Investigation of Electroacoustic Properties of Experimental Fibre-Optic Microphone Designs

Fibre optic sensors have many advantages such as compactness and immunity to electromagnetic interference, making them suitable for infrastructure monitoring and shape reconstruction in minimally invasive surgical tools. In this study, we present different implementations of a fibre-optic acoustic sensor based on fibre-optic strain measurements. Using the range-resolved interferometry approach, based on sinusoidal modulation of the optical wavelength of a cost-effective laser diode, fibre segment interferometry allows high-resolution fibre optic strain measurements. In contrast to existing approaches, this allows measurements over user-definable gauge lengths up to the metre range. This work investigates different design approaches for the conversion of acoustic signals into fibre-optic strain. In comparing the approaches, we focus on the sensitivity, signal-to-noise ratio, and the resonance behaviour of the system. Our aim is to estimate the potentials and drawbacks of the working principle in order to identify use cases where it excels.