[1] T. Erdogan, “Fiber grating spectra,” Journal of Lightwave Technology, 1997, 15(8): 1277–1294.

[2] K. O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, “Photosensitivity in optical fiber waveguides: application to reflection filter fabrication,” Applied Physics Letters, 1978, 32(10): 647–649.

[3] G. Meltz, W. W. Morey, and W. H. Glenn, “Formation of Bragg gratings in optical fibers by a transverse holographic method,” Optics Letters, 1989, 14(15): 823–825.

[4] P. J. Lemaire, R. M. Atkins, V. Mizrahi, and W. A. Reed, “High pressure H2 loading as a technique for achieving ultrahigh UV photosensitivity, and thermal sensitivity in GeO2 doped optical fibres,” Electronics Letters, 1993, 29(13): 1191–1193.

[5] K. O. Hill, B. Malo, F. Bilodeau, D. C. Johnson, and J. Albert, “Bragg gratings fabricated in monomode photosensitive optical fiber by UV exposure through a phase mask,” Applied Physics Letters, 1993, 62(10): 1035–1037.

[6] F. Ouellette, P. A. Krug, T. Stephens, G. Dhosi, and B. Eggleton, “Broadband and WDM dispersion compensation using chirped sampled fibre Bragg gratings,” Electronics Letters, 1995, 31(11): 899–901.

[7] A. D. Kersey, M. A. Davis, H. J. Patrick, M. LeBlanc, K. P. Koo, and C. G. Askins “Fiber grating sensors,” Journal of Lightwave Technology, 1997, 15(8): 1442–1463.

[8] J. Canning, “Fibre gratings and devices for sensors and lasers,” Laser & Photonics Reviews, 2008, 2(4): 275–289.

[9] J. Yao, “Optoelectronic oscillators for high speed and high-resolution optical sensing,” Journal of Lightwave Technology, 2017, 35(16): 3489–3497.

[10] K. Itoh, W. Watanabe, S. Nolte, and C. B. Schaffer, “Ultrafast processes for bulk modification of transparent materials,” MRS Bulletin, 2006, 31(8): 620–625.

[11] M. Beresna, M. GeceviIus, and P. G. Kazansky, “Ultrafast laser direct writing and nanostructuring in transparent materials,” Advances in Optics & Photonics, 2014, 6(3): 293–339.

[12] D. Pallarés-Aldeiturriaga, P. Roldán-Varona, L. Rodríguez-Cobo, and J. M. López-Higuera, “Optical fiber sensors by direct laser processing: a review,” Sensors, 2020, 20(23): 6971.

[13] Y. Zhang, C. Lin, C. Liao, K. Yang, Z. Li, and Y. Wang, “Femtosecond laser-inscribed fiber interface Mach-Zehnder interferometer for temperature-insensitive refractive index measurement,” Optics Letters, 2018, 43(18): 4421–4424.

[14] Y. Shimotsuma, P. G. Kazansky, J. Qiu, and K. Hirao, “Self-organized nanogratings in glass irradiated by ultrashort light pulses,” Physical Review Letters, 2003, 91(24): 247405.

[15] F. Zhang, X. Xu, J. He, B. Du, and Y. Wang, “Highly sensitive temperature sensor based on a polymer-infiltrated Mach-Zehnder interferometer created in graded index fiber,” Optics Letters, 2019, 44(10): 2466–2469.

[16] K. Oi, F. Barnier, and M. Obara, “Fabrication of fiber Bragg grating by femtosecond laser interferometry,” in 14th Annual Meeting of the IEEE Lasers and Electro-Optics Society, USA, 2001, pp. 776–777.

[17] A. Dragomir, D. N. Nikogosyan, K. A. Zagorulko, P. G. Kryukov, and E. M. Dianov, “Inscription of fiber Bragg gratings by ultraviolet femtosecond radiation,” Optics Letters, 2003, 28(22): 2171–2173.

