Intensity Compensation of Echo Pulses for Fiber Interferometers Based on uwFBG Reflectors

We report on current theoretical and experimental results of echo pulses based on ultra-weak Fiber Bragg Gratings (uwFBGs), using intensity compensation to solve the signal distortion caused by light pulse delay. Cubic Spline Interpolation is applied, leading to better robustness for the interference intensity. Then the linear compensation value is obtained by comparing the peak intensity in order to correct attenuation in three-way optical path. We report improvements over the conventional demodulation algorithm based on 3×3 coupler with circulator. The experimental results have shown that, when the intensity reduction is existed due to pulse delay, the hydroacoustic field could be reconstructed with high fidelity by using the proposed method. Leading to much lower noise density level for the interference pulse intensity, more than 7 dB when the reference signal is 1rad/√Hz in 5~50 Hz, and the SNR is improved approximately 10 dB@10 Hz. The proposed method exhibits a particularly applicability in passive optical path, which is of great importance for increasing the practicality of the system in complicated environments.