Extrinsic F-P interferometric fiber ultrasonic sensor using two-photon polymerization 3D printing

Fiber-based F-P resonators have been widely used in ultrasonic detection and photoacoustic detection. The planar-concave F-P resonator has gradually replaced the planar F-P resonator due to its ability to provide lateral confinement of light beam. However, the planar-concave F-P requires curved concavity and wavefront matching for better sensitivity. Here, planar-concave F-P resonator with additional waveguide was reported, which not only provides lateral confinement but also effectively addresses the curvature matching issue. Through two-photon polymerization 3D printing technology, the photoresist with low absorption and high refractive index at 1.55 μm band was selected, we obtained prefabricated structures of desired dimensions.The ultrasonic sensor with detection limit of 23 KPa and a bandwidth of 20 MHz was obtained, as well the noise equivalent pressure (NEP) is 23Pa/√Hz in 1 MHz detection.