[18] S. J. Mihailov, C. W. Smelser, P. Lu, R. B. Walker, D. Grobnic, H. Ding, et al., “Fiber Bragg gratings made with a phase mask and 800-nm femtosecond radiation,” Optics Letters, 2003, 28(12): 995–997.

[19] A. Martinez, M. Dubov, I. Khrushchev, and I. Bennion, “Direct writing of fibre Bragg gratings by femtosecond laser,” Electronics Letters, 2004, 40(19): 1170–1172.

[20] D. Grobnic, C. W. Smelser, S. J. Mihailov, R. B. Walker, and P. Lu, “Fiber Bragg gratings with suppressed cladding modes made in SMF-28 with a femtosecond IR laser and a phase mask,” IEEE Photonics Technology Letters, 2004, 16(8): 1864–1866.

[21] R. J. Williams, R. G. Kr-mer, S. Nolte, and M. J. Withford, “Femtosecond direct-writing of low-loss fiber Bragg gratings using a continuous core-scanning technique,” Optics Letters, 2013, 38(11): 1918–1920.

[22] Y. Wang, Z. Li, S. Liu, C. Fu, Z. Li, Z. Zhang, et al., “Parallel-integrated fiber Bragg gratings inscribed by femtosecond laser point-by-point technology,” Journal of Lightwave Technology, 2019, 37(10): 2185–2193.

[23] X. Liu, Y. Wang, Z. Li, S. Liu, Yi. Wang, C. Fu, et al., “Low short-wavelength loss fiber Bragg gratings inscribed in a small-core fiber by femtosecond laser point-by-point technology,” Optics Letters, 2019, 44(21): 5121–5124.

[24] G. D. Marshall, R. J. Williams, N. Jovanovic, M. J. Steel, and M. J. Withford, “Point-by-point written fiber-Bragg gratings and their application in complex grating designs,” Optics Express, 2010, 18(19): 19844–19859.

[25] R. J. Williams, C. Voigtl-nder, G. D. Marshall, A. Tünnermann, S. Nolte, M. J. Steel, et al., “Point-by-point inscription of apodized fiber Bragg gratings,” Optics Letters, 2011, 36(15): 2988–2990.

[26] C. Zhang, Y. Yang, C. Wang, C. Liao, and Y. Wang, “Femtosecond-laser-inscribed sampled fiber Bragg grating with ultrahigh thermal stability,” Optics Express, 2016, 24(4): 3981–3988.

[27] K. Yang, C. Liao, S. Liu, J. He, J. Wang, and Y. Wang, “Optical fiber tag based on an encoded fiber Bragg grating fabricated by femtosecond laser,” Journal of Lightwave Technology, 2019, 38(6): 1474–1479.

[28] B. Huang and X. Shu, “Ultra-compact strain- and temperature-insensitive torsion sensor based on a line-by-line inscribed phase-shifted FBG,” Optics Express, 2016, 24(16): 17670–17679.

[29] J. Burgmeier, C. Waltermann, G. Flachenecker, and W. Schade, “Point-by-point inscription of phase-shifted fiber Bragg gratings with electro-optic amplitude modulated femtosecond laser pulses,” Optics Letters, 2014, 39(3): 540–543.

[30] S. J. Mihailov, C. W. Smelser, D. Grobnic, R. B. Walker, P. Lu, H, Ding, et al., “Bragg gratings written in all-SiO2 and Ge-doped core fibers with 800-nm femtosecond radiation and a phase mask,” Journal of Lightwave Technology, 2004, 22(1): 94–100.

[31] C. M. Jewart, Q. Wang, J. Canning, D. Grobnic, S. J. Mihailov, and K. P. Chen, “Ultrafast femtosecond-laser-induced fiber Bragg gratings in air-hole microstructured fibers for high-temperature pressure sensing,” Optics Letters, 2010, 35(9): 1443–1445.

