Real-time and non-destructive hydrocarbon gas sensing using mid-infrared integrated photonic circuits

A chip-scale mid-infrared (mid-IR) sensor was developed for hydrocarbon gas detection. The sensor consisted of amorphous Si (a-Si) optical ridge waveguides that were fabricated by complementary metal-oxide-semiconductor (CMOS) processes. The waveguide exhibited a sharp fundamental mode through lambda = 2.70 to 3.50 mu m. Its sensing performance was characterized by measuring methane and acetylene. From the spectral mode attenuation, the characteristic C-H absorption bands associated with methane and acetylene were found at lambda = 3.29-3.33 mu m and lambda = 3.00-3.06 mu m, respectively. In addition, real-time methane and acetylene concentration monitoring was demonstrated at lambda = 3.02 and 3.32 mu m. Hence, the mid-IR waveguide sensor enabled an accurate and instantaneous analysis of hydrocarbon gas mixtures.