Spectroscopy plays a pivotal role in a plethora of fields, including remote sensing, medicine, and planetary science. Many of these applications can benefit from having fully-integrated, broadband, on-chip spectrometers, but photodetectors capable of integration are less developed for certain spectral regions, such as in the mid-infrared range.
Mercury-cadmium-telluride (MCT) devices are commonly used as mid-infrared spectroscopic detectors, but cannot be integrated on-chip with frequency comb sources, which limits the advancement of compact, portable mid-infrared spectroscopy. Furthermore, the poor response of MCT devices at high frequencies limits the usage of dual-comb spectroscopy (DCS) – a powerful technique for treating broadband and high-resolution spectral information from photodetectors.
Sterczewski et al. replaced an MCT detector with a room-temperature interband cascade (IC) photodetector with gigahertz bandwidth, which provided a higher frequency response while maintaining suitable sensitivity. The authors combined the IC photodetector with two IC laser frequency combs processed from the same wafer material to build a compact, self-contained, free-running, room-temperature, DCS system for the mid-infrared.
The authors’ IC platform consumed less electrical power – a mere 2 watts – than previously-reported mid-infrared spectrometers. They tested the system by measuring difluoroethane, a heavy organic molecule employed in refrigeration, and recorded a spectrum with a bandwidth of 600 GHz centering at 3.6 µm. Their system demonstrates that the IC platform can be fully integrated as a broadband, high resolution, on-chip spectrometer in chemical sensing systems of the future.
“These findings pave the way for future monolithically-integrated spectrometers,” said author Lukasz Sterczewski. “We envision much broader future applications of compact, low-power interband cascade laser dual-comb spectrometers to molecular sensing on earth, in the atmosphere, and in space.”
Source: “Mid-infrared dual-comb spectroscopy with room-temperature bi-functional interband cascade lasers and detectors,” by L. A. Sterczewski, M. Bagheri, C. Frez, C. L. Canedy, I. Vurgaftman, and J. R. Meyer, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/1.5143954.
