Fig. 1. Schematic diagram of frequency modulated continuous wave interferometer. (a) Michelson interferometer structure; (b) laser linear sweep light

Fig. 2. Rayleigh scattering of standard single-mode fibers is enhanced by UV laser exposure^[17]. (a) Schematic diagram of exposure area of UV laser exposure method; (b) Gain spectrum of Rayleigh scattering enhanced single mode fiber with optimal exposure parameters

Fig. 3. Fabrication of weak scattering point array (WSPA) in SMF using femtosecond laser self-focusing technique^[11]. (a) Schematic diagram of WSPA processing; (b) obtained Rayleigh scattering enhanced spectrum of WSPA

Fig. 4. Fabrication of weak scattering point array (WSPA) in each core of multicore fiber using femtosecond laser self-focusing technique^[18]

Fig. 5. Micro-cavity arrays fabricated by femtosecond laser micro-machining technology^[19]

Fig. 6. Fabrication of weak fiber Bragg grating (WFBG) array in SMF using femtosecond laser technology^［22］. (a) Distance domain spectra of 200 identical WFBG; (b) enlarged view of the 89th to 92nd grating

Fig. 7. Zero crossing resampling(ZCR) method and instantaneous optical frequency domain(IOFR) method eliminate nonlinear frequency sweep of light source^[30]. (a) Schematic diagram of ZCR method; (b) schematic diagram of IOFR method; (c) obtained Rayleigh scattering spectra of optical fiber under test using uncompensated method, zero-crossing resampling method and instantaneous optical frequency resampling method

Fig. 8. Flow chart of the post-processing method based on combining distance compensation and image wavelet denoising^[7]

Fig. 9. Distributed high temperature sensing based on obtained weak micro-cavity array (WMCA)^[19]. (a) Schematic of WMCA placed in the tube furnace; (b) measured optical frequency shift of WMCA with temperature change；（c）temperature variation in areas from 2.50 to 2.55 m

Fig. 10. Distributed strain sensing based on standard single-mode fiber and UV-exposed Rayleigh scattering enhanced fiber^[17]. (a) Standard single-mode fiber strain sensing; (b）UV-exposed Rayleigh scattering enhanced fiber strain sensing

Fig. 11. Multi-core fiber 3D shape sensing technology based on vector projection^[18]