[32] K. Yang, J. He, C. Liao, Y. Wang, S. Liu, K. Guo, et al., “Femtosecond laser inscription of fiber Bragg grating in twin-core few-mode fiber for directional bend sensing,” Journal of Lightwave Technology, 2017, 35(21): 4670–4676.

[33] A. Wolf, A. Dostovalov, K. Bronnikov, and S. Babin, “Arrays of fiber Bragg gratings selectively inscribed in different cores of 7-core spun optical fiber by IR femtosecond laser pulses,” Optics Express, 2019, 27(10): 13978–13990.

[34] L. B. Fu, G. D. Marshall, J. A. Bolger, P. Steinvurzel, E. C. Magi, M. J. Withford, et al., “Femtosecond laser writing Bragg gratings in pure silica photonic crystal fibres,” Electronics Letters, 2005, 41(11): 638–640.

[35] S. J. Mihailov, D. Grobnic, H. Ding, C. W. Smelser, and J. Broeng, “Femtosecond IR laser fabrication of Bragg gratings in photonic crystal fibers and tapers,” IEEE Photonics Technology Letters, 2006, 18(17): 1837–1839.

[36] T. Geernaert, K. Kalli, C. Koutsides, M. Komodromos, T. Nasilowski, W. Urbanczyk, et al., “Point-by-point fiber Bragg grating inscription in free-standing step-index and photonic crystal fibers using near-IR femtosecond laser,” Optics Letters, 2010, 35(10): 1647–1649.

[37] C. Wang, J. He, J. Zhang, C. Liao, Y. Wang, W. Jin, et al., “Bragg gratings inscribed in selectively inflated photonic crystal fibers,” Optics Express, 2017, 25(23): 28442–28450.

[38] S. J. Mihailov, D. Grobnic, C. W. Smelser, P. Lu, R. B. Walker, and H. Ding, “Bragg grating inscription in various optical fibers with femtosecond infrared lasers and a phase mask,” Optical Materials Express, 2011, 1(4): 754–765.

[39] N. Jovanovic, A. Fuerbach, G. D. Marshall, M. J. Withford, and S. D. Jackson, “Stable high-power continuous-wave Yb3+-doped silica fiber laser utilizing a point-by-point inscribed fiber Bragg grating,” Optics Letters, 2007, 32(11): 1486–1488.

[40] R. J. Williams, N. Jovanovic, G. D. Marshall, and M. J. Withford, “All-optical, actively Q-switched fiber laser,” Optics Express, 2010, 18(8): 7714–7723.

[41] A. Fuerbach, G. Bharathan, and M. Ams, “Grating inscription into fluoride fibers: a review,” IEEE Photonics Journal, 2019, 11(5): 1–11.

[42] D. Grobnic, S. J. Mihailov, and C. W. Smelser, “Femtosecond IR laser inscription of Bragg gratings in single-and multimode fluoride fibers,” IEEE Photonics Technology Letters, 2006, 18(24): 2686–2688.

[43] D. Grobnic, S. J. Mihailov, C. W. Smelser, and R. Walker, “Bragg gratings made with ultrafast radiation in non-silica glasses; fluoride, phosphate, borosilicate and chalcogenide Bragg gratings,” SPIE, Photonics North 2007, 6796: 67961K.

[44] G. Bharathan, T. T. Fernandez, M. Ams, R. I. Woodward, D. D. Hudson, and A. Fuerbach, “Optimized laser-written ZBLAN fiber Bragg gratings with high reflectivity and low loss,” Optics Letters, 2019, 44(2): 423–426.

[45] G. Bharathan, T. T. Fernandez, M. Ams, J. Carrée, S. Poulain, M. Poulain, et al., “Femtosecond laser direct-written fiber Bragg gratings with high reflectivity and low loss at wavelengths beyond 4 μm,” Optics Letters, 2020, 45(15): 4316–4319.

