Comprehensive demonstration of link fiber-induced spurious signals in interferometric FBG hydrophones

The interferometric Fiber Bragg Grating (FBG) hydrophone has wide applications in ocean acoustic detection and seismic wave monitoring. The interference signal from external sources is routed to the elements through the link fiber connecting the dry and wet ends, which is a critical bottleneck that limits system performance. This paper presents a comprehensive model for link fiber-induced spurious signals, which demonstrates the physical processes and signal characteristics of the Doppler effect and the Rayleigh scattering effect, illustrating how they interact to generate the link interference signal. It is found that the dominant physical mechanism depends on the location of the link interference signal source. The interference signal source closer to the dry end mainly transmits signals to hydrophone elements through the Doppler effect, and the amplitude of the induced spurious signal depends on the frequency. When the link fiber is longer, the interference signal from the source near the wet end is simultaneously transmitted to hydrophone elements through the Doppler effect and Rayleigh scattering effect, during which the Rayleigh scattering effect leads to a spurious signal intensity increase of up to 10 dB. Additionally, the correlation with signal frequency decreases as instability rises. This thorough analysis of the physical process of link fiber-induced spurious signals will advance the development of interference suppression techniques, substantially boosting the sensitivity and reliability of interferometric FBG hydrophones for applications in harsh environments with disturbances.