile Communication Technology (5G)/ 6th Generation Mobile Communication Technology (6G) wireless networks, radar systems, and satellite communications. Due to the relatively simple structure of the system, the large bandwidth and the low loss, the technical scheme of generating high-frequency tunable microwave carriers based on photonic technology has attracted extensive attention from domestic and international research teams. Current photogenerated microwave experiments are mostly conducted in C-band wavelengths because of the mature commercial devices. Meanwhile, the Wavelength Division Multiplexing (WDM)-Radio Over Fiber (ROF) technology integrates the WDM technology with the ROF technology so as to flexibly realize the combining/splitting of microwave bands with the help of the combining/splitting of WDM system in the optical frequency domain. The ROF part of the system employs photogenerated microwave technology to simplify the base station configuration. Constrained by the limited bandwidth resources in the C-band wavelengths(35 nm, 1 530~1 565 nm), there is a drive for the generation of microwave to expand to wider spectral ranges. The U-band wavelengths can also provide channel bandwidths as wide as 50 nm (1 625~1 675 nm) to alleviate the channel utilization pressure in the C-band wavelengths; In the U-band wavelengths, Standard Single Mode Fibers(SSMFs) have achieved optical power loss as low as 0.195 dB/km (@1 625 nm); In particular, thulium-doped fiber amplifiers have also demonstrated a large bandwidth gain of 18.7 dB (@1 655 nm). These advantages attract SSMFs-based WDM systems to expand into the U-band, which leads to the extension of WDM-ROF technology into long wavelengths, and in turn leads to the expansion of photogenerated microwave technology. Therefore, this paper studies the photogenerated microwave technology in the U-band.【Methods】From the mathematical model, the commonly used photogenerated microwave carriers technologies are transparent to the applied optical carrier bands, and can be used to generate microwave carriers at arbitrary bands by selecting photonics devices corresponding to the operating bands. In principle, C-band wavelengths photonics devices (such as polarization controllers, Phase Modulator (PM), Fiber Phase Shifter (FPS), etc.) can work in the U-band, and the process technology of these devices is mature. Therefore, in this paper, photonics devices such as C-band wavelengths PM, FPS and optocouplers are used to build a photogenerated microwave carrier system based on U-band optical carriers.【Results】Finally, tunable microwave carrier with a tuning range of 7.5~12.0 GHz and a spurious rejection ratio of 29.6~35.2 dB is ultimately generated based on this system.【Conclusion】Through formula principle analysis and experimental verification, this paper extends the working band wavelengths of the photogenerated microwave carrier to the U-band wavelengths.

【Objective】Deformable Mirror(DM) is a key device in adaptive optics system for wavefront correction, and its performance directly determines the wavefront correction capability of the system. By studying DM and their control algorithm, the wavefront correction capability of adaptive optics system can be continuously improved. On one hand, the accuracy and response speed of DM can be enhanced to better correct various complex wavefront distortions. On the other hand, the control algorithm can be improved to increase the efficiency and accuracy of the correction. These studies will directly affect the imaging quality and performance of adaptive optics system. Therefore, investigating the DM and their control algorithm is of great significance for improving the wavefront correction capability, expanding application fields, and enhancing imaging quality and performance of adaptive optics system.【Methods】The article aims to summarize the research progress on DM and their control algorithm both domestically and internationally, as well as analyze the correction accuracy of different control algorithm for wavefront distortion, establishing the groundwork for the advancement of adaptive optics. Firstly, several typical DMs are used as examples to model the DM and provide detailed introductions to the structures and working principles of separate actuator DM, splicer DM, thin film DM, dual piezoelectric DM, Micro Electromechanical System (MEMS) DM and voice coil DM. Then, several control algorithms such as the Prandtl-Ishlinskii (PI) hysteresis model-based control algorithm, decoupled control algorithm, and sparse sampling control algorithm are analyzed.【Results】Summarized the work done by Xi'an Technological University in this field, and finally pointed out the future technological breakthroughs and improvement directions in this field.【Conclusion】The research progress on DM and their control algorithm lays the foundation for the development of adaptive optics, enabling its application in more fields and further improving the performance of adaptive optics system. This will help improve imaging quality and drive the development of adaptive optics technology.

