Abstract

This work reports the integration of a ${{\rm Ge}_{1 - x}}{{\rm Sn}_x} {\text -} {\rm on} {\text -} {\rm AlN}$ optical waveguide (WG) on ${{\rm SiO}_2}$ substrate to facilitate mid-infrared (MIR) trace gas detection. Here, the proposed structure makes use of ${{\rm Ge}_{1 - x}}{{\rm Sn}_x}$ 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 ($\sim 90\%$) and low propagation loss of 0.61–1.18 dB/cm at $\lambda = {4.3 {-} 4.74}\;{\unicode{x00B5}{\rm m}}$ with $x = \;{6}\%$ in the ${{\rm Ge}_{1\! -\! x}}{{\rm Sn}_x}$ core. We also discuss the capability of the proposed WG to detect trace gases such as CO, ${{\rm CO}_2}$, and ${{\rm N}_2}{\rm O}$. The results show that the minimum detectable concentrations (${C_{{\rm min}}}$) of these gases are ${\sim}{0.42}$, 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.

© 2023 Optica Publishing Group

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