Hybrid Fibre Grating Structure of an Optical Fibre Refractive Index Sensor

The refractive index which is compensated with temperature by incorporating an LPG and FBG has been established and evaluated in a series configuration. As refractive index is used by Long Period Grating which allows it to be responsive to external refractive index difference ,for temperature compensation the Fibre Bragg Grating was used. For efficient interpretation of both refractive index and temperature the Long Period Grating (LPG) and Fibre Bragg Grating (FBG) wavelengths were chosen to be within suitable spectral bandwidths. For the use as a chemical sensor the hybrid sensor performance was rated by varying sodium chloride (NaCl) concentrations in temperature from 11-96 oC and water from 0.25 – 2 %NaCl and by recording its related attenuation band shifts. The hybrid sensor to NaCl concentration and temperature sensitivity is found to be 0.62 nm/%NaCl and 9 pm/oC respectively.