【Objective】To meet the diverse application demands for high-performance Optical Frequency Comb (OFC), especially in terms of independently adjustable parameters like bandwidth, flatness, central wavelength, and spectral line spacing, a method based on secondary coupled Radio Frequency (RF) signals to drive a single Dual Drive Mach-Zehnder Modulator (DDMZM) for OFC generation is proposed.【Methods】Utilizing a single multiplier to generate the secondary RF coupled signals not only increases the number of comb lines produced by the OFC but also offers the advantages of a simple structure and low cost. Additionally, to further enhance the optimization efficiency and performance of the OFC, a deep learning-based inverse design and analysis approach is adopted.【Results】The study shows that the inverse design based on the constructed cascaded network can identify the corresponding parameters for the target OFC in less than one second. This rapid parameter determination method enables programmability of the number of comb lines, OFC power, and line spacing. It can also generate a 13-line OFC with a flatness of 1.769 dB. This efficient design method provides robust support for the rapid preparation and application of OFCs.【Conclusion】The proposed solution in this study demonstrates significant advantages in OFC generation technology, particularly in performance, flexibility, and optimization efficiency. The method of generating OFC through DDMZM driven by secondary coupled RF signals not only simplifies the system structure and reduces costs but also significantly improves design efficiency through the reverse design approach of deep learning. These characteristics make this solution suitable for a wide range of applications, especially in scenarios requiring quick, efficient, and flexible adjustment of OFC parameters.

【Objective】In response to the needs of Ultra High Voltage (UHV) site infrastructure control and intelligent transportation and inspection, 5th Generation Mobile Communication Technology (5G) is applied to the construction phase of UHV converter station for the first time in China.【Methods】On the basis of realizing 5G full coverage of Henan southern converter station, 5G virtual private network of converter station is built and the Mobile Edge Computing (MEC) cloud platform is deployed. Fully considering the needs of early infrastructure and late operation, the intelligent infrastructure site is connected with the intelligent converter station in the later stage. Relying on the advantages of 5G and integrating Artificial Intelligence (AI) and other technologies, various types of data on the construction site of UHV infrastructure can be collected in real-time and unified, providing multi-functional 5G solutions for remote video monitoring of UHV infrastructure, engineering monitoring and early warning, panoramic presentation of infrastructure site, identification of safety hazards, and expert remote assistance guidance. 5G applications such as smart construction site, intelligent inspection and intelligent control are organized and 5G network adaptation test is carried out.【Results】Providing a flexible, large-bandwidth and high-speed communication methods of 5G for the business application of Henan southern converter station. It effectively enables various business requirements in the UHV converter station, verifying the carrying capacity of 5G for UHV construction and inspection services. It also improves the management efficiency, and reduces the operation and maintenance cost.【Conclusion】The successful application of 5G in the Henan southern UHV converter substation provides a typical UHV substation solution of 5G+ energy Internet, which verifies the feasibility of 5G in the power industry and also promotes the application of 5G in power scenarios.

【Objective】In order to improve the confidentiality and performance of the mixed Radio Frequency (RF)/Free Space Optical (FSO) communication systems, it is necessary to study the security performance of the Reconfigurable Intelligent Surface (RIS)-assisted mixed RF/FSO system to obtain the relationship between system security performance and parameters such as RIS deployment location and the degree of correlation between different antennas branches.【Methods】In the article, a single eavesdropper is considered to eavesdrop against RF links and FSO links respectively, with RF links obeying an arbitrarily correlated Nakagami-m distribution and FSO links obeying a Gamma-Gamma distribution. Closed expressions for the Security Outage Probability (SOP) and Strictly Positive Security Capacity (SPSC) probability of the communication system for the two eavesdropping scenarios are derived using the decode-and-forward protocol, and the SOP is analyzed asymptotically. Simulation experiments are also conducted using the Matlab software to verify the accuracy of the derived formulas through Monte Carlo simulation.【Results】Simulation results show that deploying the RIS close to the receiver reduces the security outage probability of the system. It is also shown that an increase in the degree of antenna correlation increases the SOP of the system when the channel quality of the RF main channel is better compared to the eavesdropping channel.【Conclusion】The RIS-assisted FSO link has better security compared to the RF link. Although the multi-antenna diversity technique can effectively improve the security performance of the system, antenna correlation, similar to the fading caused by pointing error and atmospheric turbulence, can also damage the security performance of the system. It is also shown that the security of the system can be effectively improved by reducing the degree of antenna correlation.

Liquid Crystal-Spatial Light Modulators (LC-SLM) control the optical path by modulating the refractive index of liquid crystal, and play an important role in adaptive optics. This paper sorts out the development status of LC-SLM at home and abroad, and introduces the working principle and phase calibration principle of LC-SLM in detail. Aiming at the application of LC-SLM in adaptive optics, the research status of key technologies of LC-SLM at home and abroad is discussed. The experimental research in this field of Xi'an University of Technology is analyzed and summarized. Finally, the application status of LC-SLM is prospected.