Mid-infrared tunable quantum cascade lasers for gas-sensing applications

The quantum cascade (QC) laser does not involve the material bandgap for the generation of light. Therefore, InP- and GaAs-based III-V semiconductor materials can now be used for the generation of long-wavelength, mid-infrared light. These materials are also straightforward to process and pattern. This is essential for the more sophisticated device geometries such as distributed feedback (DFB) lasers. DFB lasers provide a very elegant and reliable method to achieve a well-defined single-wavelength emission (called single-mode operation) as opposed to the usually multiple-mode emission of free-running Fabry-Perot resonators. QC-DFB lasers were first demonstrated in 1996. They have evolved very rapidly and have already shown great promise in many different gas-sensing applications.