Unambiguous DFS Measurement System Based on an Integrated Photonic Chip With Wavelength-Selective Modulation

This paper presents and experimentally demonstrates a Doppler frequency shift (DFS) measurement system based on on-chip coherent wavelength-selective modulation, fabricated on a lithium niobate on insulator platform. The device employs a Mach-Zehnder interferometer like structure with parallel arms, each consisting of a cascaded micro-ring resonator and phase modulator. By independently modulating the transmitted and echo signals on different wavelengths, the DFS is determined from the beat frequency generated between their corresponding sidebands. This methodology exhibits inherent robustness against both power fluctuations and wavelength-selection imperfections. Experimental characterization using 12 GHz, 15 GHz and 18GHz signals demonstrated a maximum measurement error within ±0.6 Hz over a DFS range of ±100 kHz. Simulation results further confirm the system's ability to distinguish between multiple moving targets with identical speeds but opposing directions.