External fibre Fabry-Perot acoustic sensor based on a photonic-crystal mirror

摘要

We demonstrate an acoustic sensor based on a Fabry-Perot interferometerformed by a single-mode fibre and an external silicon photonic-crystal mirror. Measurements in air indicate that this sensor has a relatively uniform frequency response up to at least 50 kHz, and detects pressures as low as 18 (mu)Pa Hz~(-1/2). This limit is four orders of magnitude lower than in similar types of acoustic fibre sensors. The sensor response agrees with mechanical calculations to within a few dB. We predict that this sensor has the potential to detect pressures as low as 600 nPa Hz~(-1/2), corresponding to the ambient thermal noise level in air at room temperature.