Nonlinear gas sensing based on third-harmonic generation in cascaded chalcogenide microfibers

Abstract

The performance of conventional gas sensors based on light absorption in the mid-infrared (MIR) faces the challenges of the high cost and low efficiency of photodetection at these wavelengths. In this paper, a nonlinear gas sensor based on third-harmonic generation (THG) in cascaded chalcogenide microfibers is proposed. In the first microfiber section, the input MIR light with “fingerprint” frequency has shown the ability for a large amount of gas absorption. The second microfiber section is used for THG pumped by the residual MIR light. In this process, the sensing signal is converted to the near-infrared region, and the power variation caused by the absorption is amplified due to the nonlinear relation between pump and harmonic signals. According to our analysis, the lowest methane concentration of 7.4×10−8 can be detected at a practically drawable Ae2Se3 microfiber length of 1\xa0cm. Compared to direct MIR gas sensing, cascaded microfiber sensing has the advantages of improved sensing performance and also shorter absorption length.