Microwave Photonic Mixing Approach to Doppler Frequency Shift Measurement

A microwave photonic mixing approach to laser Doppler frequency shift (DFS) measurement employed for high-velocity estimation is proposed. Based on optical carrier-based microwave interferometry, the DFS of the light wave frequency domain is mapped to the microwave frequency domain. With a modulated broadband light wave, a sufficiently small coherence length of a light wave is produced, avoiding the influence of optical interference on photonic mixing. Compared to conventional laser DFS measurement, the frequency of intermediate frequency (IF) signal can be reduced by 4 and 5 orders of magnitude. Microwave photonic mixing based on a heterodyne interferometer is also performed to eliminate the direction ambiguity of motion. In a proof-of-concept experiment, the frequency shifts from 0 to 100 kHz with a frequency shift error of