Phase-sensitive optical time domain reflectometer (Φ-OTDR) is widely used in the field of distributed vibration monitoring due to its long sensing distance, simple laying, corrosion resistance and anti-electromagnetic interference. With the diversification of sensing tasks and the wide application of artificial intelligence, the type recognition of vibration events has become a hot research direction. In order to enable readers to better understand the research progress and development trend of recognition classifiers, this paper introduces the traditional recognition classifiers and the neural network recognition classifiers based on deep learning, compares the performance indexes, advantages and disadvantages of different classifiers and their applications, and finally prospects the research direction of Φ-OTDR vibration event recognition.

Aiming at the unknown fatigue performance of fiber Bragg grating(FBG) strain sensors used in crane structure health monitoring, the fatigue performance of three packaged FBG strain sensors used in crane structure fatigue damage monitoring is studied by combining dynamic load with static tensile test method. The sensitivity coefficient, bandwidth, edge rejection ratio, peak-valley ratio, zero-point wavelength and dynamic strain of the sensor are analyzed with the increase of fatigue frequency. The test results show that before and after fatigue, when loading and unloading the same load, the difference of sensitivity coefficients is no more than 0.1 pm/με, the mean bandwidth is 0.19 nm to 0.23 nm, the peak to trough ratio and edge rejection ratio change with the increase of fatigue frequency, and the maximum change of zero wavelength is 0.31 nm. The dynamic strain conforms to the distribution characteristics of quadratic exponential function.

Aiming at the complex structure and high design cost of traditional meter scattering lidar, a portable meter scattering lidar system for detecting atmospheric aerosols is proposed. First, the optical system structure of coaxial transceiver is designed, and then the photoelectric detector is designed independently. Finally, based on the system structure, a movable meter scattering lidar experimental platform is built to preliminarily detect atmospheric aerosols. The experimental results show that after filtering with the designed power filter, the original ripple voltage range of switching power supply is reduced from 0.1 V to 0.0 1 V, and the noise amplitude is controlled at about 0.1 V. The oblique detection distance of the system in the day and night is 4.5 km and 6 km respectively, which can monitor the aerosol in a specific area in real time.

Aiming at the problems of weak atmospheric echo signal and large noise interference detected by Doppler wind lidar, a semi-soft threshold algorithm based on wavelet transform is proposed. Firstly, the principle of semi-soft threshold algorithm based on wavelet transform is analyzed. The incoherent Doppler wind lidar system with Mach-Zehnder interferometer as frequency discriminator is built. Then, three algorithms of hard threshold, soft threshold and semi-soft threshold are used to test the echo signal detected by laser radar. The experimental results show that compared with other threshold methods, the signal-to-noise ratio(SNR) of semi-soft threshold is 4.933 5 dB and the root mean square error(RMSE) is 0.676 2. The denoising effect is better and the detection accuracy of atmospheric wind speed is effectively improved.

In order to reduce the complexity of the sensor structure and improve the sensitivity of the sensor temperature, a dual-side throw D-type photonic crystal fiber surface plasmon resonance(SPR) temperature sensor with regular hexagon and regular octagon cladding is proposed. By using COMSOL multiphysics finite element simulation software, the influence of polarization direction, air aperture and silver film thickness on the performance of the sensor is studied respectively, and the optimal value of each data is found out. Based on this, the temperature sensing characteristics of the sensor are analyzed. The simulation results show that when the cladding air hole d1=1 ?滋m,d2=0.5 ?滋m, and the thickness of the metal silver film tAg=35 nm, the performance of the sensor is the best, and the maximum temperature sensitivity of the sensor can reach -7.99 nm/℃ at 0~120 ℃.

