A four-element hydrophone array system using a fiber Bragg grating laser system is described. The demodulation technique for the array combines a 3\times 3 coupler-based interferometer and three wavelength division multiplexers (WDMs). It is believed to be a new passive approach to use a WDM and a unique arithmetic method. The operational frequency limit depends only on the frequency of its electronic portion. The designed system has achieved a minimum of \sim 7.2\times {10}^{-7}\text{pm}/\sqrt{\text{Hz}} detectable wavelength perturbation for frequencies that are greater than 200\text{\hspace{0.17em} Hz} .