[46] D. Grobnic, S. J. Mihailov, C. W. Smelser, and H. Ding, “Sapphire fiber Bragg grating sensor made using femtosecond laser radiation for ultrahigh temperature applications,” IEEE Photonics Technology Letters, 2004, 16(11): 2505–2507.

[47] T. Elsmann, T. Habisreuther, A. Graf, M. Rothhardt, and H. Bartelt, “Inscription of first-order sapphire Bragg gratings using 400 nm femtosecond laser radiation,” Optics Express, 2013, 21(4): 4591–4597.

[48] S. Yang, D. Hu, and A. B. Wang, “Point-by-point fabrication and characterization of sapphire fiber Bragg gratings,” Optics Letters, 2017, 42(20): 4219–4222.

[49] X. Xu, J. He, C. Liao, K. Yang, K. Guo, C. Li, et al., “Sapphire fiber Bragg gratings inscribed with a femtosecond laser line-by-line scanning technique,” Optics Letters, 2018, 43(19): 4562–4565.

[50] J. Thomas, C. Voigtlander, R. G. Becker, D. Richter, A. Tunnermann, and S. Nolte, “Femtosecond pulse written fiber gratings: a new avenue to integrated fiber technology,” Laser & Photonics Reviews, 2012, 6(6): 709–723.

[51] M. Bernier, R. Vallée, B. Morasse, C. Desrosiers, A. Saliminia, and Y. Sheng, “Ytterbium fiber laser based on first-order fiber Bragg gratings written with 400nm femtosecond pulses and a phase-mask,” Optics Express, 2009, 17(21): 18887–18893.

[52] E. Wikszak, J. Thomas, J. Burghoff, B. Orta-, J. Limpert, S. Nolte, et al., “Erbium fiber laser based on intracore femtosecond-written fiber Bragg grating,” Optics Letters, 2006, 31(16): 2390–2392.

[53] M. Bernier, V. Michaud-Belleau, S. Levasseur, V. Fortin, J. Genest, and R. Vallée, “All-fiber DFB laser operating at 2.8 μm,” Optics Letters, 2015, 40(1): 81–84.

[54] G. Bharathan, R. I. Woodward, M. Ams, D. D. Hudson, S. D. Jackson, and A. Fuerbach, “Direct inscription of Bragg gratings into coated fluoride fibers for widely tunable and robust mid-infrared lasers,” Optics Express, 2017, 25(24): 30013–30019.

[55] D. Grobnic, C. W. Smelser, S. J. Mihailov, and R. B. Walker, “Long-term thermal stability tests at 1 000℃ of silica fibre Bragg gratings made with ultrafast laser radiation,” Measurement Science and Technology, 2006, 17: 1009–1013.

[56] S. C. Warren-Smith, L. V. Nguyen, C. Lang, H. Ebendorff-Heidepriem, and T. M. Monro, “Temperature sensing up to 1300℃ using suspended-core microstructured optical fibers,” Optics Express, 2016, 24(4): 3714–3719.

[57] T. Habisreuther, T. Elsmann, Z. W. Pan, A. Graf, R. Willsch, and M. A. Schmidt, “Sapphire fiber Bragg gratings for high temperature and dynamic temperature diagnostics,” Applied Thermal Engineering, 2015, 91: 860–865.

[58] K. Bronnikov, A. Wolf, S. Yakushin, A. Dostovalov, O. Egorova, S. Zhuravlev, et al., “Durable shape sensor based on FBG array inscribed in polyimide-coated multicore optical fiber,” Optics Express, 2019, 27(26): 38421–38434.

[59] S. J. Mihailov, C. W. Smelser, and D. Grobnic, “Hydrogen loading for fiber grating writing with a femtosecond laser and a phase mask,” Optics Letters, 2004, 29(18): 2127–2129.

