[1] ERDOGAN T. Cladding-mode resonances in short- and long-period fiber grating filters[J]. Journal of the Optical Society of America A-optics image science and vision, 1997, 14(8):1760-1773.
[2] VENGSARKAR A M, LEMAIRE P J, JUDKINS J B, et al. Long-period fiber gratings as band-rejection filters[J]. Journal of lightwave technology, 1996, 14(1): 58-65.
[3] BHATIA V, VENGSARKAR A M. Optical fiber long-period grating sensors[J]. Optics letters, 1996, 21(9):692-694.
[4] YANG Y, CAO Y, CHEN X. A study on relation between ultra-wideband filtering characteristics and structural parameters for a chirped long-period fiber grating[J]. Indian journal of physics, 2013, 87(3): 297-302.
[5] HE T, DEMAS J, RAMACHANDRAN S. Ultra-low loss dispersion control with chirped transmissive fiber gratings[J]. Optics letters, 2017, 42(13):2531-2534.
[6] ZHANG S, GENG T, WANG S J, et al. High-sensitivity strain and temperature simultaneous measurement sensor based on multimode fiber chirped long-period grating[J]. IEEE sensors journal, 2020, 20(24): 14843-14849.
[7] ISRAELSEN S M, ROTTWITT K. Broadband higher order mode conversion using chirped microbend long period gratings[J]. Optics express, 2016, 24(21): 23969-23976.
[8] JIANG H P, GU Z T, WU J Y. Design of high sensitivity refractive index sensor based on small chirp coefficient LPFG[J]. Optical and quantum electronics, 2022, 54(6):343.
[9] ZHANG S, GENG T, NIU H W, et al. All fiber compact bending sensor with high sensitivity based on a multimode fiber embedded chirped long-period grating[J]. Optics letters, 2020, 45(15):4172-4175.
[10] YANG Y, GU Z T. Ultra-wideband filtering characteristics of chirped long-period fiber gratings with apodization optimization[J]. Acta optica sinica, 2012, 32(10): 1006006.
[11] YANG Y, GU Z T. Single-channel broadband and multichannel narrowband filtering characteristics of linear chirped long-period fiber gratings[J]. Optical engineering, 2014, 52(11):116101.
[12] FENG W, GU Z T. Ultra-broadband optical filter based on chirped long-period fiber grating and PMTP[J]. IEEE photonics technology letters, 2018, 30(15): 1361-1363.
[13] LI Z Y, GU Z T, LING Q, et al. Design of an ultra-broadband optical filter based on a local micro-structured long period fiber grating near PMTP[J]. Applied optics, 2022, 61(14):3965-3971.
[14] ZHOU W, RAN Y L, YAN Z J, et al. Sensitivity characterization of cascaded long-period grating operating near the phase-matching turning point[J]. Sensors, 2020, 20(21):5978.
[15] WU W Y, GU Z T, LING Q. High-sensitivity few-mode long-period fiber grating refractive index sensor based on mode barrier region and phase-matching turning point[J]. Optics communications, 2020, 473:125997.
[16] ZHENG Y, GUO H Y, FENG M, et al. Wavelength-tunable, ultra-broadband, biconical, long-period fiber grating mode converter based on the dual-resonance effect[J]. Sensors, 2021, 21(17):5970.
[17] REN K L, CHENG M H, REN L Y, et al. Ultra-broadband conversion of OAM mode near the dispersion turning point in helical fiber gratings[J]. OSA continuum, 2020, 3(1):77-87.
[18] KOPP V I, CHURIKOV V M, SINGER J, et al. Chiarl fiber gratings[J]. Science, 2004, 305(5680):74-75.
[19] ZHAO H, LI H P. Advances on mode-coupling theories, fabrication techniques, and applications of the helical long-period fiber gratings:a review[J]. Photonics, 2021, 8(4):106.
[20] STEGALL D B, ERDOGAN T. Leaky cladding mode propagation in long-period fiber grating devices[J]. IEEE photonics technology letters, 1999, 11(3): 343-345.
[21] MARCUSE D. Theory of dielectric optical waveguides[M]. New York:Academic Press, 1974.
[22] LU Y C, YANG L, HUANG W P, et al. Improved full-vector finite-difference complex mode solver for optical waveguides of circular symmetry[J]. Journal of lightwave technology, 2008, 26(13):1868-1876.
[23] YANG L, XUE L L, LU L Y, et al. New insight into quasi leaky mode approximations for unified coupled-mode analysis[J]. Optics express, 2010, 18(20): 20595-20609.
[24] SALUNKHE T T, LEE D J, LEE H K, et al. Enhancing temperature sensitivity of the Fabry-Perot interferometer sensor with optimization of the coating thickness of polystyrene[J]. Sensor, 2020, 20(3):794.
[25] TAKAHASHI S, SHIBATA S. Thermal variation of attenuation for optical fibers[J]. Journal of non-crystalline solids, 1979, 30(3):359-370.