[1] [1] BAO X, CHEN L. Recent progress in distributed fiber optic sensors[J]. Sensors, 2012, 12(7): 8601-8639.

[3] [3] BAO X, CHEN L. Recent progress in optical fiber sensors based on Brillouin scattering at university of Ottawa[J]. Photonic Sensors, 2011, 1(2): 102-117.

[4] [4] WOLFGANG R H, KREBBER K. Fiber-optic sensor applications in civil and geotechnical engineering[J]. Photonic Sensors, 2011, 1(3): 268-280.

[5] [5] NG W P, LALAM N. Performance improvement of Brillouin based distributed fiber sensors employing wavelength diversity techniques[C]// 16th International Conference on Optical Communications and Networks (ICOCN), August 7-10, 2017, Wuzhen, China. New York: IEEE, 2017: 8121531-1-8121531-3.

[6] [6] LI Y, ZHANG L, FAN H, et al. Rayleigh Brillouin optical time-domain analysis system using heterodyne detection and wavelength scanning[J]. Optical Engineering, 2018, 57(5): 056112-1-056112-7.

[7] [7] XU Z, ZHAO L. Estimation of error in Brillouin frequency shift in distributed fiber sensor[J]. IEEE Sensors Journal, 2020, 20(4): 1829-1837.

[8] [8] XU Z, ZHAO L. Accurate and ultra-fast estimation of Brillouin frequency shift for distributed fiber sensors[J]. Sensors & Actuators: A. Physical, 2020, 303: 111822-1-111822-6.

[9] [9] ESSIAMBRE R J, KRAMER G, WINZER P J, et al. Capacity limits of optical fiber networks[J]. Journal of Lightwave Technology, 2010, 28(4): 662-701.

[10] [10] LI A, WANG Y, FANG J, et al. Few-mode fiber multi-parameter sensor with distributed temperature and strain discrimination[J]. Optics Letters, 2015, 40(7): 1488-1491.

[11] [11] WENG Y, IP E, PAN Z, et al. Single-end simultaneous temperature and strain sensing techniques based on Brillouin optical time domain reflectometry in few-mode fibers[J]. Optics Express, 2015, 23(7): 9024-9039.

[12] [12] BAI N, IP E, HUANG Y K, et al. Mode-division multiplexed transmission with inline few-mode fiber amplifier[J]. Optics Express, 2012, 20(3): 2668-2680.

[13] [13] NAKAZAWA M, YOSHIDA M, HIROOKA T. Measurement of mode coupling distribution along a few-mode fiber using a synchronous multi-channel OTDR[J]. Optics Express, 2014, 22(25): 31299-31309.

[14] [14] GLOGE D. Optical power flow in multimode fibers[J]. Bell System Technical Journal, 1972, 51(8): 1767-1783.

[15] [15] OLSHANSKY R. Mode coupling effects in graded-index optical fibers[J]. Applied Optics, 1975, 14(4): 935-945.

[16] [16] FURUYA K, SUEMATSU Y, TOKIWA H. Coupling length due to random bending in multimode optical fibres[J]. Optical & Quantum Electronics, 1978, 10(4): 323-330.

[17] [17] BALEMARTHY K, POLLEY A, RALPH S. Electronic equalization of multikilometer 10 Gb/s multimode fiber links: mode-coupling effects[J]. Journal of Lightwave Technology, 2006, 24(12): 4885-4894.

[18] [18] PERREY-DEBAIN E, ABRAHAMS I D, LOVE J D. A continuous model for mode mixing in graded-index multimode fibers with random imperfections[J]. Proceedings of the Royal Society A Mathematical Physical and Engineering Sciences, 2008, 464: 987-1007.

[19] [19] SHEMIRANI M B, MAO W, PANICKER R A, et al. Principal modes in graded-index multimode fiber in presence of spatial-and polarization-mode coupling[J]. Journal of Lightwave Technology, 2009, 27(10): 1248-1261.

[20] [20] JUAREZ A A, KRUNE E, WARM S, et al. Modeling of mode coupling in multimode fibers with respect to bandwidth and loss[J]. Journal of Lightwave Technology, 2014, 32(8): 1549-1558.

[21] [21] WONG N H, JUNG Y, ALAM S, et al. Numerical analysis of mode propagation and coupling in multimode fibers[C]// 2017 Opto-Electronics and Communications Conference and Photonics Global Conference, July 31-August 4, 2017, Singapore, Singapore. New York: IEEE, 2017: 8115029-1-8115029-3.

[22] [22] QIU X, WU B, LIU Y, et al. Study on mode coupling characteristics of multimode magneto-optical fibers[J]. Optics Communications, 2019, 456: 124707-1-124707-5.

