Intrinsic Fiber-Optic FPI Fabricated by Femtosecond Laser
Above-mentioned fiber-optic EFPI is formed by fs-laser ablation. When fs-laser power is reduced to some extent, fiber-optic intrinsic FPI could be formed by writing weak reflective mirrors using fs laser to induce permanent refractive index change in fiber, as shown in Figure 3.13a. The typical reflectivity of such a structure was about -45 dB and the loss was about 0.02 dB measured by an optical power
Figure 3.13 (a) Confocal microscopic image of a weak reflector fabricated by fs-laser micromachining. (b) Schematic of the fiber-optic IFPI. (c) The measured reflection spectrum of the fabricated fiber-optic IFPI sensor. (Huang, J. et al. 2014. Optics Express, 22(15), 18757-18769; Wang, W. et al. 2010. Asia Communications and Photonics Conference and Exhibition (pp. 79900P-79900P). International Society for Optics and Photonics.)
meter. Two cascaded mirrors were written in the core of the fiber; an intrinsic FP interferometer (IFPI) could be achieved, as shown in Figure 3.13b. An IFPI with a cavity length of 100 |!m was demonstrated in Figure 3.13c, which could be used as temperature and strain sensors.