S-shaped microfiber based diaphragm supported optical microphone

Abstract We propose and demonstrate a simple and highly sensitive optical microphone based on S-shaped tapered fibre (STF). The short pigtailed end of the STF is attached to the centre of a thin circular nitrile diaphragm. The applied acoustic signal deforms the nitrile diaphragm and due to the affixation, the STF structure gets modified leading to change in the bending angles of the two STF bends. As a consequence, the photodetector output, detecting the reflected light intensity of the STF, varies in accordance with the applied acoustic signal. Various properties of the proposed sensing setup can be easily tailored by changing the diaphragm diameter and thickness, and the shapes and size of the STF. For an optimized configuration, the proposed sensor achieves a sensitivity of 3.07 mV Pa−1 and a minimum detectable pressure of 36.48 mPa Hz−1. The sensor shows a linear behaviour up to 1300 Hz and the experimental value of its first order natural frequency is 1455 Hz.