[60] C. W. Smelser, S. J. Mihailov, and D. Grobnic, “Formation of Type I-IR and Type II-IR gratings with an ultrafast IR laser and a phase mask,” Optics Express, 2005, 13(14): 5377–5386.

[61] E. Bricchi, B. G. Klappauf, and P. G. Kazansky, “Form birefringence and negative index change created by femtosecond direct writing in transparent materials,” Optics Letters, 2004, 29(1): 119–121.

[62] J. He, Y. Wang, C. Liao, Q, Wang, K. Yang, B. Sun, et al., “Highly birefringent phase-shifted fiber Bragg gratings inscribed with femtosecond laser,” Optics Letters, 2015, 40(9): 2008–2011.

[63] F. Yang, W. Jin, Y. Lin, C. Wang, H. Lut, and Y. Tan, “Hollow-core microstructured optical fiber gas sensors,” Journal of Lightwave Technology, 2017, 35(16): 3413–3424.

[64] Y. Li, C. R. Liao, D. N. Wang, T. Sun, and K. T. V. Grattan, “Study of spectral and annealing properties of fiber Bragg gratings written in H2-free and H2-loaded fibers by use of femtosecond laser pulses,” Optics Express, 2008, 16(26): 21239–21247.

[65] C. W. Smelser, S. J. Mihailov, D. Grobnic, P. Lu, R. B. Walker, H. Ding, et al., “Multiple-beam interference patterns in optical fiber generated with ultrafast pulses and a phase mask,” Optics Letters, 2004, 29(13): 1458–1460.

[66] C. W. Smelser, D. Grobnic, and S. J. Mihailov, “Generation of pure two-beam interference grating structures in an optical fiber with a femtosecond infrared source and a phase mask,” Optics Letters, 2004, 29(15): 1730–1732.

[67] S. J. Mihailov, D. Grobnic, and C. W. Smelser, “Efficient grating writing through fibre coating with femtosecond IR radiation and phase mask,” Electronics Letters, 2007, 43(8): 442–443.

[68] M. Bernier, F. Trépanier, J. Carrier, and R. Vallée, “High mechanical strength fiber Bragg gratings made with infrared femtosecond pulses and a phase mask,” Optics Letters, 2014, 39(12): 3646–3649.

[69] C. Hnatovsky, D. Grobnic, and S. J. Mihailov, “Through-the-coating femtosecond laser inscription of very short fiber Bragg gratings for acoustic and high temperature sensing applications,” Optics Express, 2017, 25(21): 25435–25446.

[70] S. J. Mihailov, C. Hnatovsky, and D. Grobnic, “Novel type II Bragg grating structures in silica fibers using femtosecond lasers and phase Masks,” Journal of Lightwave Technology, 2019, 37(11): 2549–2556.

[71] J. Thomas, C. Voigtl-nder, D. Schimpf, F. Stutzki, E. Wikszak, J. Limpert, et al., “Continuously chirped fiber Bragg gratings by femtosecond laser structuring,” Optics Letters, 2008, 33(14): 1560–1562.

[72] C. Voigtl-nder, J. Thomas, E. Wikszak, P. Dannberg, S. Nolte, and A. Tünnermann, “Chirped fiber Bragg gratings written with ultrashort pulses and a tunable phase mask,” Optics Letters, 2009, 34(12): 1888–1890.

[73] M. Bernier, Y. Sheng, and R. Vallée, “Ultrabroadband fiber Bragg gratings written with a highly chirped phase mask and Infrared femtosecond pulses,” Optics Express, 2009, 17(5): 3285–3290.

[74] D. Grobnic, S. J. Mihailov, and C. W. Smelser, “Localized high birefringence induced in SMF-28 fiber by femtosecond IR laser exposure of the cladding,” Journal of Lightwave Technology, 2007, 25(8): 1996–2001.

