Wideband Doppler frequency shift measurement and direction discrimination based on optical single sideband modulation with a fixed low-frequency reference signal

A wideband Doppler frequency shift (DFS) measurement and direction discrimination method based on optical single sideband (OSSB) modulation with a fixed low-frequency reference signal is proposed and experimentally demonstrated. In the proposed approach, the transmitted signal and the fixed low-frequency reference signal are applied to the lower and upper Mach–Zehnder modulators (MZMs) of a dual-drive dual-parallel MZM (DD-DPMZM) respectively, for realizing OSSB modulation independently. The echo signal is applied to a conventional MZM for optical double sideband (ODSB) modulation. A low-speed photodetector (PD) is used to implement optical-to-electrical conversion and generate three low-frequency beating signals. Both the value and direction of the DFS can be simply obtained by analyzing the frequencies of the three low-frequency beating signals. The proposed scheme has a simple structure, a wideband operating frequency range, and a low requirement of the receiving circuit. Experiments demonstrate that wideband DFS measurement and direction discrimination within 5∼18 GHz with a measurement error of less than ±0.06 Hz are achieved by using a 20 MHz reference signal.