Fire poses a great threat to people's production and life, but existing fire sensors have limitations in installation space, measurement range and applicable environment. Therefore, it is necessary to develop new types of fire sensors. This paper designs and implements an industrial fire warning optical fiber sensor that is reliably encapsulated by a stainless steel capillary tube. This paper greatly improves the high temperature resistance of traditional fiber grating sensors through high temperature regeneration processing of fiber gratings. Experiments on the prepared sensor show that the sensor can measure temperature up to 1000 ℃, linearity is 0.99951, and the response time of 90% signal at 1000 ℃ is less than 3 s, it is suitable for fire warning.

It is very important to detect the fiber Bragg grating(FBG) wavelength accurately for engineering monitoring in bad environment. This paper reviews the methods of improving wavelength demodulation accuracy and wavelength signal processing in different demodulation systems. It mainly introduces the research progress of demodulation system based on tunable laser, tunable filter and spectrometer to improve wavelength calibration accuracy, analyzes the influence of the algorithm in the process of signal demodulation on the demodulation performance of FBG sensor.

According to the current situation of optical fiber sensors, the characteristics, advantages and application fields of distributed and quasi distributed optical fiber sensors are briefly introduced. On this basis, the latest research results under the technical requirements of single parameter and multi parameter at home and abroad are listed, and the single parameter distributed optical fiber sensor and multi parameter quasi distributed optical fiber sensor are compared and analyzed in improving the light source, optical fiber structure and demodulation technology. Finally, the future development trend is prospected.

The combination of nano-film and optical fiber provides various potentials for novel sensing. In order to analyze the formula design of the temperature-sensitive film and its influence on the sensing characteristics of the optical fiber temperature sensor. According to the theory of optical thin film and the temperature sensing principle of optical fiber sensor, the formla design of the sensitive thin film in the optical fiber temperature sensor is discussed, and the temperature sensing characteristic model of the thin film optical fiber sensor is constructed. Based on the parameters and performance of the test system and its requirements for the interference spectrum, a Fabry-Perot film cavity with good symmetry is designed. By comparing the sensing characteristics of Fabry-Perot formula with different film thicknesses, a formula is selected. The influence weights of the thermo-optic coefficient and thermal expansion coefficient of the high and low refractive index film materials on the temperature sensing characteristics are analyzed, which provides theoretical basis for the plating and process formulation of the temperature sensor sensitive thin film.

In order to realize high-sensitivity optical fiber temperature sensing, a multi-wavelength erbium-doped optical fiber temperature sensor with double Brillouin frequency shift interval is proposed and verified. In the experiment of this scheme, the laser output with a wavelength of 1558.214 nm is used as the Brillouin pump, which is amplified by the erbium-doped fiber amplifier, then passes through a double frequency cavity composed of two three-port circulators and a section of 20 km single-mode fiber, which is both the Brillouin gain medium and the temperature sensing element. The experimental results show that the temperature sensing coefficient can be adjusted from 2.186~15.328 MHz/℃ under seven stable double frequencies with high signal-to-noise ratio, and the temperature measurement error of the highest Stokes wave is ±0.322 ℃.

Wavelength crosstalk problem occurs when there are too much multiplexing in fiber Bragg gratings or the limited bandwidth, and the performance of signal demodulation method is related to the accuracy of result. In this paper, a novel central wavelength demodulation method based on meta-heuristic algorithm is proposed, the least-squares function of the discrepancy between the actual spectrum and the theoretical spectrum is employed as the optimization objective, the marine predators algorithm with excellent exploitation and exploration capabilities is developed to solve the problem. Numerical simulation and experiment verify that the proposed algorithm is an effective and feasible wavelength demodulation method, which can realize the recognition of multi-spectral overlap and ensure the demodulation accuracy.

In order to realize the intelligent control and self-adaptation of product installation, an intelligent detection and correction system based on optical fiber sensing network is proposed. The optical fiber sensing network is used to reconstruct the stress field distribution of the tooling, calculate the functional relationship between the wavelength offset and the position offset, and quantify the corresponding relationship between the sensing network and the position correction data. Finally, it provides intelligent detection and correction parameters for the automatic installation system. The experiment uses a common plug-in installation structure to test and analyze the stress change in the range of 0~200 N. The experiment results show that the system has an obvious response law to the position deviation caused by the stress change. The relative error between the inversion accuracy and the standard accuracy is better than 10.0%. It has good stability.