In view of the low sensitivity of existing optical fiber sensors in measuring temperature and magnetic field intensity, a optical fiber temperature and magnetic field sensor based on optical signal is proposed. The sensor designed has a long period fiber grating (LPFG) cascaded short period fiber Bragg grating (FBG) as the sensing structure. The magnetic fluid is used as magnetic sensitive material. The sensitivity is improved by using HF solution to etch the optical fiber cladding. Firstly, the principle of measuring temperature and magnetic field intensity by this sensor is introduced. Then, the LPFG-FBG sensor structure is simulated by using Optigating simulation software. Finally, the sensor is desinged and the experiments of measuring temperature and magnetic field intensity is conducted according to the simulation results. The experimental results show that the sensitivity of the sensor is 85.7 pm/℃ when the temperature is 35~85 ℃. When the magnetic field intensity ranges from 4~20 mT, the sensitivity of magnetic field intensity is 65 pm/mT, and the stability is good.

Aiming at the problems of high cost and complex structure of optical fiber sensing systems using traditional self organizing fiber lasers, a optical fiber Michelson interferometer(FMI) sensing demodulation system based on the strong feedback of a commercial laser is proposed. The system adopts a commercial Fabry-Perot cavity semiconductor laser diode(FP-LD) as the light source, directly driven by direct-current power supply, and form strong feedback on the FMI after reflection and interference. Multi-longitudinal mode laser beat frequency demodulation technology is used to realize the sensing demodulation of FMI. The change of FMI optical domain interference light intensity is directly converted into the change of electric domain beat frequency envelope. The change process of beat frequency signal with temperature and the sensitivity of sensing system with different FMI arm length difference are studied. The experimental results show that when the arm length difference is 0.45 m and 0.40 m, the sensitivity is 325 kHz/℃ and 358.33 kHz/℃ respectively.

Distributed optical fiber vibration detection based on phase sensitive optical time domain reflectometer(OTDR) is an important protection method for early warning of submarine cable anchor damage. Aiming at the requirements of distinguish intrusion event types for detecting anchor damage of submarine cable, the backpropagation(BP) neural network classifier is applied to the submarine cable anchor damage prevention system based on Φ-OTDR. The principle of the submarine cable anchor damage prevention system based on Φ-OTDR+BP neural network classifier is introduced. The characteristics of signal in time domain and time frequency domain are used as feature vectors. A classifier based on BP neural network is constructed to recognize the types of intrusion events. The experimental results show that the pattern recognition accuracy of the classifier reaches 100%.

In order to ensure the accuracy of high temperature distributed temperature measurement in oil and gas wells, a high temperature single mode Raman self-calibration monitoring system is designed. The working principles of the distributed Raman temperature measurement system and the fiber grating temperature calibration system in the system are introduced, and the high temperature monitoring experiment of 800 ℃ is carried out for the temperature measurement range and accuracy of the system. The experimental results show that the temperature resolution of the system is 0.1 ℃ and the temperature measurement accuracy is ± 2 ℃ under the condition that the temperature measurement distance is 0~1 km and the temperature range is 0~800 ℃, which basically meets the requirements of high temperature distributed temperature monitoring.

In the layered asymmetric clipped optical orthogonal frequency division multiplexing (LACO-OFDM), the use of discrete Hartley transform(DHT) can makes up for the low spectral efficiency of fast Fourier transform (FFT), but there is still a problem of high computational complexity in the separation of multi-layer signals at the receiving end. Combined with the time-domain symmetry and anti-symmetry characteristics of the DHT-LACO-OFDM signal, a layered signal receiving method based on time domain reconstruction is proposed, in which the superimposed signal is received layered in the time domain. The results of the study show that, compared with the traditional iterative receiving method combining time-frequency domain, the layered signal receiving method based on time-domain reconstruction has almost the same bit error performance as the traditional iterative receiving method, but the computational complexity is reduced by half.

The development of high-power, high-energy, high-efficiency terahertz radiation sources that can operate stably at room temperature is a practical problem that urgently needs to be solved in the field of terahertz technology. Based on the transient photocurrent model, this paper studied the physical process of three-color laser pulse-induced terahertz waves in liquid media by numerical simulations, and analyzed the effects of phase difference, intensity ratio, wavelength, and pulse width on the terahertz radiation. The simulation results show that the phase differences, the intensity ratios, the wavelength and the pulse width have obvious effects on the terahertz electric field. At the same time, only the tunnel ionization mechanism in which the ionization rate changes with the oscillation of the laser electric field can generate transient photocurrents, thereby obtaining terahertz radiation.

