Numerical investigation of a Ge 1-x Sn x -on-AlN waveguide and its sensing mechanism for the detection of trace gases in the mid-infrared regime

This work reports the integration of a Ge 1− x Sn x -on-AlN optical waveguide (WG) on SiO 2 substrate to facilitate mid-infrared (MIR) trace gas detection. Here, the proposed structure makes use of Ge 1− x Sn 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 Ge 1− x Sn x core. We also discuss the capability of the proposed WG to detect trace gases such as CO, CO 2 , and N 2 O. The results show that the minimum detectable concentrations ( C min ) 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.