Fig. 1. Schematic diagram. (a)MEMS optical and acoustic sensor based on microstructured fiber grating; (b) fiber Bragg grating^[12]

Fig. 2. Schematic diagram of optical fiber interferometer acoustic sensitivity principle. (a) MI; (b) SI; (c) MZI; (d) FPI

Fig. 3. Experimental results. (a) Structure diagram of TC-ULPFG^[24]; (b) steel square plane and Co²⁺-doped FBGs; (c) scanning electron microscopy image of the crossed Co²⁺-doped micro-FBG^[8]

Fig. 4. Micro all fiber suspension core sensor. (a) Schematic diagram of FPI acoustic sensor with microfiber Bragg grating^[36]; (b) schematic diagram of suspension core sensor; (c) image of suspension core sensor^[38]

Fig. 5. Schematic diagram of optical fiber ultrasonic sensors for ultrasonic detection^[47]

Fig. 6. Sectional and physical drawings of a small hydrophone based on photonic crystal film^[52]

Fig. 7. Schematic and physical drawings of a fiber-optic Fabry-Perot acoustic sensor based on a multilayer graphene film approximately 100 nm thick^[53]

Fig. 8. Acoustic sensor based on metal film. (a) Image of fiber-optic Fabry-Perot interference acoustic sensor based on large area silver film^[60]; (b) image of fiber-optic microphone based on corrugated silver diaphragm^[61]

Fig. 9. Fiber FPI microphone. (a) Components used for assembling the bionic directional microphone; (b) cross-section view of the microphone head; (c) photograph of the as-prepared bionic directional microphone^[65]

Fig. 10. Physical diagram of coupled single-channel and double-channel semi-buried optical waveguide cavities^[21]

Fig. 11. Schematic of novel photo-acoustic sensor based on a polymer spherical microcavity fiber-optic Fizeau interferometer^[73]

Fig. 12. Optical fiber acoustic sensor based on planar concave polymer micro-resonant cavity. (a) Schematic diagram; (b) optical fiber micro-resonator sensor structure^[6]

Fig. 13. FPE type filmless optical microphone. (a) Sensing schematic diagram; (b) sound pressure sensitivity curve^[76]

Fig. 14. Experiment on sound pressure sensitive mechanism. (a) Profile of FPE on plane A-A; (b) mechanical structure drawing of FPE; (c) detection principle of acoustic detection structure^[78]

Fig. 15. Micro-fiber-optic acoustic sensor based on high quality factor FPR. (a) Physical picture; (b) sensor head size diagram^[22]

Fig. 16. Optical contact process of FPR^[22]

Fig. 17. High temperature resistance test system of all-optical membrane-free fiber-optic acoustic sensor^[80]

Fig. 18. Fiber F-P cavity based on silica glass direct bonding. (a) Bath "sandwich" F-P cavity; (b) image of fiber-optic acoustic sensor^[81]

Fig. 19. Optical resolution photoacoustic microscopy images of mouse ears obtained in vivo^[6]

Fig. 20. Photographs of physical models. (a) Ridge-like bulk; (b) misplaced rectangular bulk^[83]

Fig. 21. Images of two physical models. (a) Ridge-like bulk; (b) misplaced rectangular bulk^[83]