Photonics-based wideband Doppler frequency shift measurement by in-phase and quadrature detection

The authors propose and demonstrate a photonics-based wideband Doppler frequency shift (DFS) measurement scheme through in-phase and quadrature detection. The system has a compact structure applying cascaded phase modulation and polarisation modulation. It is easy to implement since both the value and sign of the DFS can be estimated by simple signal processing. More importantly, the proposed scheme is suitable for both DFS measurement and direction discrimination over a very wide frequency range. In the experiment, accurate DFS measurement with a large carrier frequency range from 5 to 40 GHz is demonstrated with the measurement error kept within +/- 12 Hz.