[75] Q. Rong, X. Qiao, T. Guo, W. Bao, D. Su, and H. Yang, “Orientation-dependent fiber-optic accelerometer based on grating inscription over fiber cladding,” Optics Letter, 2014, 39(23): 6616–6619.

[76] L. Talbot, P. Paradis, and M. Bernier, “All-fiber laser pump reflector based on a femtosecond-written inner cladding Bragg grating,” Optics Letter, 2019, 44(20): 5033–5036.

[77] N. Abdukerim, D. C. Hnatovsky, and S. J. Mihailov, “High-temperature stable fiber Bragg gratings with ultra-strong cladding modes written using the phase mask technique and an infrared femtosecond laser,” Optics Letter, 2020, 45(2): 443–446.

[78] M. Becker, J. Bergmann, S. Brückner, M. Franke, E. Lindner, M. W. Rothhardt, et al., “Fiber Bragg grating inscription combining DUV sub-picosecond laser pulses and two-beam interferometry,” Optics Express, 2008, 16(23): 19169–19178.

[79] M. Becker, S. Brückner, M. Leich, E. Lindner, M. Rothhardt, S. Unger, et al., “Towards a monolithic fiber laser with deep UV femtosecond-induced fiber Bragg gratings,” Optics Communications, 2011, 284(24): 5770–5773.

[80] J. Fiebrandt, E. Lindner, S. Brückner, M. Becker, A. Schwuchow, M. Rothhardt, et al., “Growth characterization of fiber Bragg gratings inscribed in different rare-earth-doped fibers by UV and VIS femtosecond laser pulses,” Optics Communications, 2012, 285(24): 5157–5162.

[81] M. Leich, J. Fiebrandt, S. Jetschke, M. Rothhardt, and M. J-ger, “In situ FBG inscription during fiber laser operation,” Optics Letters, 2013, 38(5): 676–678.

[82] Y. Wang, H. Bartelt, M. Becker, S. Brueckner, J. Bergmann, J. Kobelke, et al., “Fiber Bragg grating inscription in pure-silica and Ge-doped photonic crystal fibers,” Applied Optics, 2009, 48(11): 1963–1968.

[83] M. Becker, L. Fernandes, M. Rothhardt, S. Brückner, K. Schuster, J. Kobelke, et al., “Inscription of fiber Bragg grating arrays in pure silica suspended core fibers,” IEEE Photonics Technology Letters, 2009, 21(19): 1453–1455.

[84] A. Saliminia and R. Vallée, “Fiber Bragg grating inscription based on optical filamentation of UV femtosecond laser pulses,” Optics Communications, 2014, 324(15): 245–251.

[85] Z. Zhang, B. Xu, J. He, M. Hou, W. Bao, and Y. Wang, “High-efficiency inscription of fiber Bragg grating array with high-energy nanosecond-pulsed laser Talbot interferometer,” Sensors, 2020, 20(15): 4307.

[86] M. Hou, K. Yang, J. He, X. Xu, S. Ju, K. Guo, et al., “Two-dimensional vector bending sensor based on seven-core fiber Bragg gratings,” Optics Express, 2018, 26(18): 23770–23781.

[87] A. Martinez, I. Khrushchev, and I. Bennion, “Direct inscription of Bragg gratings in coated fibers by an infrared femtosecond laser,” Optics Letters, 2006, 31(11): 1603–1605.

[88] J. Thomas, N. Jovanovic, R. G. Becker, G. D. Marshall, M. J. Withford, A. Tünnermann, et al., “Cladding mode coupling in highly localized fiber Bragg gratings: modal properties and transmission spectra,” Optics Express, 2011, 19(1): 325–341.

[89] J. Thomas, N. Jovanovic, R. G. Becker, G. D. Marshall, M. J. Withford, A. Tünnermann, et al., “Cladding mode coupling in highly localized fiber Bragg gratings II: complete vectorial analysis,” Optics Express, 2012, 20(19): 21434–21449.

