Acoustic sensor based on fiber-optic polymeric resonator

Abstract

Acoustic measurements are the obvious target of acoustic investigations in this paper, using an opto-mechanical frequency analyzer. This proposed sensor is designed using micro-optical dielectric sensors based on whispering gallery modes (WGMs). This phenomenon, commonly referred to as WGM, is excited by evanescently coupling light from a tunable laser diode using a tapered single-mode optical fiber. A measurement arrangement can typically be separated into source and receiver components. The receiver component consists of a sound level meter or sound analyzer that we call an opto-mechanical frequency analyzer, which displays the total sound level in frequency-dependent data. It can also produce results such as spectra or impulse responses. Furthermore, measurements are based on special measurement environments that allow several reference sound fields to be created. The proposed design is composed of a tuner that consists of slots with different geometries with dielectric beams placed on each one. These beams are made from polydimethylsiloxane. The spherical optical polymeric resonators are mechanically coupled to the dielectric beams placed at each slot. The tuner has a different resonant frequency at each slot, which depends on the effective length of the beam. Sound waves deform the polymeric cavity, causing a shift in its transmission spectrum. A technique based on signal cross-correlation is used to calculate that shift, which is known as WGM shift. An analysis and calibration are carried out along with preliminary designs and experiments. Results prove that the proposed technique can be used as a very high-resolution frequency analyzer due to the high quality factor (Q-factor) of the resonators, which is 106 compared to the typical electrical frequency analyzer that has a Q-factor up to 102. Similar to an optical prism, this device can be used to split sound into its constituent frequencies.