The effects of scaling and bends in a fiber‐optic modalmetric acoustic detector

Abstract

This report describes a simple and very sensitive modal interferometer (modalmetric) opto-acoustic detector primarily thought for digital acoustic communications. The modalmetric device was made from a single-mode fiber spliced with a sensitive multimode fiber (s-MMF) strand. A nonlinear increase of the phase-shift and a higher effective sensitivity of the device were observed when the interaction length of the s-MMF in contact with the surface receiving acoustic signals was increased from 5 to 25 cm and also when the s-MMF was bent-scaling and bend effects. A sensitivity increase of 14.2 dB was measured for very weak acoustic signals caused by at least three interfering modes. All tests in the proof-of-principle basis were performed at 42.9 kHz carrier frequency and 1550 nm wavelength.