Fig. 1

(a) Schematic diagram of ultrasound detection based on the F–P cavity. The red area is the fiber core, the light blue area is the first inner cladding of the fiber, and the yellow area is the gold film formed by gold plating on the end face of the fiber. In addition, the arc part is the structure made of photoresist, and the F–P cavity is formed with the end face of the fiber. (b) Pattern layout of the F–P cavity using design software to create a model diagram corresponding to the arc-shaped part of (a)