Research on 3×3 coupler photoelectric detecting technology based on light source modulation in fiber optic hydrophone

The photoelectric detecting technology bas-ed on the 3×3 coupler is widely used in interferometric fiber optic hydrophone systems. Parameters such as DC and AC amplitude and phase difference of the couplers have a crucial influence on the accuracy and stability of demodulation. In this paper, an ellipse fitting algorithm based on light source modulation is used to achieve real-time, accurate measurement and correction of the detection parameters, eliminating the impact of the 3×3 coupler asymmetry on the system. The signal detecting accuracy is improved with the effectively suppressed system noise, realizing the stable signal detecting for the fiber optic hydrophone. Compared with the traditional ellipse fitting algorithm based on external large signal modulation, the proposed algorithm presents higher reliability and practicability. Furthermore, in view of the characteristics of large-scale array data processing and high real-time requirements, this paper adopts a heterogeneous design of ARM+FPGA, using the SDSoc platform to carry out software and hardware collaborative development of the 3×3 coupling demodulation algorithm based on light source modulation. ARM implements task allocation and scheduling functions, and FPGA implements specific function calculation modules. this design greatly reduces the pressure of computer data processing, and ensures that the optical fiber hydrophone system can complete automatic parameter calibration while real-time demodulation. The demodulation efficiency of the 3×3 algorithm is improved, coupled with the high integration and easy expansion of the system itself, provides the possibility for future large-scale arrays of 3×3 detection schemes in fiber optic hydrophone systems.