Sensitivity enhanced long-period grating refractive index sensor with refractive index modified cladding layer

Abstract

A sensitivity enhanced long-period grating (LPG) refractive index sensor is proposed and studied by using the LP model. In the simulation, the cladding layer of the LPG is assumed to be partially removed and then deposit a sensitivity enhancement layer (SEL) with a higher refractive index. The effects of the thickness of the original cladding material, and the thickness and refractive index of the SEL layer on the LPG transmission spectrum notch wavelength shift as a function of the ambient refractive index change are reported. The LPG sensor performance depends on the phase match condition of the core mode and cladding mode coupling in the LPG structure and the dependence of the effective index of the cladding mode on the thickness of the original cladding material, and the thickness and refractive index of the SEL layer. The structure modified cladding layer moves the work point of the long period grating to the cladding mode reorganization zone, where the cladding mode effective refractive index changes rapidly upon the LPG waveguide parameter. Proper selection of parameters of the cladding layer can be applied to enhance the modulation of the effective index of the cladding mode by the ambient refractive index through the evanescent field and thus construct sensitivity enhanced ambient refractive index sensors.