Underwater Acoustic Pressure Sensing using Optical Fiber Bragg Grating

A large amount of untapped resources lies underwater, which covers almost 70% of the surface of the earth. Therefore, there is a need to monitor the underwater behavior and operations occurring inside seawater by developing a robust and mature technology. Acoustic signals are capable of long-range detection with significantly less latency (due to underwater speed of sound). This paper presents the designing and simulation of an Optical Fiber Bragg Grating (OFBG) sensor. OFBG has properties such as immunity to electromagnetic interference, remote sensing, stability in harsh environments. OFBG sensors are in use in an environment where conventional sensors are unsuitable because of the capabilities such as multiplexing, high sensitivity, and wide dynamic range. Mostly the OFBG sensor is in use to measure pressure, stress, and strain change by observing a shift in Bragg's wavelength caused by natural calamity, presence of a variety of aquatic creatures, and anti-submarine movements. GratingMOD design tool is in use for analyzing and synthesizing complicated grating profiles. During the simulation, the highest-pressure variation considered is 39.81 MPa (undersea earthquake) to lowest 0.56KPa (Right Whale) to observe strain and stress on the sensor. The underwater activity created stress/strain resulting in Bragg's wavelength shift towards the Direction of Arrival (DOA) of the acoustic signal. The recorded wavelength change for Undersea Earthquake is 1560.86241(nm), Right Whale is 1550.000153(nm).