Sensitivity of an Opto-Acoustic Detector Based on a Modalmetric Interferometer with the Length of Interacting Fibre

This paper describes a simple opto-acoustic detector based on a fibre-optic modalmetric device in reflective structure, primarily thought for digital acoustic communication. A single-mode fibre was spliced with a sensitive multimode fibre (s-MMF) strand leading to a modalmetric device, which was probed with 1550 nm wavelength. A non-linear increase of the phase shift and a higher effective sensitivity of the device were observed when the length of the s-MMF in contact with the surface receiving acoustic signals was increased from 5 to 25 cm, demonstrating enhanced phase sensitivity due multimode interference and the antenna gain.