Fig. 1. Multi-beam interference model of Fabry-Perot microcavity

Fig. 2. Reflected beam and fiber coupling model of Fabry-Perot cavity

Fig. 3. Configuration of three spliced air gap-based Fabry-Perot sensor^[38]

Fig. 4. Experiment results of all-sapphire single-crystal fiber Fabry-Perot sensor fabricated by femtosecond laser micro-machining and CO₂ laser welding^[40]. (a)(b) Microscopic and scanning electron microscopic image of the bottom surface of the pit before the CO₂ laser surface smoothing; (c)(d) corresponding microscopic and scanning electron microscopic image after the CO₂ laser surface smoothing; (e) image of the laser-welded sensor head (the inset shows the image of at the welding plane); (f) image of the fabricated sensor head

Fig. 5. Schematic diagrams of thin-film fiber-optic Fabry-Perot microcavity sensor and sensing system^[41]

Fig. 6. Schematic diagram of 45° inclined fiber diaphragm sensor head^[46]. (a) Sensing optical path diagram of 45°inclined optical fiber diaphragm sensor;(b) axial diagram of 45° inclined fiber diaphragm sensor

Fig. 7. Actual picture of the flame experiment of the patch type sapphire fiber Fabry-Perot sensor

Fig. 8. Parallel dual-waveguide Fabry-Perot high temperature sensor^[50]. (a) Structure diagram of the sensor; (b) schematic diagram of the sensing optical path

Fig. 9. Schematic diagram of laser micromachined composite Fabry-Perot sensor^[51]

Fig. 10. Micrograph of the composite fiber-optic Fabry-Perot sensor made by the etching method combined with the optical fiber splicing technology^[52]

Fig. 11. Special fiber splicing composite Fabry-Perot sensor^[53]_. (a) Schematic diagram; (b) micrograph

Fig. 12. Structure and sensing characteristics of all-silicon dual-cavity optical fiber pressure sensor^[55]. (a) Schematic diagram of the all-silicon-based dual-cavity fiber-optic pressure sensor structure (all the components are high-temperature resistant materials); (b) interference model of the dual-cavity structure with three reflective mirrors; (c) simulation of reflected spectra I_R(λ) (simulation parameters: n₁=1, n₂=3.47, L₁=60 μm, L₂=300 μm, I₀ is the light intensity of a broadband light source with a central wavelength of 1550 nm)

Fig. 13. Schematic diagram of structure and sensing principle of pure sapphire crystal bonded F-P sensor^[56]. (a) Schematic of the sensor structure; (b) sensor sensing principle and spectrum curve diagram