Mini infrared detector fits on a chip

A team of scientists led by an Empa researcher has succeeded in developing a low-cost miniaturization process for IR spectrometers based on a quantum dot photodetector that can be integrated on a single chip.

Miniaturization
The experimental setup: A red laser was used to visualize the beam path from the fiber into the optical waveguide and the reflection from a gold mirror. The two microprobes contact the photoconductor, which has a size in the subwavelength range. Image: Empa

Researchers led by Empa researcher Ivan Shorubalko have developed a cost-effective miniaturization process for IR spectrometers based on a quantum dot photodetector. The highlight: the solution can be integrated on a single chip. Details were published in Nature Photonics.

Ultra compact design

The new spectrometer has a wide spectral bandwidth and a moderate spectral resolution of 50 cm-1 with a total active volume of the spectrometer of less than 100 by 100 by 100 micrometers. This ultra-compact design of the spectrometer allows optical-analytical measurement instruments to be integrated relatively quickly and easily into consumer electronics and space equipment.

"The monolithic integration of IR photodetectors in the subwavelength range has enormous implications for the scaling of Fourier transform waveguide spectrometers. However, our design could also be used for miniaturized Raman spectrometers, for biosensors and 'Lab-on-a-Chip'devices and for the development of high-resolution hyperspectral cameras," says Shorubalko.

Mini infrared detector fits on a chip
This is how the IR spectrometer works: The photodetector, built on a surface optical waveguide, consists of a lower gold electrode that acts as a scattering center, a photoactive layer (consisting of colloidal mercury telluride quantum dots, HgTe), and an upper gold electrode. By moving the mirror, the measured photocurrent maps the light intensity of the standing wave, i.e., the IR beam. A Fourier transform of the measured current signal then yields the optical spectrum of the beam. Image: Lars Lüder

Way for wider use

The miniaturization of infrared spectrometers is enabling wider use in consumer electronics, such as smartphones for food inspection, detection of hazardous chemicals, air pollution monitoring, and portable electronic devices. They can be used for quick and easy detection of certain chemicals without the need for laboratory equipment. In addition, they can be useful for detecting counterfeit drugs and greenhouse gases such as methane and CO2.

Source: Press release/Empa

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