Highly Sensitive Refractive Index Sensor Based on Mode Transition in a Dual Resonance Long Period Grating Inscribed Ridge Waveguide

Abstract

In this paper we are proposing a novel and highly sensitive refractive index sensor based on cladding mode transition in a high index coated ridge waveguide with long period grating written in its core, operating near the dispersion turning point. We have theoretically examined the phenomena of cladding mode transition in the ridge waveguide and optimized the thickness of the high index layer to obtain high refractive index sensitivity. Considering the optimized thickness and the coupling between the core mode and a suitable cladding mode, it is shown that (a) the refractive index sensitivity more than 100 μm/RIU at bio-sensing refractive index 1.33 and (b) a surface sensitivity as high as 36 nm/nm for a thin bio-layer with aqueous solution as the ambient medium can be obtained near the dispersion turning point. In addition, the refractive index sensitivity is found to vary only by 3 μm/RIU for a ±100 nm variation in the width of the ridge waveguide. The proposed device should be a promising development in the field of optical biosensors.