6–40 GHz photonic microwave Doppler frequency shift measurement based on polarization multiplexing modulation and I/Q balanced detection

A novel optical approach to implement broadband Doppler frequency shift (DFS) measurement is proposed and demonstrated. Through I/Q balanced detection using a polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) and two balanced photodetectors, the concerned microwave DFS is estimated with clear direction discrimination and a significant improved resolution. In the experiments, the DFSs from -100 to 100 kHz in 20-kHz step are successfully measured and estimated for microwave signals with the operating frequency from 6 to 40 GHz. The error of measuring is calculated to be less than 8 Hz. The approach is uncomplicated and manageable to implement, which provides an alternative solution for future wideband electronic systems such as Doppler radar, satellite communications or electronic countermeasures.