Sensitivity analysis of a square shape apodize fibre Bragg grating chemical sensor assisted by high refractive index bi-directional coupler on both sides

Special featured Fibre Bragg grating has a great potential to meet the demand of development of highly sensitive optical fibre technology based chemical sensors working in harsh environment. Fibre Bragg grating assisted in between directional coupler could be significantly tuned the power coupling efficiency between two high refractive index layers. In this paper standard si-based FBG has been fabricated with square shape of apodization profile based on Cu-vapour laser and second harmonics generation based technique. Then FBG has been incorporated in between two high refractive index material followed by substrate in either side with low refractive index sensing layer. Finite difference method (FDM) based MATLAB program has been developed to extract the TE/TM modes supported by this proposed composite planar waveguide structure. Sensitivity has been calculated by b − λ graph technique for both angular/wavelength interrogation cases.