As a temperature sensor, fiber Fabry-Perot (F-P) cavity sensor is widely used. Improving the photoelectric properties of the materials and components of the optical fiber is conducive to improving the sensitivity of the temperature sensor.A F-P temperature sensor based on SiGe core fiber is prepared based on fiber fusion and polishing technology. The preparation process comprises the following steps: firstly, splicing the general single-mode fiber with the SiGe core fiber by using optimized splicing parameters, and then polishing the SiGe core fiber by means of optical fiber polishing, the length of which can be precisely controlled by observing the free spectrum range of the reflection spectrum during the polishing process. The experimental results show that the spliced end face is smooth and flat, and the intensity of the reflection spectrum is 7.7 dB higher than that of the single-mode fiber. The SiGe core optical fiber F-P cavity sensor has a high temperature sensitivity, which can reach 116.1 pm/℃.

In order to realize precise sampling of high-precision distributed temperature sensor, a temperature sensor system based on dynamic oversampling technology of fiber Raman scattering is discussed in this paper. The system realizes spatial dynamic oversampling of Stokes signal and anti-Stokes signal by using the method of dynamic adjusting sampling clock phase shift of field programmable gate array(FPGA). It realizes four times spatial oversampling of 250 MHz sampling clock. The equivalent sampling rate reaches 1 GHz. The method can capture nanosecond scattered light pulses well and has the ability of temperature detection with long distance and high resolution.

Aiming at the problem that the phase sensitive Φ-optical time domain reflectometer(Φ-OTDR) system can't locate the two adjacent sources whose spacing is less than its pulse width, this paper analyzes the high-order harmonic characteristics ofΦ-OTDR signal and its spatial distribution characteristics under the condition of two adjacent sources, and proposes a location method based on the bispectrum marginal spectrum. This method can improve the locating ability of Φ-OTDR without any additional hardware. The experiments show that this method can separately locate two vibration sources with 5 m interval under 200 ns probe pulse (means 20 m spatial resolution) and it can work no matter the same or different frequencies the two vibration sources are. This work will help the application of Φ-OTDR system in pipeline safety monitoring and structural health monitoring.

Water disasters in coal mining often bring a variety of huge losses, but it is difficult to monitor water seepage in coal mines. Based on the principle of optical fiber microbending loss and the optical time domain reflection(OTDR) technology, this paper presents a method of detecting and locating mine water seepage. Combined with the water expansion characteristics of expansive soil waterproof mat (GCL), GCL in the water seepage zone expands and conducts deformation to the fiber tightly attached to the outer diameter. The detection results of water seepage can be obtained through the principle of optical fiber micro-bending loss. At the same time, combining with the principle of OTDR, the deformation point of bending loss, namely the water seepage point, can be positioned. The experimental shows that the seepage location is basically consistent with the measured results and the method has a good location effect.

Aiming at the problem of huge amount of information generated by long-distance oil and gas pipeline early warning signal and accurate identification of early warning signal, an early warning system was proposed, which core components of the hardware platform is field programmable gate array (FPGA) and digital signal processor (DSP), the control of high-speed collection of early warning information is mainly accomplished by FPGA, the fast processing of high-volume information and precise recognition algorithm of early warning signal is mainly accomplished by DSP, data transmission between FPGA and DSP is carried out through high-speed interface to realize rapid and accurate alarm for pipeline intrusion. Completed the design of each functional module of the host computer and slave computer, the software system is designed with C# development language, and the real-time monitoring of pipeline system is implemented by means of communication of network protocol. Finally, the feasibility and accuracy of the system are proved by experiments.

The influence of incident optical power on the transmission distance tolerance of high-rate communication is analyzed. In order to solve the problem which limits the incident optical power, a system solution based on remote Er-doped amplification technology(REOA) is proposed, which improves the equivalent incident optical power and the transmission distance tolerance greatly. It is theoretically analyzed that the equivalent incident optical power is related to the loss of the fiber in the front of REOA and the output power of REOA. The experiment of 400 Gb/s transmission demonstrates that the equivalent incident optical power of REOA system is 14.27 dB higher than that of conventional system, and the transmission distance is extended by about 70 km.

