A high signal-to-noise ratio balanced detector system for 2 μm coherent wind lidar.

A balanced detector system with a high signal-to-noise ratio (SNR) is the key technology for 2 μm coherent wind lidar, which can enhance the ability for the digital receiver to detect extremely weak signals. The photodiode is the main detection component of a balanced detector system. The variance of junction capacitance of different photodiodes will cause the degradation of SNR. Based on the linear relationship between the junction capacitance of a photodiode and the reverse voltage in the double logarithmic coordinates, a balanced detector system is designed to have the ability to adjust the reverse voltage by using the external digital-to-analog converter. An optimization of the circuit performance can be achieved by adjusting the junction capacitance, which significantly affects the circuit noise and signal bandwidth in the design of the high bandwidth transimpedance amplifier, which is sensitive to parasitic capacitance and component error. A simplified optical system is built to test the performance of the designed balanced detector system. The results show that the SNR of the detector system is ∼10% higher than that of the commercial product, which can further increase the detection distance of the wind lidar by ∼1.5 km for the detection limit of 10 km.