In order to effectively reduce frequency spectrum fragmentation and blocking probability in elastic optical networks, a spectrum allocation algorithm based on graph coloring model is proposed. Firstly, a graph coloring model is established for elastic optical networks, and the spectrum allocation problem is transformed into a graph coloring problem with weights. Then, two improved coloring algorithms(chain search method and improved greedy algorithm) are proposed. The simulation results show that compared with the degree maximum coloring algorithm, the two improved coloring algorithms can better optimize the spectrum resources and reduce the average blocking probability.

Aim at the distributed measurement requirements of high-speed rotating equipment, a single-channel fiber optic rotary joint(FROJ) is designed and its performance is tested. Based on single-channel FROJ, four-channel FROJ is designed by magneto-optical switch, and its insertion loss is tested under static and dynamic conditions. The experimental results show that the insertion loss of the four-channel FROJ is less than 4.5 dB, the rotation variation is less than 2 dB, and the reliable optical signal transmission can be realized when the speed does not exceed 600 r/min.

In order to increase the output bandwidth of Raman fiber amplifier(RFA) and reduce the gain flatness. The relationship between the gain characteristics and the pump source under different parameter settings is analyzed by using OptiSystem software. The pump power, pump wavelength, fiber length and effective area are optimized and simulated. The simulation results show that the proposed optimization method can maximize the gain of RFA within the set range, and obtain better gain flatness by changing the relevant parameters.

In order to solve the problems of irregular wiring of optical fiber jumpers in optical distribution frames and excessive redundancy of optical cables in traditional communication rooms and data centers, an intelligent checking system for optical fiber routing is proposed. Firstly, the optical transceiver system is controlled by a high-performance and low-cost microcontroller STM32 chip, and the optical fiber routing is checked through the electro-optical signal data transceiver. Then, based on general operational amplifier LM358 and relay technology, quantitative amplification and relay processing are designed. Finally, the OptiSystem software is used to simulate the performance of the system. The test results show that the maximum dynamic range of the system is 9.24 dB, and it can achieve the troubleshooting function with an optical fiber transmission distance of 46 km. At the same time, the quality of the regenerated signal in the system has been improved, which can effectively extend the transmission distance of the system.

In order to explore the mechanism of IQ imbalance, combining polarization multiplexing(PDM), hexadecimal orthogonal amplitude modulation(QAM), phase conjugate twin waves(PCTW), orthogonal frequency division multiplexing(OFDM), wave division multiplexing(WDM) and other technologies, this paper uses OptiSystem software to build PCTW-OFDM-WDM system. The mechanism of IQ imbalance caused by probabilistic shaping, crosstalk and statistical correlation noise is analyzed. The theoretical analysis and simulation results show that IQ imbalance is caused by many factors, and only a large IQ imbalance will have a significant impact on the system performance. Geometric shaping scheme has limited effect on IQ imbalance and performance improvement. In the time slot and subcarrier PCTW mode, appropriately changing the location of the distribution of the conjugate components can effectively improve the IQ imbalance and obtain better transmission performance than adjacent structures.

High speed real-time digital multi beam forming system mainly uses optical fiber transmission technology to transmit data, however, optical fiber may be limited by size, luminous decay, price, installation, etc. The introduction of high-definition digital video transmission technology can effectively solve this problem. This paper proposes a coaxial cable multi-beam data transmission scheme, which consists of high-speed serial transceiver, driver, equalizer, etc. Its principle is to achieve high-speed transmission of multi-beam data based on serial digital interface technology. Simulation experiments and physical tests have been carried out, and the simulation and test results show that this scheme can achieve the same performance as the optical fiber transmission scheme.