Ultra-broadband optical filter based on chirped long-period fiber grating using leaky mode coupling

Abstract

An ultra-broadband optical filter was proposed and demonstrated based on leaky mode coupling in a coated chirped long-period fiber grating (CLPFG). The CLPFG was coated with a material whose refractive index (RI) was higher than that of the fiber cladding, enabling the coupling of the core mode to leaky modes, to achieve a desired coupling efficiency. Complex coupled-mode theory was used to investigate the power evolution of the core mode that resulted from the coupling. From this, the conditions in which the core mode power attenuates the most rapidly were identified. In addition, phase matching turning point (PMTP) was used in the design, to overcome the conflict between the range of grating period change and the grating length in the CLPFG. Finally, an optimized CLPFG-based filter with a length of 3.5 cm was obtained, which has a symmetrical attenuation band with an operating bandwidth over 300 nm. Within the operating bandwidth, the flatness is less than 2.5 dB and the transmittance is lower than 0.1%.

References

[1] ErdoganT. 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] VengsarkarA M, LemaireP J, JudkinsJ B, et al.. Long-period fiber gratings as band-rejection filters[J]. Journal of lightwave technology, 1996, 14(1):58-65

[3] BhatiaV, VengsarkarA M. Optical fiber long-period grating sensors[J]. Optics letters, 1996, 21(9):692-694

[4] YangY, CaoY, ChenX. 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] HeT, DemasJ, RamachandranS. Ultra-low loss dispersion control with chirped transmissive fiber gratings[J]. Optics letters, 2017, 42(13):2531-2534

[6] ZhangS, GengT, WangS 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] IsraelsenS M, RottwittK. Broadband higher order mode conversion using chirped microbend long period gratings[J]. Optics express, 2016, 24(21):23969-23976

[8] JiangH P, GuZ T, WuJ Y. Design of high sensitivity refractive index sensor based on small chirp coefficient LPFG[J]. Optical and quantum electronics, 2022, 54(6):343

[9] ZhangS, GengT, NiuH 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] YangY, GuZ T. Ultra-wideband filtering characteristics of chirped long-period fiber gratings with apodization optimization[J]. Acta optica sinica, 2012, 32(10):1006006

[11] YangY, GuZ T. Single-channel broadband and multichannel narrowband filtering characteristics of linear chirped long-period fiber gratings[J]. Optical engineering, 2014, 52(11): 116101

[12] FengW, GuZ 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] LiZ Y, GuZ T, LingQ, 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] ZhouW, RanY L, YanZ J, et al.. Sensitivity characterization of cascaded long-period grating operating near the phase-matching turning point[J]. Sensors, 2020, 20(21):5978

[15] WuW Y, GuZ T, LingQ. 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] ZhengY, GuoH Y, FengM, 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] RenK L, ChengM H, RenL 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] KoppV I, ChurikovV M, SingerJ, et al.. Chiarl fiber gratings[J]. Science, 2004, 305(5680):74-75

[19] ZhaoH, LiH 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] StegallD B, ErdoganT. Leaky cladding mode propagation in long-period fiber grating devices[J]. IEEE photonics technology letters, 1999, 11(3): 343-345

[21] MarcuseD. Theory of dielectric optical wave-guides[M], 1974, New York, Academic Press

[22] LuY C, YangL, HuangW 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] YangL, XueL L, LuL Y, et al.. New insight into quasi leaky mode approximations for unified coupled-mode analysis[J]. Optics express, 2010, 18(20):20595-20609

[24] SalunkheT T, LeeD J, LeeH 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] TakahashiS, ShibataS. Thermal variation of attenuation for optical fibers[J]. Journal of non-crystalline solids, 1979, 30(3): 359-370