[23] [23] ZHANG B, ZHANG X, ZHANG X, et al. Theory for mode coupling in perturbed fibers[J]. Optics Communications, 2020, 463: 125355-1-125355-12.

[24] [24] IMAI Y, YOSHIDA M. Polarization characteristics of fiber-optic SBS phase conjugation[J]. Optical Fiber Technology, 2000, 6(1): 42-48.

[26] [26] WEN X, WEI H C, YARON B, et al. Complete polarization control in multimode fibers with polarization and mode coupling[J]. Light: Science & Applications, 2018, 7(1): 54-64.

[27] [27] SHEN Y R. The principles of nonlinear optics[M]. New York: IEEE Journal of Quantum Electronics, 1984.

[28] [28] KOVALEV V I, HARRISON R G. Threshold for stimulated Brillouin scattering in optical fiber[J]. Optics Express, 2007, 15(26): 17625-17630.

[29] [29] ANDREY K, MICHAEL S, DIPAK C. Stimulated Brillouin scattering in optical fibers[J]. Advances in Optics and Photonics, 2010, 2(1): 1-59.

[30] [30] MOCOFANESCU A, WANG L, JAIN R, et al. SBS threshold for single mode and multimode GRIN fibers in an all fiber configuration[J]. Optics Express, 2005, 13(6): 2019-2024.

[31] [31] TEI K, TSURUOKA Y, UCHIYAMA T, et al. Stimulated Brillouin scattering in multimode optical fibers[C]// XIII International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference, September 18-22, 2000, Florence, Italy. Florence: SPIE, 2001, 4184: 490-493.

[32] [32] TEI K, TSURUOKA Y, UCHIYAMA T, et al. Critical power of stimulated Brillouin scattering in multimode optical fibers[J]. Japanese Journal of Applied Physics, 2001, 40(5): 3191-3194.

[33] [33] MASSEY S M, RUSSELL T H. The effect of phase conjugation fidelity on stimulated Brillouin scattering threshold[J]. IEEE Journal of Selected Topics in Quantum Electronics, 2009, 15(2): 399-405.

[34] [34] IEZZI V L, LORANGER S, HARHIRA A, et al. Stimulated Brillouin scattering in multi-mode fiber for sensing applications[C]// 7th International Workshop on Fibre and Optical Passive Components, July 13-15, 2011, Montreal, Canada. New York: IEEE, 2011: 1-4.

[35] [35] LU H, ZHOU P, WANG X, et al. Theoretical and numerical study of the threshold of stimulated Brillouin scattering in multimode fibers[J]. Journal of Lightwave Technology, 2015, 33(21): 4464-4470.

[36] [36] KE W W, WANG X J, TANG X. Stimulated Brillouin scattering model in multi-mode fiber lasers[J]. IEEE Journal of Selected Topics in Quantum Electronics, 2014, 20(5): 305-314.

[37] [37] KOVALEV V I, HARRISON R G. Observation of inhomogeneous spectral broadening of stimulated Brillouin scattering in an optical fiber[J]. Physical Review Letters, 2000, 85(9): 1879-1882.

[38] [38] MINARDO A, BERNINI R, ZENI L. Experimental and numerical study on stimulated Brillouin scattering in a graded-index multimode fiber[J]. Optics Express, 2014, 22(14): 17480-17489.

[39] [39] XU Y, REN M, LU Y, et al. Multi-parameter sensor based on stimulated Brillouin scattering in inverse-parabolic graded-index fiber[J]. Optics Letters, 2016, 41(6): 1138-1141.

[40] [40] ZHANG Z, LU Y, PAN Y, et al. Trench-assisted multimode fiber used in Brillouin optical time domain sensors[J]. Optics Express, 2019, 27(8): 11396-11405.

[41] [41] SODHI S S, JACKMAN W S. Strain measurement in multimode fibers using Brillouin optical time-domain reflectometry[C]// Optical Fiber Communication Conference and Exhibit, February 22-27, 1998, San Jose, USA. New York: IEEE, 1998: 181-182.

[43] [43] DONG Y, XU P, ZHANG H, et al. Characterization of evolution of mode coupling in a graded-index polymer optical fiber by using Brillouin optical time-domain analysis[J]. Optics Express, 2014, 22(22): 26510-26516.

[45] [45] SJOBERG M, QUIROGA-TEIXEIRO M L, GALT S, et al. Dependence of stimulated Brillouin scattering in multimode fibers on beam quality, pulse duration, and coherence length[J]. Journal of the Optical Society of America B, 2003, 20(3): 434-442.