Fig. 1. Demodulation of heterodyne algorithm

Fig. 2. Block diagram of acousto-optic modulator

Fig. 3. Effect of differential carrier frequency offset and amplitude jitter on demodulation noise. (a) Effect of differential carrier frequency offset Δf'; (b) effect of carrier amplitude jitter ΔM'

Fig. 4. Schematic of optical path for generating differential frequency dual-pulse light based on MZI structure full polarization maintaining optical path and parallel AOM

Fig. 5. Schematic of optical path for generating differential frequency dual-pulse light based on MI structure non-polarization-maintaining optical path and serial AOM

Fig. 6. MI optical path design and packaging. (a) Comparison of volume between MI optical path packaging and AOM (driver and acousto-optic crystal); (b) MI vacuum pumping and vibration isolation packaging

Fig. 7. Experiment setup based on MI and serial AOM heterodyne demodulation algorithm

Fig. 8. RF signal and optical pulse signal generated by heterodyne optical path. (a) RF driving frequency of serial AOM; (b) dual-pulse light output by MI; (c) matching interference signals output by fiber optic hydrophones

Fig. 9. Actual RF driving signals of AOM 1 and AOM 2 captured by oscilloscope

Fig. 10. Demodulation results before and after improvement of the optical path for differential frequency generation. (a) Demodulated noise time-domain spectrum of MZI with parallel acousto-optic modulation; (b) demodulated noise time-domain spectrum of MI with serial acousto-optic modulation; (c) frequency-domain spectra of demodulated noise

Fig. 11. Noise fluctuations at three frequency points (10 Hz, 100 Hz, 1000 Hz) over an 8-hour period