Numerical investigation of a Ge1-xSnx-on-AlN waveguide and its sensing mechanism for the detection of trace gases in the mid-infrared regime

Abstract

This work reports the integration of a Ge1−xSn x -on-AlN optical waveguide (WG) on SiO2 substrate to facilitate mid-infrared (MIR) trace gas detection. Here, the proposed structure makes use of Ge1−xSn x in the core of the WG and the AlN cladding; this enables the effective guidance and confinement of a broad spectrum of MIR light waves within the GeSn WG. The gas detection mechanism of the device is based on the evanescent wave field component of a guided mode to examine particular molecular absorption/trace gas characteristics of the upper cladding environment. The designed WGs exhibit high power confinement (∼90%) and low propagation loss of 0.61–1.18 dB/cm at λ=4.3−4.74µm with x=6% in the Ge1−xSn x core. We also discuss the capability of the proposed WG to detect trace gases such as CO, CO2, and N2O. The results show that the minimum detectable concentrations (Cmin) of these gases are ∼0.42, 0.12, and 0.16 ppm, respectively, for x=6%. These encouraging results enable a new sensor platform for GeSn-based MIR trace/atmospheric gas detection.