[90] C. Caucheteur, T. Guo, and J. Albert, “Polarization-assisted fiber Bragg grating sensors: tutorial and review,” Journal of Lightwave Technology, 2017, 35(16): 3311–3322.

[91] P. S. Salter, M. J. Woolley, S. M. Morris, M. J. Booth, and J. A. J. Fells, “Femtosecond fiber Bragg grating fabrication with adaptive optics aberration compensation,” Optics Letters, 2018, 43(24): 5993–5996.

[92] P. Lu, S. J. Mihailov, H. Ding, D. Grobnic, R. B. Walker, and D. Coulas, “Plane-by-plane inscription of grating structures in optical fibers,” Journal of Lightwave Technology, 2017, 36(4): 926–931.

[93] P. Roldán-Varona, D. Pallarés-Aldeiturriaga, L. Rodríguez-Cobo, and J. M. López-Higuera, “Slit beam shaping technique for femtosecond laser inscription of enhanced plane-by-plane FBGs,” Journal of Lightwave Technology, 2020, 38(16): 4526–4532.

[94] A. V. Dostovalov, A. A. Wolf, A. V. Parygin, V. E. Zyubin, and S. A. Babin, “Femtosecond point-by-point inscription of Bragg gratings by drawing a coated fiber through ferrule,” Optics Express, 2016, 24(15): 16232–16237.

[95] Y. Yu, J. Shi, F. Han, W. Sun, and X. Feng, “High-precision fiber Bragg gratings inscription by infrared femtosecond laser direct-writing method assisted with image recognition,” Optics Express, 2020, 28(6): 8937–8948.

[96] K. Zhou, M. Dubov, C. Mou, L. Zhang, V. K. Mezentsev, and I. Bennion, “Line-by-Line fiber Bragg grating made by femtosecond laser,” IEEE Photonics Technology Letters, 2010, 22(16): 1190–1192.

[97] K. Chah, D. Kinet, M. Wuilpart, P. Mégret, and C. Caucheteur, “Femtosecond-laser-induced highly birefringent Bragg gratings in standard optical fiber,” Optics Letters, 2013, 38(4): 594–596.

[98] J. Luo, S, Liu, Y. Zhao, Y. Chen, K. Yang, K. Guo, et al., “Phase-shifted fiber Bragg grating modulated by a hollow cavity for measuring gas pressure,” Optics Letters, 2020, 45(2): 507–510.

[99] A. Martinez, I. Y. Khrushchev, and I. Bennion, “Thermal properties of fibre Bragg gratings inscribed point-by-point by infrared femtosecond laser,” Eletronics Letters, 2005, 41(4): 6–7.

[100] ] C. Liao, Y. Li, D. N. Wang, T. Sun, and K. T. V. Grattan, “Morphology and thermal stability of fiber Bragg gratings for sensor applications written in H2-free and H2-loaded fibers by femtosecond laser,” IEEE Sensors Journal, 2010, 10(11): 1675–1681.

[101] ] K. Cook, L. Shao, and J. Canning, “Regeneration and helium: regenerating Bragg gratings in helium-loaded germanosilicate optical fibre,” Optical Materials Express, 2012, 2(12): 1733–1742.

[102] ] J. He, Y. Wang, C. Liao, C. Wang, S. Liu, K. Yang, et al., “Negative-index gratings formed by femtosecond laser overexposure and thermal regeneration,” Scientific Report, 2016, 6: 23379.

[103] ] C. R. Liao and D. N. Wang, “Review of femtosecond laser fabricated fiber Bragg gratings for high temperature sensing,” Photonic Sensors, 2013, 3: 97–101.

[104] ] C. Wang, J. Zhang, C. Zhang, J. He, Y. Lin, W. Jin, et al., “Bragg gratings in suspended-core photonic microcells for high-temperature applications,” Journal of Lightwave Technology, 2019, 36(14): 2920–2924.

