Recent progress in infrared absorption spectroscopy for on-chip waveguide gas sensing

The on-chip gas sensors possess advantages, such as miniaturization, portability, low power, and no need for optical path calibration. These benefits enhance the applications of these sensors, such as mobile monitoring and portable instrumentation. In recent years, waveguide gas sensing detection techniques based on infrared absorption spectroscopy (IAS) have been extensively studied, which is covered from theory to experiment and from discrete components to integrated systems. Overall, on-chip gas sensing plays a crucial role in various fields, such as environmental protection, industrial control, and medical diagnosis, facilitating high-precision and high-sensitivity gas concentration monitoring. This article summarizes the research progress of waveguide gas sensing based on IAS in the past decade. This review concludes the fundamental principles of waveguide gas sensing based on IAS and various gas sensing methods and discusses the applications, advantages, and limitations of different waveguides which are composed of different materials and structures in gas sensing. In addition, this article presents various waveguide coupling methods and strategies for enhancing the evanescent field to improve interaction with gas analytes. Finally, we give an outlook on the application of IAS-based waveguide gas sensors.