Demodulation of a Hydroacoustic Sensor Array of Fiber Interferometers Based on Ultra-Weak Fiber Bragg Grating Reflectors Using a Self-Referencing Signal

Abstract

We report on current theoretical and experimental results of hydroacoustic sensing array based on ultra-weak fiber Bragg gratings, using a modified phase generated carrier (PGC) demodulation method with a self-referencing signal. The self-referencing signal is obtained by a sensor isolated from acoustic signals and other environmental disturbances. We report improvements over the conventional PGC methods. Using our demodulation method and with nonsensitized bare fiber (reference sensor <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) keeping separate from water, experiment testing demonstrates a minimum detectable hydroacoustic pressure of 2239 μPa/√Hz. The properties of our demodulation method are also compared with those of the conventional PGC algorithms. Both simulation and experiments indicate that our demodulation method is immune to the drifts of modulation depth <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> and of carrier frequency, and the detectable frequency range can be increased by five times compared to using conventional PGC methods with the same carrier frequency. The sensor array exhibits a particularly large response in the very low frequency region, which is of great importance for underwater seismic detection and submarine applications.