[1] [1] Erdogan T. Fiber grating spectra[J]. J Lightwave Technol, 1997, 15(8): 1277-1294.

[2] [2] Patrick H J, Kersey A D, Bucholtz F. Analysis of the response of long period fiber gratings to external index of refraction[J]. J Lightwave Technol, 1998, 16(9): 1606-1612.

[3] [3] Chong J H, Shum P, Haryono H, et al.. Measurements of refractive index sensitivity using long-period grating refractometer[J]. Opt Commun, 2004, 229(1): 65-69.

[4] [4] Del Villar I,Matias I R, Arregui F J, et al.. Optimization of sensitivity in long period gratings with overlay deposition[J]. Opt Express, 2005, 13(1): 56-69.

[5] [5] Del Villar I, Corres J M, Achaerandio M, et al.. Spectral evolution with incremental nanocoating of long period fiber gratings[J]. Opt Express, 2007, 14(25): 11972-11981.

[6] [6] Cusano A, Iadicicco A, Pilla P, et al.. Cladding mode reorganization in high-refractive-index-coated long-period gratings: Effects on the refractive-index sensitivity[J]. Opt Lett, 2005, 30(19): 2536-2538.

[7] [7] Cusano A, Iadicicco A, Pilla P, et al.. Mode transition in high refractive index coated long period gratings[J]. Opt Express, 2006, 14(1): 19-34.

[8] [8] Li Q S, Zhang X L, Yu Y S, et al.. Enhanced sucrose sensing sensitivity of long period fiber grating by self-assembled polyelectrolyte multilayers[J]. Reactive & Functional Polymers, 2011, 71(3): 335-339.

[9] [9] Zou F, Liu Y Q, Deng C L, et al.. Refractive index sensitivity of nano-film coated long-period fiber gratings[J]. Opt Express, 2015, 23(2): 1114-1124.

[10] [10] Coelho L, Viegas D, Santos J L, et al.. Enhanced refractive index sensing characteristics of optical fibre long period grating coated with titanium dioxide thin films[J]. Sensors & Actuators B: Chemical, 2014, 202(4): 929-934.

[11] [11] Gu Zhengtian, Lan Jinlong. Design optimization of coated long-period fiber grating based on mode transiton[J]. Chinese J Lasers, 2014, 41(1): 0105007.

[12] [12] Gu Zhengtian, Lan Jinlong. Mode transition and refractive index response in long-period fiber grating coated with double-layer overlays including metal film[J]. Acta Optica Sinica, 2014, 34(4): 0406005.

[13] [13] Jiang Xiuli, Gu Zhengtian. Impact of thin film extinction coefficient on coated long-period fiber grating transmission spectrum[J]. Acta Optica Sinica, 2010, 30(8): 2189-2195.

[14] [14] Shu X W, Huang D. Highly sensitive chemical sensor based on the measurement of the separation of dual resonant peaks in a 100-mm-period fiber grating[J]. Opt Commun, 1999, 171(s1-s3): 65-69.

[15] [15] Smietana M, Bock W J, Mikulic P, et al.. Detection of bacteria using bacteriophages as recognition elements immobilized on long-period fiber gratings[J]. Opt Express, 2011, 19(9): 7971-7978.

[16] [16] Wang Z Y, Heflin J R, Cott K V, et al.. Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings[J]. Sensors & Actuators B: Chemical, 2009, 139(2): 618-623.

[17] [17] Topliss S M, James S W, Davis F, et al.. Optical fibre long period grating based selective vapour sensing of volatile organic compounds[J]. Sensors & Actuators B: Chemical, 2010, 143(2): 629-634.

[18] [18] Chen X F, Zhou K M, Zhang L, et al.. Dual-peak long-period fiber gratings with enhanced refractive index sensitivity by finely tailored mode dispersion that uses the light cladding etching technique[J]. Appl Opt, 2007, 46(4): 451-455.

[19] [19] Corres J M, Matias I R, Del Villar I, et al.. Design of pH sensors in long-period fiber gratings using polymeric nanocoatings[J]. IEEE Sensors Journal, 2007, 7(3): 455-463.

[20] [20] Haynes W M. CRC handbook of chemistry and physics[M]. Boca Raton: CRC Press, 2012.

[21] [21] Gu Zhengtian, Zhang Jiangtao. Metal-coated long-period fiber grating liquid sensor based on dual-peak resonance[J]. Acta Optica Sinica, 2011, 31(3): 0305003.