Parameters optimization of an optical doppler radar system for velocity measurement

Couplers in the fibre optical system of laser Doppler speedometer have great impact on its performance. In order to maximize the system's signal- to-noise ratio (SNR), the relationship between the input optical power and the output voltage of the photoelectric detector is measured and its response function is obtained based on the method of polynomial fitting. The impact of the nonlinear response of detector on the laser Doppler speedometer is analysed and the preferable local oscillator (LO) power is chosen to alleviate the nonlinear response. The optimum parameters of the designed laser Doppler speedometer are derived according to the relationship between the SNR and the splitting ratio of two principal couplers. It is found in the system that when the direct splitting ratios of the two couplers satisfy the condition C₁ = C₂ = P₀/P_1as the SNR of the whole system gets its maximum value.