A high-sensitivity metal-coated long-period fiber grating(LPFG) sensor based on material dispersion is designed.Based on the coupled mode theory,the influence of the material dispersion on the dual-peak characteristics of the metal-coated LPFG is studied.After considering the material dispersion,the jumping region of the dual-resonant-wavelength shifts toward the thinner film thickness,and the sensitivity of the dual-peak metal-coated LPFG sensor to liquid refractive index(RI) can be obtained to supply accurate parameter combinations.Experimentally,two kinds of silver-coated LPFGs with different film thicknesses and grating periods are fabricated to monitor the salt solution,and the sensitivities of these two sensors are compared.The experimental results are consistent with the theoretical analyses.
The design of a tunable metal-coated long-period fiber grating (LPFG) filter based on the material dispersion consideration is presented. The tuning of the resonant wavelength can be achieved by heating the metal layer. Based on the coupled mode theory, the influences of the material dispersion on the transmission spectrum of the metalcoated LPFG are studied. There is a special grating period for a specific cladding mode; when the grating period is less than or equal to the special grating period, the material dispersion has weak influence on the resonant wavelength. Under such condition, the attenuation band depth corresponding to the specific cladding mode has excellent stability while the temperature changes, thus improving the filtering performances of the tunable loss filter. Further, experimental results demonstrate the validity and feasibility of the proposed tunable filter.
