SNR enhancement of fiber Bragg grating array-based φ-OTDR using pulse coding

Phase Sensitive Optical Time Domain Reflector (φ-OTDR) is widely used due to its characteristics of distributed sensing, high sensitivity, quantitative measurement and fast dynamic response. However, as the sensing distance of the system increases, the reflected optical power of the system decreases gradually, resulting in a decrease in the signal-to-noise ratio of the demodulated signal. In this paper, a Fiber Bragg Grating (FBG) array is used as the sensor, and a fiber Bragg grating array-based φ-OTDR coding system is proposed to eliminate the interference fading of the fiber optic φ-OTDR coding system and improve the signal-to-noise ratio of the system. First, we deduce the codec theory based on fiber Bragg grating φ-OTDR. Then, in the verification experiment, the 32-bit Golay code was used to achieve a signal-to-noise ratio of 33.7 dB at the end of the fiber Bragg grating array with an interval of 15 m and a length of 1 km, which was 6.2 dB higher than that of the single-pulse system.