Orthogonal frequency division multiplexing(OFDM) technology can improve the communication rate of visible optical communication system and suppress intersymbol interference, but it also produces high peak-to-average power ratio (PAPR) and non-linear distortion. In order to solve this problem, researchers have used PAPR suppression technology to reduce the high PAPR of OFDM signal. This paper summarizes the research progress of PAPR suppression technology in visible light communication system in recent years, and divides them into three categories in principle: PAPR suppression strategy based on signal limiting, PAPR suppression strategy based on probability selection and PAPR suppression strategy based on signal precoding. The performance of these three kinds of PAPR suppression strategies is simulated, analyzed and compared, their advantages and disadvantages are summarized, and the applicable occasions are discussed, and the future work is prospected.

In order to improve the security of the visible light communication system and further reduce the bit error rate of the system, chaotic sequences with pseudo-random characteristics, spread spectrum techniques, and pulse position modulation (PPM) are introduced into the light-emitting diode (LED) optical communication system. An LED optical communication system based on chaos pulse position modulation (CPPM) is realized. Under the additive white Gaussian noise(AWGN) channel, the influence of signal-to-noise ratio(SNR) on bit error rate of PPM system is analyzed. At the same time, the influence of the key, SNR and the length of chaotic sequence on the bit error rate of CPPM system are analyzed. Simulation results show that when the length of chaotic sequence is greater than 32, the CPPM system is superior to the PPM system, which can reduce the bit error rate of the system and improve the security of the system.

With the increase of software defined optical network(SDON) scale, multiple controllers are needed to provide services for the whole network. The load balancing problem of controllers affects the service capability and network survivability of the whole network. A self-learning load balancing algorithm for SDON controller based on Bayesian network is proposed. Firstly, considering the controller parameters such as controller load, controller throughput and optical switch migration delay, Bayesian network is used to predict the degree of load congestion; secondly, the optimal action decision is made by combining reinforcement learning algorithm, and the feedback mechanism is used to realize the self-adjustment of parameter weights so as to adjust the control. Load balancing can be achieved by the degree of load congestion. The simulation results show that compared with Q-learning algorithm, the proposed algorithm achieves better load balancing function of the controller and improves load balancing efficiency more quickly.

To cope with the problem that complex signaling interaction process will greatly increase the satellite network time delay, this paper draws on the research of terrestrial optical network signaling and put forward a novel optical burst switching network signaling based on intermediate-node prediction. The network performance is analyzed and verified by simulation. The signaling adds model prediction mechanisms to intermediate nodes of links. It dynamically selects the optimal intermediate node for signaling confirmation based on predicted network performance indicators. The simulation result shows that the method can balance time delay and blocking rate of services, so that the performance of all aspects in the satellite network will not deteriorate sharply.

High-power ultra-short pulse sources are widely used in information, precision machining, medical, defense, and basic scientific research. Aiming at the increasing trend of high power demand in various fields, the mainstream technologies for achieving high peak power are introduced from three aspects of seed source, amplification technology and stacking technology. The implementation methods of important new technologies such as new mode-locked lasers, new amplifiers and various pulse stacks and the research progress at home and abroad are introduced. Finally, the future implementation of ultra-high power technology is predicted and forecasted.

In order to realize the function of wavelength division multiplexer with compact structure and high transmissivity, a high efficient three-channel wavelength division demultiplexer based on the energy band characteristics of photonic crystal is presented. Based on the plane wave expansion method(PWE), the propagation characteristics of photonic crystals are analyzed and the band gap of photonic crystals is given. The finite element method(FEM) is used to optimize the structure parameters of the device and the transmission spectrums of different ports are given. The experiment results show that the proposed device is able to drop three channels at resonance wavelength of 1537.8 nm, 1543.7 nm, 1548.7 nm. The transmission of output ports both reach 90%, the average channel spacing is about 5.5 nm, and the average value of the crosstalk between output channels is about -27 dB. Besides, it has high coupling efficiency, good wavelength selectivity, low value of channel spacing and crosstalk. At the same time, the wavelength adjustment method is simple and easy to integrate.

