Specific Designed Mid-Infrared Gas Sensor Employing Bloch Surface Waves Working Near the Critical Angle

Abstract

In this paper, we theoretically design a wavelength-tunable Bloch surface waves (BSWs) platform for the illustration of SO 2 sensing in mid-infrared region, which consisted of a one-dimensional photonic crystal with an omnidirectional bandgap and an attached layer of phase change material (Ge 2 Sb 2 Te 5 , GST). Based on such configuration, the spectral response of the sensor can be actively modulated by adjusting the crystallization fraction of GST and the incident angle of light, with ultrahigh quality-factor at the order of 10 4 within a wide waveband . Such specific designed BSWs-assisted infrared gas sensor significantly enhances the molecular absorption signal by 10 6 folds. This allows us not only to qualitatively identify the species of the probed gas molecules, but also quantitatively measure the concentration of the SO 2 molecules, showing unique advantages over the conventional BSWs-based refractive index sensors working in visible and near-infrared region. It is further demonstrated that the sensor can be used for early warning of SO 2 concentration, of which the limit threshold value can reach down to 18.8 ppm when the sensor is working near the critical angle. Our work provides an alternative and effective strategy for high-performance gas sensing in the mid-infrared.

Keywords: gas sensor, Bloch surface waves, mid-infrared, wavelength-tunable, high Q-factor