An eye-safe coherent lidar for speed measurement

An eye-safe, coherent Doppler Light Detection and Ranging (CDL) system for speed measurement under development at BUAA's School of Instrument Science and Opto-electronics Engineering is introduced in this paper. It consists of a 1.55-μm Er-doped fiber laser transmitter, a monostatic optical antenna, a single-mode fiber (SMF) interferometer, an InGaAs photodiode detector, and signal processing equipments. All devices of optical circuit are connected by SMFs making the system reliable and setup arrangement flexible. The goal is to give the evaluations of the Doppler frequency shift and platform speed. Since the speed accuracy is time-independent, the CDL system can be used for integrated navigation system. The quality of Doppler-shift estimation by a spectrum analysis technique, fast Fourier transform (FFT) algorithms, ameliorates as the signal-to-noise ratio (SNR) increases. For the developed CDL system incorporating with SMF interferometer, only the light beam of mode LP₀₁ is permitted to propagate, therefore the SNR is improved greatly. Experiments were performed on a moving hard target with the CDL system and the results were presented.