Expansion of Dynamic Range in Interferometric Fiber Optic Hydrophone

In a conventional interferometric fiber optic hydrophone where a light pulse stops being generated before the last pulse finishes passing through a sensing fiber, the dynamic range cannot be expanded even if the sensing fiber is made long to enhance sensitivity. The reason is that a long repetition period of the light pulse causes a failure in demodulation of a high-level signal with a quick phase change. In this paper, the dynamic range is expanded at least by 26 dB by shortening the repetition period such that the pulses interfering with each other are avoided. The effect of a wide dynamic range is also confirmed by observing that when a high-level sound simulating a jamming sound is applied, a sound 95 dB lower than the jamming sound can be detected with the newly developed hydrophone.