Transmission resonances in silicon subwavelength grating slot waveguide with functional host material for sensing applications

TL;DR

This paper proposes a highly sensitive CO2 gas sensor using a silicon subwavelength grating slot waveguide filled with a functional material, achieving higher sensitivity through strong light confinement.

Contribution

It introduces a novel SWG slot waveguide sensor with functional material filling that enhances sensitivity compared to previous designs.

Findings

Sensitivity of 12.9 pm/ppm demonstrated in simulations

Strong light confinement in the slot improves light-matter interaction

Design can be adapted for various analytes with different functional materials

Abstract

A highly sensitive and selective CO2 gas sensor is presented based on a subwavelength grating (SWG) slot waveguide. Polyhexamethylene biguanide (PHMB) as a functional material fills the slot gap as well as the space between the silicon pillars of the SWG structure. Beyond the photonic bandgap of the SWG slot waveguide, there are transmission resonances sensitive to the refractive index changes of PHMB due to the infiltration of CO2 molecules into the functional material. The numerical simulations indicate that the sensitivity of the structure is S=12.9 pm/ppm which is considerably higher than the previously designed gas sensors based on functional materials. The higher sensitivity of the proposed sensor is attributed to the strong confinement of the light in the slot gap filled with functional material while previous designs have limited light-matter interaction by placing the functional material in the cladding. The proposed structure may be used to design various sensors by utilizing different functional material sensitive to the desired analyte.