Long Period Grating-based optical fibre sensor for the underwater detection of acoustic waves

In this work, a Long Period Grating (LPG)-based acoustic sensor was designed and evaluated for underwater acoustic pressure measurement. The paper presents the sensing principle and characterization of the device, prior to discussing the results of a series of experiments carried out. The optical sensor was based on a LPG clamped, placed underwater and exposed to acoustic waves generated by an underwater loudspeaker. Its characteristics were measured by varying either the amplitude, the frequency of the acoustic waves, or the distance between the sensor and the acoustic source and the depth of the sensor in the water. The LPG-based sensor was subsequently fully characterized and the results obtained are cross-compared with data obtained from acoustic sensing measurements in air.