Photonic approach to wideband Doppler frequency shift estimation system based on a DPMZM and a Sagnac loop

Abstract

A photonic approach to wideband Doppler frequency shift (DFS) measurement and direction discrimination is proposed and demonstrated. In the proposed scheme, a dual-parallel Mach-Zehnder modulator is used to generate carrier suppressed double sidebands signals, which are orthogonally polarized in a Sagnac loop incorporating a fiber Bragg grating. The DFS is transformed into a low-frequency electrical signal. The value of the DFS is obtained by analyzing the spectrum of the output current. The orientation of the DFS is estimated by a 90° hybrid coupler. The entire DFS measuring process is independent of the radar carrier frequency and suitable for wideband spectrum measurement range. Simulations are performed to verify the proposed scheme, the value and the orientation of the DFS can be estimated simultaneously. As the target moves toward the radar or moves away from the radar, there are, respectively, 36.8 dB and 39.1 dB power difference between the two branches of the hybrid coupler. In addition, the performance of the proposed approach in term of the signal-to-noise ratio and stability are discussed.