355 nm optical frequency discriminator and closed-loop control system for spaceborne wind lidar

The three-channel 355 nm optical frequency discriminator is widely used in the frequency discrimination of the backscattered signal of the space-borne wind lidar, which is the core component to discriminate the wind speed Doppler frequency shift in the double-edge method, and its parameters and reliabilities determine the detection accuracy of the system. A 355 nm three-channel etalon module based on piezoelectric transducer (PZT) crystal tuning was developed, with the effective diameter of 35 mm, the peak transmittance of 75%, the free spectral range of 12.5 GHz, and the full width at half maximum of 1.7 GHz. Through the three-channel test system, the parameters including free spectral range, full width at half maximum, peak transmittance, and tuning coefficient were tested. The test results show that when the external driving voltage is 75 V, the peak transmittances of the three channels are 0.859, 0.878, and 0.735, respectively. The full width at half maximum is 1.843 GHz, 1.882 GHz, and 1.611 GHz, respectively. The tuning coefficients are 1.96 GHz/V, 1.93 GHz/V, 1.88 GHz/V, respectively. In view of the inconsistent tuning coefficients of three channels of the PZT crystal of the optical frequency discrimination module, the influence range of the analysis on the wind speed error is ±0.1m/s. Through the test of the closed-loop control system, the system can realize the real-time locking of the 355 nm laser emission frequency, solve the problems caused by the inconsistent initial position of the optical frequency discrimination module in each working state, improve the frequency discrimination of wind speed, and can achieve the stable locking time of more than 30 minutes, which meets the application requirements of space-borne wind lidar. Simulation studies show that when the interval of three-channel optical frequency discrimination module changes by 0.08 nm, the resulting wind speed error is 1 m/s.