[1] Zhao L J, Zhang X Z, Xu Z N et al. Influencing factors of IQ demodulation method in distributed acoustic sensors[J]. Acta Optica Sinica, 43, 1428001(2023).

[2] Yuan L B, Tong W J, Jiang S et al. Road map of fiber optic sensor technology in China[J]. Acta Optica Sinica, 42, 0100001(2022).

[3] Nazarathy M, Newton S A, Giffard R P et al. Real-time long range complementary correlation optical time domain reflectometer[J]. Journal of Lightwave Technology, 7, 24-38(1989).

[4] Wang Z N, Zeng J J, Li J et al. Ultra-long phase-sensitive OTDR with hybrid distributed amplification[J]. Optics Letters, 39, 5866-5869(2014).

[5] Liu Q W, Fan X Y, He Z Y. Time-gated digital optical frequency domain reflectometry with 1.6-m spatial resolution over entire 110-km range[J]. Optics Express, 23, 25988-25995(2015).

[6] Loranger S, Parent F, Lambin-Iezzi V et al. Enhancement of Rayleigh scatter in optical fiber by simple UV treatment: an order of magnitude increase in distributed sensing sensitivity[J]. Proceedings of SPIE, 9744, 97440E(2016).

[7] Redding B, Murray M J, Donko A et al. Low-noise distributed acoustic sensing using ultra-low- loss, enhanced-backscatter fiber[C], T3.11(2021).

[8] Parent F, Loranger S, Mandal K K et al. Enhancement of accuracy in shape sensing of surgical needles using optical frequency domain reflectometry in optical fibers[J]. Biomedical Optics Express, 8, 2210-2221(2017).

[9] Westbrook P S, Feder K S, Kremp T et al. Enhanced optical fiber for distributed acoustic sensing beyond the limits of Rayleigh backscattering[J]. iScience, 23, 101137(2020).

[10] Brinkmeyer E. Analysis of the backscattering method for single-mode optical fibers[J]. Journal of the Optical Society of America, 70, 1010-1012(1980).

[11] Yang Z M, Xu S Q, Yang J H et al. Research progress of photosensitive glass with a modulation of refractive index induced by the exposure to UV light[J]. Journal of the Chinese Ceramic Society, 31, 981-985, 990(2003).

[12] Jiang J F, Zhang Y M, Liu T G et al. Review on photosensitivity mechanisms of Ge-doped optical fibers and methods for enhancing photosensitivity[J]. Optical Technology, 29, 131-135(2003).

[13] Kashyap R[M]. Fiber Bragg gratings, 18-25(2009).

[14] Brochu G, LaRochelle S, Ayotte N. Dynamics of hydrogen diffusion as a key component of the photosensitivity response of hydrogen-loaded optical fibers[J]. Journal of Lightwave Technology, 27, 3123-3134(2009).

[15] Loranger S, Gagné M, Lambin-Iezzi V et al. Rayleigh scatter based order of magnitude increase in distributed temperature and strain sensing by simple UV exposure of optical fibre[J]. Scientific Reports, 5, 11177(2015).

[16] Du C, Fu C L, Li P F et al. High-spatial-resolution strain sensor based on Rayleigh-scattering-enhanced SMF using direct UV exposure[J]. Journal of Lightwave Technology, 41, 1566-1570(2023).

[17] Wen J X, Peng G D, Luo W Y et al. Gamma irradiation effect on Rayleigh scattering in low water peak single-mode optical fibers[J]. Optics Express, 19, 23271-23278(2011).

[18] Jin J, Zhang H S, Liu J X et al. Distributed temperature sensing based on Rayleigh scattering in irradiated optical fiber[J]. IEEE Sensors Journal, 16, 8928-8935(2016).

[19] Guo H Y, Tang J G, Li X F et al. On-line writing identical and weak fiber Bragg grating arrays[J]. Chinese Optics Letters, 11, 030602(2013).

[20] Zaitsev I A, Butov O V, Voloshin V V et al. Optical fiber with distributed Bragg-type reflector[J]. Journal of Communications Technology and Electronics, 61, 639-645(2016).