[105] ] C. Chen, X. Zhang, Y. Yu, W. Wei, Q. Guo, L. Qin, et al., “Femtosecond laser-inscribed high-order Bragg gratings in large-diameter sapphire fibers for high-temperature and strain sensing,” Journal of Lightwave Technology, 2018, 36(16): 3302–3308.

[106] ] M. Busch, W. Ecke, I. Latka, D. Fischer, R. Willsch, and H. Bartelt, “Inscription and characterization of Bragg gratings in single-crystal sapphire optical fibers for high-temperature sensor applications,” Measurement Science and Technology, 2009, 20: 115301.

[107] ] Q. Guo, Y. Yu, Z. Zheng, C. Chen, P. Wang, Z. Tian, et al., “Femtosecond laser inscribed sapphire fiber Bragg grating for high temperature and strain sensing,” IEEE Transactions on Nanotechnology, 2019, 18: 208–211.

[108] ] X. Xu, J. He, C. Liao, and Y. Wang, “Multi-layer, offset-coupled sapphire fiber Bragg gratings for high-temperature measurements,” Optics Letters, 2019, 44(17): 4211–4214.

[109] ] D. Grobnic, S. J. Mihailov, H. Ding, F. Bilodeau, and C. W. Smelser, “Single and low order mode interrogation of a multimode sapphire fiber Bragg grating sensor with tapered fibers,” Measurement Science and Technology, 2006, 17: 980–984.

[110] ] S. Yang, H. Daniel, P. Gary, and A. Wang, “Fiber Bragg grating fabricated in micro-single-crystal sapphire fiber,” Optics Letters, 2018, 43(1): 62–65.

[111] ] T. Elsmann, A. Lorenz, N. S. Yazd, T. Habisreuther, J. Dellith, and A. Schwuchow, “High temperature sensing with fiber Bragg gratings in sapphire-derived all-glass optical fibers,” Optics Express, 2014, 22(22): 26825–26833.

[112] ] S. J. Mihailov, D. Grobnic, and C. W. Smelser, “High-temperature multiparameter sensor based on sapphire fiber Bragg gratings,” Optics Letters, 2010, 35(16): 2810–2812.

[113] ] T. Habisreuther, T. Elsmann, A. Graf, and M. A. Schmidt, “High-temperature strain sensing using sapphire fibers with inscribed first-order Bragg gratings,” IEEE Photonics Journal, 2016, 8(3): 6802608.

[114] ] L. Jin, W. Jin, and J. Ju, “Directional bend sensing with a CO2-laser-inscribed long period grating in a photonic crystal fiber,’’ Journal of Lightwave Technology, 2009, 27(21): 4884–4891.

[115] ] D. Feng, X. Qiao, and J. Albert, “Off-axis ultraviolet-written fiber Bragg gratings for directional bending measurements,” Optics Letters, 2016, 41(6): 1201–1204.

[116] ] L. Shao, L. Xiong, C. Chen, A. Laronche, and J. Albert, “Directional bend sensor based on re-grown tilted fiber Bragg grating,” Journal of Lightwave Technology, 2010, 28(18): 2681–2687.

[117] ] W. Bao, Q. Rong, F. Chen, and X. Qiao, “All-fiber 3D vector displacement (bending) sensor based on an eccentric FBG,” Optics Express, 2018, 26(7): 8619–8627.

[118] ] D. Zheng, J. Madrigal, H. Chen, D. Barrera, and S. Sales, “Multicore fiber-Bragg-grating-based directional curvature sensor interrogated by a broadband source with a sinusoidal spectrum,” Optics Letters, 2017, 42(18): 3710–3713.

[119] ] W. Bao, N. Sahoo, Z. Sun, C. Wang, S. Liu, Y. Wang, et al., “Selective fiber Bragg grating inscription in four-core fiber for two-dimension vector bending sensing,” Optics Express, 2020, 28(18): 26461–26469.