[1] Yuan L B. Multi-core fiber characteristics and its sensing applications[J]. Laser & Optoelectronics Progress, 56, 170612(2019).

[2] Chi R H, Zhou Y P, Li L Y. Research status and development analysis of multicore fiber amplifier[J]. Laser & Optoelectronics Progress, 56, 190005(2019).

[3] Duncan R G, Froggatt M E, Kreger S T et al. High-accuracy fiber-optic shape sensing[J]. Proceedings of SPIE, 6530, 65301S(2007).

[4] Yin G L, Lu L, Zhou L et al. Distributed directional torsion sensing based on an optical frequency domain reflectometer and a helical multicore fiber[J]. Optics Express, 28, 16140-16150(2020).

[5] Zhao Z Y, Dang Y L, Tang M et al. Spatial-division multiplexed hybrid Raman and Brillouin optical time-domain reflectometry based on multi-core fiber[J]. Optics Express, 24, 25111-25118(2016).

[6] Zhao Z Y, Tang M, Wang L et al. Distributed vibration sensor based on space-division multiplexed reflectometer and interferometer in multicore fiber[J]. Journal of Lightwave Technology, 36, 5764-5772(2018).

[7] Nakazawa M. Rayleigh backscattering theory for single-mode optical fibers[J]. Journal of the Optical Society of America, 73, 1175-1180(1983).

[8] Healey P. Fading in heterodyne OTDR[J]. Electronics Letters, 20, 30-32(1984).

[9] Gabai H, Shpatz I, Eyal A. Lumped Rayleigh reflectors[J]. Optics Letters, 42, 4529-4532(2017).

[10] Redding B, Murray M J, Donko A et al. Low-noise distributed acoustic sensing using enhanced backscattering fiber with ultra-low-loss point reflectors[J]. Optics Express, 28, 14638-14647(2020).

[11] Pan Z Q, Liang K Z, Zhou J et al. Interference-fading-free phase-demodulated OTDR system[J]. Proceedings of SPIE, 8421, 842129(2012). http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1381344

[12] Wang X, Lu B, Wang Z Y et al. Interference-fading-free Phi-OTDR based on differential phase shift pulsing technology[J]. IEEE Photonics Technology Letters, 31, 39-42(2019).

[13] Zhou J, Pan Z Q, Ye Q et al. Phase demodulation technology using a multi-frequency source for discrimination of interference-fading induced false alarms in a φ-OTDR system[J]. Chinese Journal of Lasers, 40, 0905003(2013).

[14] Zhou J, Pan Z Q, Ye Q et al. Characteristics and explanations of interference fading of a Φ-OTDR with a multi-frequency source[J]. Journal of Lightwave Technology, 31, 2947-2954(2013).

[15] Chen D A, Liu Q W, He Z Y. Phase-detection distributed fiber-optic vibration sensor without fading-noise based on time-gated digital OFDR[J]. Optics Express, 25, 8315-8325(2017).

[16] Hartog A H, Liokumovich L B, Ushakov N A et al. The use of multi-frequency acquisition to significantly improve the quality of fibre-optic-distributed vibration sensing[J]. Geophysical Prospecting, 66, 192-202(2018).

[17] Liang C L, Lu Y, Zhang X L et al. Fading noise reduction utilizing multi-wavelength scheme in phase interrogation based phase-sensitive optical time domain reflectometry[C]∥2018 Asia Communications and Photonics Conference (ACP), October 26-29, 2018, Hangzhou, China.(2018).

[18] Ma H Y, Wang X X, Ma F et al. Research progress of Φ-OTDR distributed optical fiber acoustic sensor[J]. Laser & Optoelectronics Progress, 57, 130005(2020).

[19] Cai H W, Ye Q, Wang Z Y et al. Distributed optical fiber acoustic sensing technology based on coherent Rayleigh scattering[J]. Laser & Optoelectronics Progress, 57, 050001(2020).

[20] Takenaga K, Tanigawa S, Guan N et al. Reduction of crosstalk by quasi-homogeneous solid multi-core fiber[C]∥2010 Conference on Optical Fiber Communication (OFC/NFOEC), Collocated National Fiber Optic Engineers Conference, March 21-25, 2010, San Diego, CA, USA.(2010).

[21] Liu C, Pei L, Xie Y H et al. Design of low crosstalk few mode multi-core fiber based on heterogeneous structure[J]. Chinese Journal of Lasers, 47, 1106004(2020).

[22] Gabai H, Eyal A. On the sensitivity of distributed acoustic sensing[J]. Optics Letters, 41, 5648-5651(2016).