In order to analyze the impact of the earthquake on the transmission line, the seismic case data is collected by the optical power grounded waveguide(OPGW) distributed optical sensor monitoring system, analyzes the characteristics of the vibration of the transmission line affected by the earthquake, and a preliminary attempt is made to evaluate the impact of earthquake on transmission lines based on the measured vibration data of the tower line system, which fully verifies the optical sensor monitoring system based on the OPGW can accurately monitor the seismic activity of the transmission line channel, and can sense the impact of the seismic wave on the entire line.

In order to effectively extract Brillouin frequency shift of Brillouin distributed optical fiber sensing system and reduce data processing time, an edge feature extraction method of Brillouin scattering spectral image based on second-order Laplacian edge detection operator is proposed. The Brillouin frequency shift is regarded as the edge of the scattering spectral image, and the second-order Laplacian edge detection operator is used to sharpen the Brillouin scattering spectral image, the binary image is obtained by non maximum suppression and adaptive threshold to remove the invalid edge, and the Brillouin optical time domain reflection temperature sensing system is built. The experimental results show that the method can accurately extract the frequency shift feature, and the processing time is far less than that by using curve fitting method, which are conducive to shorten the temperature measurement time of the system.

In order to improve the phase noise tracking performance of coherent fiber communication system, a phase noise tracking algorithm——modified decision-directed recursive least square(DD-RLS) algorithm has been proposed. The modified DD-RLS algorithm and nonlinear pre-compensation algorithm are combined to suppress cross-phase modulation(XPM) in WDM coherent fiber system. Transmission simulation shows that the algorithm can effectively suppress the XPM effect in the system, it can track the nonlinear phase noise in coherent wavelength division multiplexing(WDM) optical fiber communication systems more efficiently than the traditional DD-RLS algorithm, and can improve the Q2 factor of the signal by 0.8 dB comparing with the traditional algorithm in a 1000 km transmission simulation with 11 channels.

In order to further reduce radio-over-fiber system cost and improve transmission performance, a novel optical carrier reuse mothed based on amplitude modulation in both uplink and downlink is proposed. The principle of the method is introduced, and its feasibility is verified by Optisystem software. The simulation results show that the performance of the system is optimal when the "0" code amplitude of the downlink transmission data is 1.4 V, the beam splittr's spectral ratio is 5∶5, and the modulator's extinction ratio is 5.2 dB.

Aiming at the complicated and changeable channel of seawater laser communication channel, Monte Carlo simulation is used to simulate the transmission process of blue green laser in seawater channel, and the simultaneous interpreting of the received power under different transmission distances is obtained. The Gauss function and arc fitting algorithm are used to fit the statistical results respectively. The Gauss fitting error and the arc fitting error of the laser in different distances are calculated. The fitting error of the arc algorithm is less than that of Gauss function fitting. Based on the arc fitting algorithm, the underwater wireless optical communication channel model is established. According to the transmission model, the relationship among laser transmission distance, arbitrary receiving position and receiving power can be quickly obtained under certain sea water quality parameters, which provides reference value for the design of underwater wireless optical communication system.

In order to study the strain performance of optical fiber composite overhead ground wire(OPGW) in long-term operation, Brillouin optical time domain analysis(BOTDA) is used to monitor the strain of new cables and old cables in different icing environments, and the Brillouin frequency of fiber in OPGW cables in long-term external environment is compared and analyzed. The test results show that the operation time and icing level are the main factors affecting the strain performance of fiber in OPGW cables.

The polarization of optical signal in optical fiber composite overhead ground wires(OPGW) will change due to wind vibration, which leads to the degradation of the system performance. In order to understand the effect of wind vibration on the polarization state in OPGW, and polarization state of OPGW changes under different swing conditions are simulated by experiments. Based on the measured data, the paper analyzes the rule of the polarization state change and concludes how it influences the coherent optical communication system, and gives the calculation basis for compensation algorithm in coherent optical communication system. The experimental results show that the rotation speed of signal polarization caused by the two kinds of wind vibration is 700 rad/s and 7 krad/s respectively, and the receiver needs to compensate for this magnitude velocity of the polarization state change.