Ultrafast laser ablation of silica optical fibers for fabrication of diaphragm/cantilever-based acoustic sensors

We present our recent progress in fiber optic acoustic sensors formed by using a Fabry–Perot (FP) interferometer with a silica diaphragm/cantilever on the tip of a single-mode fiber, fabricated by the femtosecond (fs) laser ablation technique. The directivity of an acoustic sensor with a silica diaphragm was improved by packaging the sensor head in a capillary tube coated with an acoustically absorbing wax film. The measurement results demonstrated a substantial increase in directivity with this packaging method. A cantilever beam diaphragm based FP tip was further investigated to improve the sensor performance. This sensor structure is insensitive to Q-point drift. In addition, the sensing frequency range can be flexibly controlled by designing the dimension of the cantilever beam, indicating the flexibility of sensor fabrication by fs laser micromachining.