On-chip Photonic Method for Doppler Frequency Shift Measurement

Photonic Doppler frequency shift (DFS) measurement based on an integrated silicon photonic chip, which contains two cascaded dual-drive-Mach-Zehnder modulators (DDMZMs) and a photodetector (PD), is proposed and experimentally demonstrated. The reference signal is applied to the first DDMZM, while the transmission signal and the echo signal are injected into the second DDMZM through a differential RF probe. The optical carrier modulated by the three microwave signals is sent to a PD to achieve optical-to-electrical conversion. The DFS generated by the frequency beating between the transmission signal and echo signal, and two additional frequency components produced by the frequency beating between the transmission/echo signal and the reference signal are obtained. The target moving direction can thereby be identified by comparing the frequency locations of these three beat signals. A proof-of-concept experiment is carried out. The DFS from -100 to 100 kHz is estimated for a microwave signal at 10 GHz with an error of less than 1 Hz.