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In response to the problem of common mode noise in transmission optical cables caused by external environmental factors during the long-term operation of underwater autonomous fiber optic hydrophone systems. This paper proposes a single-element fiber optic hydrophone based on a symmetrical structure for common mode noise suppression. The proposed symmetrical structure utilizes the characteristics of fiber optic couplers, where the output phase difference of the two interference lights is fixed, and then the two interference lights are output separately through an optical circulator. Subsequently, the detected two interference signals are used to noise cancellation processing, followed by phase demodulation, in order to suppress common mode noise and improve detection performance. A corresponding testing system was built, and the experimental results indicate that this measurement system has a simple optical circuit and does not require additional optical paths and time division channels compared with traditional structures. In addition, this measurement system can effectively reduce common mode noise. The actual test results of common mode intensity noise suppression are in good agreement with theoretical results. The symmetric system structure and common mode noise suppression method and theories reported in this article can also be extended to other interference systems, and hence have important value for large-scale multiplexing of hydrophone arrays.
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