Optimization design of the tuning method for FBG spectroscopy based on the numerical analysis of all-fiber Raman temperature lidar

All fiber Raman temperature lidar for space borne platform has been proposed for profiling of the temperature with high accuracy. Fiber Bragg grating (FBG) is proposed as the spectroscopic system of Raman lidar because of good wavelength selectivity, high spectral resolution and high out-of-band rejection rate. Two sets of FBGs at visible wavelength 532 nm as Raman spectroscopy system are designed for extracting the rotational Raman spectra of atmospheric molecules, which intensities depend on the atmospheric temperature. The optimization design of the tuning method of an all-fiber rotational Raman spectroscopy system is analyzed and tested for estimating the potential temperature inversion error caused by the instability of FBG. The cantilever structure with temperature control device is designed to realize the tuning and stabilization of the central wavelengths of FBGs. According to numerical calculation of FBG and finite element analysis of the cantilever structure, the center wavelength offset of FBG is 11.03 nm/°C with the temperature change in the spectroscopy system. By experimental observation, the center wavelength offset of surface-bonded FBG is 9.80 nm/°C with temperature changing when subjected to certain strain for the high quantum number channel, while 10.01 nm/°C for the low quantum number channel. The tunable wavelength range of FBG is from 528.707 nm to 529.014 nm for the high quantum number channel and from 530.226 nm to 530.547 nm for the low quantum number channel. The temperature control accuracy of the FBG spectroscopy system is up to 0.03 °C, the corresponding potential atmospheric temperature inversion error is 0.04 K based on the numerical analysis of all-fiber Raman temperature lidar. The fine tuning and stabilization of the FBG wavelength realize the elaborate spectroscope of Raman lidar system. The conclusion is of great significance for the application of FBG spectroscopy system for space-borne platform Raman lidar.