Fig. 1. Backscattering signal. (a) Coherent fading phenomenon; (b) comparison of scattering enhancement signal and Rayleigh scattering signal

Fig. 2. Fabrication process of scattering enhanced microstructure fiber. (a) Drawing of online grating technology preparation system for wire drawing tower^[14]; (b) OTDR trace map of UWFBG array^[14]; (c) comparison of signals of scattering enhanced fiber and ordinary single mode fiber^[16]

Fig. 3. UV-transparent fiber on-line fabrication and its results. (a) Online grating technology based on UV coated optical fibers^[18]; (b) discrete scattering enhanced fiber^[12]; (c) continuous scattering enhanced fiber^[19]; (d) hybrid encoding grating array spectra^[20]; (e) gradient scattering enhanced fiber spectra^[21]

Fig. 4. Colorless weak reflection point fabrication and its result. (a) Colorless weak reflection point preparation system diagram; (b) comparison of fiber backscattered light signals before and after preparation

Fig. 5. Typical DAS performance improvement scheme based on scattering enhanced fiber. (a) Low frequency drift compensation scheme^[29]; (b) frequency response band expansion scheme^[33]; (c) detection distance expansion scheme^[21]; (d) spatial resolution improving scheme^[30]

Fig. 6. Secondary coated WFBG array fiber optic cable^[41]. (a) Schematic diagram of WFBG array fiber; (b) time domain reflected light intensity of WFBG array fiber; (c) physical image of WFBG array fiber

Fig. 7. Backscatter enhanced fiber quasi distributed sensitization array^[12]. (a) Schematic diagram of backscatter enhanced fiber; (b) backscatter intensity of backscatter enhanced fiber; (c) array diagram

Fig. 8. Fully distributed sensitization optical cable^[46]. (a) Schematic diagram; (b) physical image

Fig. 9. Basic structure and sensing principle of OFDR

Fig. 10. High density scattering enhanced fiber. (a) Ge doped photonic crystal fiber^[63]; (b) continuously exposed single mode fiber^[64]; (c) UV exposed transparent UV coated fiber^[19]

Fig. 11. Shape sensing fiber. (a) Parallel multi-core fiber with engraved Bragg grating^[68];(b) scattering enhanced fiber parallel fiber cluster^[69]; (c) spiral multi-core fiber with engraved Bragg grating^[72]; (d) spiral fiber cluster of scattering enhanced fiber^[73]