Ellipse Fitting Demodulation System of Fiber Optical Hydrophones System Based on 3×3 Coupler
Ruixuan Qu, Duanming Li, Jiangfei Hu, Minxue Gu · 2020
3×3 coupling demodulation has the advantages of no carrier modulation, simple structure and capacity of realizing all-optical fiber hydrophone system. However, the asymmetry of 3×3 coupler will introduce demodulation errors to the usual 3×3 demodulation scheme, and the demodulation scheme using three channels of the 3×3 coupler is not conducive to the formation of large-scaled time division multiplexing system. In view of the above defects, this paper uses the ellipse parameter fitting combined with the digital arctangent algorithm to demodulate signals of two channels of the 3×3 coupler. The principle of this demodulation method is demonstrated in this paper, and simulations to verify the feasibility of the algorithm is carried out. Based on the simulation, the demodulation system in the laboratory was built. The sinusoidal analog signal with amplitude of 4.25v at 1000Hz was demodulated. The demodulation amplitude was 4.2024rad, and the harmonic suppression ratio THD of the demodulated signal frequency spectrum was 39.2014dB. The linear correlation coefficient of demodulated signals with different amplitude at 1000Hz was 0.98. The average demodulation phase difference of 3×3 coupler was 118.8877 °, and the standard deviation was 1.4616 °. Experiments showed that the demodulation system had good consistency and accuracy.