In order to detect the pH value of liquid easily, the pH sensitive sol-gel film was coated by chemical etching in the corrosion area after stripping the multi-mode optical fiber. Then a Mach-Zehnder interferometer pH detection sensor based on core mismatch was fabricated. Spectrometer was used to detect the response spectrum of the sensing structure to pH sample solution, and the response spectrum data were analyzed. The results show that when the pH value of the sample solution is in the range of 4.02~10.01, the wavelength shift of the response spectrum and the change of the pH value show a good linear law. The center wavelength of the detected trough drifts to short wave direction by 567 pm for each unit of pH change. At the same time, the sensing structure has good mechanical strength after coating, and can be better applied to the detection of liquid pH.

The divergence of spontaneous radiation of fluorescent molecules and low radiation efficiency limit the capture of optical signals in single-molecule fluorescence sensing, and dielectric nanocylinders can effectively improve the directional luminescence intensity of fluorescent molecules. By the finite difference time domain (FDTD) method, it is theoretically studied that the oscillation direction of fluorescent molecules, the distance between the fluorescent molecules and nanocylinders, the refractive index of nanocylinders and the diameter of nanocylinders influence the directional luminescence enhancement. The results show that when the refractive index of the nanocylinder is 1.7, the oscillation direction of the fluorescent molecule is along axial direction of the cylinder, the nanocylinder has a larger diameter and the distance of the fluorescent molecule from the nanocylinder is smaller, the fluorescence directional enhancement effect is better. When the diameter of the nanocylinder is 1 μm and the fluorescent molecule is 10 nm from the nanocylinder, the fluorescence directional enhancement is about 10 times and the directional emission angle is about 16.1°.

With the higher and higher requirements of micro-electro-mechanical-systems(MEMS) inertial sensors for micro-displacement detection precision, micro-displacement detection technology has become a research hotspot in the field of MEMS inertial sensing. The emergence of sub-wavelength gratings provides a new development prospect for micro-displacement measurement. In this paper, the off surface double-layer sub-wavelength grating displacement sensing system is studied. The displacement sensing characteristics of the system of equal period and unequal period are studied. The relationship between the transmittance of diffracted light and the off surface double-layer displacement of the dual sub-wavelength gratings and the influences of the key structural parameters of the system on the sensitivity of the displacement detection are simulated by Rsoft software. The structure optimization and performances of the two dual grating micro-displacement sensing systems are simulated and compared. The high sensitivity advantage of sub-wavelength grating displacement detection is verified in theory.

The amplitude variation of the coherent optical time domain reflectometer(COTDR) measurement curve is greatly affected by coherent Rayleigh noise, which leads to system false alarms and system performance degradation. The paper describes the mechanism and influencing factors of coherent Rayleigh noise in COTDR system, the quantitative relationship between each factor and the Rayleigh scattering coefficient is given, and simulates the impact of the fiber refractive index, spatial resolution and the frequency variation of laser source on the interference fading waveform in detail. Finally it summarizes the main methods and limitations of reducing the interference fading in view of changing the laser frequency in COTDR system. Several important applications of COTDR are given, including the monitoring of ultra long communication optical fiber link and the subway tunnel.

In recent years, photon frequency conversion technology has become a research hotspot that breaks through the key performance indicators of microwave signal frequency conversion. However, the inherent working state of photon frequency conversion is not stable, which makes the technology difficult to be applied. A photon frequency conversion control system for a single electro-optic external modulator is designed, which is specially used to realize the fast, accurate and micro disturbance regression after the best photon frequency conversion working point drifts. The system takes advantage of the comprehensive advantages of hardware and software, extracts the micro variable parameters of the photon frequency conversion working point by the calculus algorithm, and returns the drift working point to the best frequency conversion working point quickly and with micro disturbance by the proportion algorithm of control variables.

Signal generation with special time domain waveforms is an important research content in the field of microwave photonics and has been widely used in various fields such as military and civilians. This paper briefly introduces several specific optical function waveform generation technology based on frequency-domain synthesis and time-domain synthesis. The advantages and disadvantages of the frequency-domain synthesis and time-domain synthesis are compared and analyzed. At the same time, several introduced technology are compared and summarized from the tuning ability of the waveform repetition frequency, the waveform duty ratio, the multiplication factor, the system application and the system structure of the signal generator.