[21] Westbrook P S, Feder K S, Ortiz R M et al. Kilometer length, low loss enhanced back scattering fiber for distributed sensing[C](2017).

[22] Monet F, Loranger S, Lambin-Iezzi V et al. The ROGUE: a novel, noise-generated random grating[J]. Optics Express, 27, 13895-13909(2019).

[23] Li Z Y, Sun W F, Wang H H. Research on the ultra-weak reflective fiber Bragg grating sensing technology based on optical frequency domain reflection technology[J]. Acta Optica Sinica, 35, 0806003(2015).

[24] Erdogan T, Mizrahi V, Lemaire P J et al. Decay of ultraviolet-induced fiber Bragg gratings[J]. Journal of Applied Physics, 76, 73-80(1994).

[25] Dong X R, Wang Z A, Zeng L et al. Reflection spectral characteristics of Bragg gratings fabricated via femtosecond laser phase mask technique[J]. Chinese Journal of Lasers, 50, 1906001(2023).

[26] Yan A D, Huang S, Li S et al. Distributed optical fiber sensors with ultrafast laser enhanced Rayleigh backscattering profiles for real-time monitoring of solid oxide fuel cell operations[J]. Scientific Reports, 7, 9360(2017).

[27] Ai F. Investigation on Discrete enhanced fiber based distributed sensing technologies and their applications[D], 47-60(2019).

[28] Liu D M, He T, Xu Z J et al. New type of microstructure-fiber distributed acoustic sensing technology and its applications[J]. Journal of Applied Sciences, 38, 296-309(2020).

[29] Zhang W. Research on high spatial resolution distributed optical fiber sensing technology based on longitudinal microstructure fiber[D], 23-45(2020).

[30] Meng Y J, Fu C L, Chen L et al. Submillimeter-spatial-resolution φ‑OFDR strain sensor using femtosecond laser induced permanent scatters[J]. Optics Letters, 47, 6289-6292(2022).

[31] Chen Z, Yuan L, Hefferman G et al. Ultraweak intrinsic Fabry-Perot cavity array for distributed sensing[J]. Optics Letters, 40, 320-323(2015).

[32] Peng Z Q, Wen H Q, Jian J N et al. Identifications and classifications of human locomotion using Rayleigh-enhanced distributed fiber acoustic sensors with deep neural networks[J]. Scientific Reports, 10, 21014(2020).

[33] Li W C, Liu J X, Li S C et al. In-fiber integrated quasi-distributed temperature sensor array with high spatial resolution for silicon nitride igniter[J]. IEEE Sensors Journal, 22, 9426-9432(2022).

[34] Esposito F, Ranjan R, Campopiano S et al. Arc-induced long period gratings from standard to polarization-maintaining and photonic crystal fibers[J]. Sensors, 18, 918(2018).

[35] Rego G, Ivanov O. Investigation of the mechanisms of formation of long-period gratings arc-induced in pure-silica-core fibres[J]. Optics Communications, 284, 2137-2140(2011).

[36] Liu X J, Yang Y H, Zhang X Z et al. Fabrication technology of phase shifted fiber Bragg grating with an arc discharge technique[J]. Chinese Journal of Lasers, 40, 0505002(2013).

[37] Rego G. Fibre optic devices produced by arc discharges[J]. Journal of Optics, 12, 113002(2010).

[38] Zhao Y S, Huang S, Cui Z R et al. Electric-arc-induced strength-controllable weak polarization mode coupling in polarization maintaining fiber[J]. Applied Optics, 57, 6446-6450(2018).

[39] Friebele E J, Griscom D L, Sigel G H,. Defect centers in a germanium-doped silica-core optical fiber[J]. Journal of Applied Physics, 45, 3424-3428(1974).

[40] Tsai T E, Saifi M A, Friebele E J et al. Correlation of defect centers with second-harmonic generation in Ge-doped and Ge–P-doped silica-core single-mode fibers[J]. Optics Letters, 14, 1023-1025(1989).

