Optimization of a fiber grating film sensor based on dual peak resonance

Based on the dual peak resonance of long-period fider grating(LPFG),a novel film sensor is presented.in which films sensitive to the surrounding gases are coated on the cladding of the fiber grating region,and the intervals of the dual peak resonant wavelengths change with the film refractive index.According to the coupled-mode theory,a triple-clad numerical model is developed to analyze the relation between the sensitivity S and the thin film optical parameters(the film thickness h3 and the refractive index n3and the fiber grating parameters (the grating period A and the coreindex modulation (o)).By using optimization method,the optimal film optical parameters and the grating structure parameters are obtained.Numerical simulation shows that the sensitivity of this scheme to refractive index of the films is predicted to be more than 10-7.The theomtic analysis provides straightforward foundation for the aetual highly sensitive fdm sensors.