Extreme miniaturization of infrared (IR) detectors is critical for their integration into next-generation consumer electronics, wearables and ultra-small satellites. To date, however, IR detectors have relied on bulky, high-cost materials and technologies. The trend toward ultracompact designs is supported by the development of a cost-effective miniaturization process for IR spectrometers based on a quantum dot photodetector, which can be integrated on a single chip.

The proof-of-concept miniaturized Fourier-transform waveguide spectrometer incorporates a subwavelength photodetector as a light sensor, consisting of colloidal mercury telluride quantum dot and compatible with complementary metal-oxide-semiconductor technology. This achievement by researchers from Massachusetts Institute of Technology, ETH Zurich (Switzerland), Swiss Federal Laboratories for Materials Science and Technology (Empa), Universidad de Salamanca (Spain) and Ecole Polytechnique Fédérale de Lausanne (Switzerland) is reported in Nature Photonics.

Waveguide spectrometer with a monolithically integrated photoconductor and the respective cross sections. Source: Nat. Photon. (2022). https://doi.org/10.1038/s41566-022-01088-7

The resulting spectrometer exhibits a large spectral bandwidth and moderate spectral resolution of 50 cm⁻¹ at a total active spectrometer volume below 100 μm × 100 μm × 100 μm. This ultra-compact spectrometer design allows the integration of optical-analytical measurement instruments into consumer electronics and space devices.

"The monolithic integration of subwavelength IR photodetectors has a tremendous effect on the scaling of Fourier-transform waveguide spectrometers," said Empa researcher Ivan Shorubalko. "But this may also be of great interest for miniaturized Raman spectrometers, biosensors and lab-on-a-chip devices as well as the development of high-resolution snapshot hyperspectral cameras."