[41] Mahmoud F, Müller H R, Mörl K et al. Scattering loss in Nd-doped silica based optical fibers[J]. Optik, 113, 421-424(2002).

[42] Chaccour L. Rayleigh backscattered signal enhancement in highly GeO2-doped-core silica fibers[J]. IEEE Photonics Technology Letters, 34, 345-348(2022).

[43] Blanc W, Guillermier C, Dussardier B. Composition of nanoparticles in optical fibers by secondary ion mass spectrometry[J]. Optical Materials Express, 2, 1504-1510(2012).

[44] Blanc W, Mauroy V, Nguyen L et al. Fabrication of rare earth-doped transparent glass ceramic optical fibers by modified chemical vapor deposition[J]. Journal of the American Ceramic Society, 94, 2315-2318(2011).

[45] Blanc W, Dussardier B. Formation and applications of nanoparticles in silica optical fibers[J]. Journal of Optics, 45, 247-254(2016).

[46] Tosi D, Molardi C, Sypabekova M et al. Enhanced backscattering optical fiber distributed sensors: tutorial and review[J]. IEEE Sensors Journal, 21, 12667-12678(2021).

[47] Ayupova T, Shaimerdenova M, Korganbayev S et al. Fiber optic refractive index distributed multi-sensors by scattering-level multiplexing with MgO nanoparticle-doped fibers[J]. IEEE Sensors Journal, 20, 2504-2510(2020).

[48] Korganbayev S, Shaimerdenova M, Ayupova T et al. Refractive index sensor by interrogation of etched MgO nanoparticle-doped optical fiber signature[J]. IEEE Photonics Technology Letters, 31, 1253-1256(2019).

[49] Beisenova A, Issatayeva A, Iordachita I et al. Distributed fiber optics 3D shape sensing by means of high scattering NP-doped fibers simultaneous spatial multiplexing[J]. Optics Express, 27, 22074-22087(2019).

[50] Beisenova A, Issatayeva A, Korganbayev S et al. Simultaneous distributed sensing on multiple MgO-doped high scattering fibers by means of scattering-level multiplexing[J]. Journal of Lightwave Technology, 37, 3413-3421(2019).

[51] Beisenova A, Issatayeva A, Sovetov S et al. Multi-fiber distributed thermal profiling of minimally invasive thermal ablation with scattering-level multiplexing in MgO-doped fibers[J]. Biomedical Optics Express, 10, 1282-1296(2019).

[52] Sypabekova M, Korganbayev S, Blanc W et al. Fiber optic refractive index sensors through spectral detection of Rayleigh backscattering in a chemically etched MgO-based nanoparticle-doped fiber[J]. Optics Letters, 43, 5945-5948(2018).

[53] Tosi D, Molardi C, Blanc W. Rayleigh scattering characterization of a low-loss MgO-based nanoparticle-doped optical fiber for distributed sensing[J]. Optics & Laser Technology, 133, 106523(2021).

[54] Fuertes V, Grégoire N, Labranche P et al. Engineering nanoparticle features to tune Rayleigh scattering in nanoparticles-doped optical fibers[J]. Scientific Reports, 11, 9116(2021).

[55] Fuertes V, Grégoire N, Labranche P et al. Tunable Rayleigh scattering in low-loss Sr-based nanoparticle-doped optical fibers: controlling nanoparticle features throughout preform and fiber fabrication[J]. Journal of Alloys and Compounds, 940, 168928(2023).

[56] Fuertes V, Grégoire N, Labranche P et al. Customizing nanoparticle characteristics in Ba-rich nanoparticle-doped optical fibers to tune Rayleigh scattering[J]. Journal of Non-Crystalline Solids, 614, 122398(2023).

[57] Wang X, Benedictus R, Groves R M. Spectral characteristics of gold nanoparticle doped optical fibre under axial strain[J]. Scientific Reports, 12, 16593(2022).