In synchronous digital hierarchy(SDH) , pointer adjustment during positioning will cause great jitter of output signal. In order to ensure the quality of signal, a de-synchronization circuit which is used in the receiving end of E1 tributary in SDH is proposed. The circuit contains an adaptive filter and a second-order digital phase-locked loop(PLL) with medium bandwidth. The numerical control oscillator in PLL consists of a serial accumulator and a dual-mode divider. It adopts the method of frequency discrimination and phase discrimination in parallel, and uses a digital filter. By establishing mathematical model, its working process and output jitter are analyzed. Simulation results show that the performance index meets the related standard of ITU-T.

The cost and backward compatibility are the key factors for next passive optical network(PON) evolution after commercial 10G PON readiness. To leverage the investment from operator for current optical distribution network(ODN) deployment and support co-existed PON system, this article focuses on the technical solution at physical layer for 25G PON with relevant cost control based on time division multiplexing(TDM) mode related with single wavelength. To support 50G PON evolution, it briefly introduces the characteristics of modulation scheme and the newly introduced digital signal processing (DSP) technology. Finally, it summarizes the latest industrial situation and gives the forecast evolution of 25G and 50G PON.

Aiming at the difficulty of the coarse tracking control technology of free space optical communication system, a cascade coarse tracking control structure is designed. A linear auto disturbance rejection controller is introduced, and the linear extended state observer is used to observe the total disturbance of the system. The simulated dynamic tracking experiment is carried out to compare the control errors of the linear auto disturbance rejection controller and the proportional integral differential controller under the disturbances of 0.5 Hz, 1 Hz and 2 Hz. The experimental results show that the linear auto disturbance rejection controller has higher control precision and better stability.

In order to solve the problem of channel fading caused by multipath effect and communication interruption caused by occlusion of receiver in visible communication system, the diversity receiving technique was employed as the solution to improve communication quality. Considering the complexity of the receiver and the performance-cost ratio of the system implementation, the selective combination treatment which is relatively simple but also has the advantage of diversity was introduced at first. Secondly, after analyzing the number of branch selection combining mode, 4-road gate circuit was selected as diversity receiving signal processing circuit. Finally, the circuit simulation and physical testing was completed. The results show that the diversity receiving technique increases 10 dB signal to noise ration(SNR) of the receiver as compared with the receiving system without diversity circuit receiving device.

The response speed of the white light emitting diodes(LED) affects the modulation bandwidth of the communication link and directly limits the data transmission rate of the white light communication system. In order to improve the communication rate when the modulation bandwidth is limited, a variable-period modulation white light communication system is designed. The data source is generated by the microcontroller at the transmitting end of the system, and the data is framed and modulated by a field programmable gate array (FPGA), and transmitted through the driving circuit and the LED light source. The FPGA at the receiving end of the system demodulates the digital signal output through the photodiode and the signal conditioning circuit. The experimental results show that the system effectively increases the data transmission rate compared to digital baseband modulation such as on-off keying, pulse position modulation, and differential pulse position modulation.

Nonlinearity is an important factor limiting the transmission performance of visible light communication (VLC) systems. Although orthogonal frequency division multiplexing (OFDM) technology can effectively improve the spectral efficiency of VLC, it also makes systems more sensible to nonlinearity due to its high peak-to-average power ratio. This paper proposes a post distortion method based on long short term memory(LSTM) network, which takes the local correlation of signals into account and can effectively compensate linear and nonlinear transmission impairments in VLC systems. In the case of line-of-sight transmission, compared with the post-distortion based on linear recursive least square, simulation results show that Volterra series and memory polynomials, the post distortion method based on LSTM not only can improve the performance of error vector magnitude, but also can increase signal bias voltage and dynamic range and decrease the demand for signal and noise ratio by about 4 dB with the same bit error rate.

The internal structure and materials of photonic crystal fibers (PCF) have an important influence on the transmission characteristics. The simulation model of PCF can optimize the design of optical fibers quickly and effectively and shorten the development cycle. Using full vector finite element numerical simulation method, the control mechanism of structural parameters on PCF's mode characteristics, birefringence, nonlinearity, effective area, limiting loss and dispersion is studied. By adding and optimizing axisymmetric distributed elliptical air holes, birefringence of 1.39×10-2, limit losses of 10-7 magnitude, nonlinearity of 37.98 W-1·km-1(in HE■■), 44.39 W-1·km-1 (in HE■■) at 1.55 μm is obtained. The a dispersion value of -1.3±0.3 ps/(km·nm) is achieved within the wavelength region 0.8~2.0 μm with flat and approximately zero dispersion.