Highly Sensitive Phase-Front-Modulation Fiber Acoustic Sensor

We report a new low-noise compact fiber acoustic sensor that implements a microfabricated silicon diaphragm with a π/2 phase step combined to a single-mode fiber to form a simple interferometric sensor head. Compared to high-sensitivity diaphragm-based fiber Fabry–Perot sensors, this sensor has a similar strain resolution, it operates over a much broad range of wavelengths (∼±150 nm), its response depends very weakly on temperature and on the distance between the fiber and the diaphragm, and both microfabrication and assembly are simpler. A prototype sensor is reported with an average minimum detectable pressure as low as 5.4 μPa/√Hz between 1 and 30 kHz, in agreement with a theoretical model.