Developing ultra-sensitive optical sensors for the real-time sensing and monitoring of potential greenhouse gases such as methane and ethane is of great importance in environmental monitoring, atmospheric chemistry, healthcare sector and in petrochemical industries. Recent advances of interband cascade lasers (ICL) have played a significant role in the development of compact gas sensors with high sensitivity and low power consumption. Techniques based on laser absorption spectroscopy for trace gas sensing are advantageous, as they offer high gas specificity and sensitivity, provide fast response times and permit real-time in-situ measurements.

In this work, we report the spectroscopic detection and real-time monitoring of methane and ethane based on tunable diode laser absorption spectroscopy technique. We demonstrate a mid-infrared ICL-based gas sensor system for the detection of trace levels of methane and ethane, incorporating a wavelength modulation technique. Detection sensitivities are obtained from Allan deviation analysis, validating the stability of the system. Further, we demonstrate the simultaneous dual-gas detection capability of the system using a single excitation source, and conducted both indoor and outdoor concentration measurements. Additionally, we analyze the thermal effects of the sensor system within a wide atmospheric temperature range and a temperature compensation technique is proposed to improve the stability. This gas sensor system based on mid-infrared optical absorption spectroscopy has the merits of significantly reduced size and cost, high sensitivity, selectivity and dual-gas sensing capability.