Pressure Sensitivity of a Fiber-Optic Microprobe for High-Frequency Ultrasonic Field

An acoustic microprobe is required to measure high-frequency ultrasonic fields with good spatial resolution. An optical fiber microprobe was proposed in our previous study, which consists of a small optical cavity 100 µm long made at the end of the fiber. The optical path length of the cavity is changed by the applied acoustic field, and the modulation of output light intensity is monitored at the other end of the fiber to derive information of the acoustic field. In the present study, the pressure sensitivity of the fiber-optic microprobe is discussed theoretically and experimentally. Mechanical deformation of the optical cavity by acoustic pressure is calculated by the finite element method (FEM), and the effect of the deformation on the optical property is analyzed for a low finesse microcavity.