Research On Characteristics Of Fiber Bragg Grating And Application In Raman Lidar

Fiber Bragg grating has become one of the most important optical fiber devices in the information field. Due to its inherent anti-electromagnetic interference and excellent spectral characteristics, the near-infrared fiber Bragg grating has been widely used in the field of communication and sensing. Based on the characteristics of near-infrared Bragg gratings, the advantages of ultra-multi-point multiplexing in sensing field are simulated and experimentally studied in this paper. Combined with the realistic needs of laser remote sensing in our research team, the application research of visible-band fiber Bragg grating technology in the field of lidar has been carried out, which may promot the development of spectroscopic techniques for the space-based or onboard of lidar.To solve the problem of the number of fiber Bragg grating sensing nodes, the ultra-multi-point time-division multiplexing low-reflectivity fiber grating sensing network is studied. The system utlizes the fiber-distributed feedback narrow line-width laser as the light source, and realize the nanosecond-scale pulse laser driver which may output the driving signal with pulse width of 5 ns. The nanosecond-scale response broadband signal amplification and conditioning circuit is designed using the peak-hold circuit of voltage comparator as the core,to realize the low-speed high-reliability acquisition of peak signal with the pulse width of 5 ns and rise time of 2.2 ns. The results show that the system with the same low reflectivity fiber Bragg grating in series structure has the spatial resolution of 43 cm, the settling time of about 15 ns, the linear correlation of 0.9992, the linearity of better than 2 %, and the measurement error of about 4 %, The feasibility of time-division multiplexing fiber Bragg grating sensing network with high temporal-spatial resolution strain sensing is verified.In order to lessen current complexity problem of the demodulation for time division multiplexing fiber Bragg grating sensor network, a edge demodulation technique with fiber grating spectrum and correction method are proposed on the basis of the spectrum scanning light source and the edge demodulation with broad spectrum light source. To broaden the range of fiber grating edge demodulation,a dual-source alternation excitation mode is proposed to improve the measurement stability and sensing precision. Simulation and experiment results show that the sensitivity of fiber Bragg grating strain to its applied stress is appoxmately 0.0497 ?? / N, that the maximum error of single measurement is 18 ??, that the nonlinear error is 2.8% and that the relative error of the measured mean value is 2 %.Due to the limits of complex adjustment and low stability of spectroscopic system, the Raman lidar is not suitable for space-based or on board applications. Combined with the excellent spectral characteristics of fiber Bragg gratings, a Raman temperature measurement lidar system based on fiber gratings is constructed. Using coupled-mode theory and transfer matrix model, the existing optical fiber grating technique is extended to the visible light band.Based on the spatial spectral characteristics of blazed grating, an absolute temperature measurement Raman lidar system is designed, and then the parameters of visible light band fiber gratings are optimized and analyzed. The simulation results validate the feasibility of the designed Raman spectroscopy system and the inversion algorithm, and provide a new detection and a correction method for high precision laser remote sensing of atmospheric temperature.To adapt to the miniaturization of rotational Raman spectroscopy system, an all-fiber rotational Raman spectroscopy system is proposed. To improve the low signal-to-noise ratio caused by single spectral line extraction and to meet the reqirement of all-day detection with high-precision, a multi-stage cascade spectroscopic system is proposed based on sampling fiber Bragg grating. Then the main factors (refractive index modulation depth, total grating length, sampling period and duty cycle) influencing the out-of-band inhibition rate of sampling fiber Bragg grating are analyzed. Finally the optimal out-of-band inhibition rate of sampling fiber Bragg gratings is obtained by optimization. The simulation results showed that the system can detect up to a maximum height of 1.6 km in daylight and a height of 2.6 km at night.Theoretical research and experimental results show that the fiber Bragg grating has excellent spectral characteristics and multiplexing properties, which can be used in the field of lidar remote sensing by extending to the visible light band. Its advantages such as miniaturization, anti-interference and easy compatibility bring a new solution for space-based Raman temperature measurement lidar.