[58] Wang Z, Ren G B, Lou S Q et al. Loss properties due to Rayleigh scattering in different types of fiber[J]. Optics Express, 11, 39-47(2003).

[59] Andreev V A, Burdin V A, Troshin A V. Analysis of spectral characteristics of Rayleigh scattering parameters for different types of single-mode fibers[J]. Proceedings of SPIE, 6277, 627708(2006).

[60] Pournoury M, Moon D S, Nazari T et al. Low scattering loss fiber with segmented-core and depressed inner cladding structure[J]. Optics Communications, 317, 13-17(2014).

[61] Kreger S T, Sang A K, Gifford D K et al. Distributed strain and temperature sensing in plastic optical fiber using Rayleigh scatter[J]. Proceedings of SPIE, 7316, 73160A(2009).

[62] Dengler S A, Engelbrecht R, Schmauss B. Absolute spectral backscatter measurements of large-core multimode PMMA polymer optical fibers[J]. Optics Express, 29, 34629-34640(2021).

[63] Sugita T. Optical time-domain reflectometry of bent plastic optical fibers[J]. Applied Optics, 40, 897-905(2001).

[64] Lenke P, Liehr S, Krebber K. Improvements of the distributed strain sensor based on optical time domain reflectometry measurement in polymer optical fibers[C](2008).

[65] Liehr S, Lenke P, Wendt M et al. Perfluorinated graded-index polymer optical fibers for distributed measurement of strain[C](2008).

[66] Mao Y, Ashry I, Hveding F et al. Simultaneous distributed acoustic and temperature sensing using a multimode fiber[J]. IEEE Journal of Selected Topics in Quantum Electronics, 26, 5600207(2020).

[67] Zhou Z C, Cui W D, Xi X M et al. Real-time temperature measurement of high-power fiber laser core and its applications[J]. Acta Optica Sinica, 43, 1714006(2023).

[68] Wang M, Wu H, Tang M et al. Few-mode fiber based Raman distributed temperature sensing[J]. Optics Express, 25, 4907-4916(2017).

[69] Chen M M, Masoudi A, Parmigiani F et al. Distributed acoustic sensor based on a two-mode fiber[J]. Optics Express, 26, 25399-25407(2018).

[70] Lu L D, Su X C, Zhang C L et al. A novel distributed vibration sensor based on fading noise reduction in multi-mode fiber[J]. Sensors, 22, 8028(2022).

[71] Ekechukwu G, Sharma J. Degradation analysis of single-mode and multimode fibers in a full-scale wellbore and its impact on DAS and DTS measurements[J]. IEEE Sensors Journal, 23, 9287-9300(2023).

[72] Zhang R, Li X B, Xia T et al. Optimized design on multimode fiber with enhanced spontaneous Raman scattering for distributed temperature sensing[J]. Optical Engineering, 51, 084401(2012).

[73] Guo J T, Xia T, Zhang R et al. A novel multimode fiber for distributed temperature sensing based on anti-stokes Raman scattering[C](2013).

[74] Westbrook P S, Feder K S, Kremp T et al. Integrated optical fiber shape sensor modules based on twisted multicore fiber grating arrays[J]. Proceedings of SPIE, 8938, 89380H(2014).

[75] Kashima N, Uchida N, Ishida Y. Excess loss caused by the outer layer in a multimode step-index optical fiber: theory[J]. Applied Optics, 16, 2732-2737(1977).

[76] Opielka D, Rittich D. Transmission loss caused by an angular misalignment between two multimode fibers with arbitrary profile exponents[J]. Applied Optics, 22, 991-994(1983).

[77] van Etten W, Lambo W, Simons P. Loss in multimode fiber connections with a gape[J]. Applied Optics, 24, 970-976(1985).

[78] Li J, Zhang M J. Physics and applications of Raman distributed optical fiber sensing[J]. Light: Science & Applications, 11, 128(2022).

[79] Tan T, Duan C, Tian Y et al. Scattering characteristics of over 3 km long adiabatic tapered single mode fiber[J]. Journal of Lightwave Technology, 41, 4130-4136(2023).