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ETH researchers fabricate a mini-spectrometer smaller than a coin

Researchers from ETH Zurich have devised a compact infrared spectrometer. Its size is small enough to fit on a computer chip, and the new development will open up new possibilities, both in space and in everyday life. David Pohl and Marc Reig Escalé, belonging to the group headed by Rachel Grange, Professor, Optical Nanomaterials, Department of Physics, teamed up with other colleagues to develop a chip with a size of nearly 2 square centimeters in size, and using the chip they could analyze infrared light similar to when they would do it with a conventional spectrometer.

A conventional spectrometer separates the incident light into two paths,  which is reflected off two mirrors. The reflected light beams are then reassembled and measured using a photodetector. When one of the mirrors is moved, it creates an interference pattern that can be inspected to determine the proportion of different wavelengths in the incoming signal, and since chemical substances create characteristic gaps in the infrared spectrum, the researchers can utilize the resulting patterns to identify which substances occur in the test sample, along with its concentration. The same principle underlies the mini-spectrometer fabricated by the ETH scientists, although, in the new device, the incident light is analyzed using special waveguides with an optical refractive index that can be adjusted externally through an electric field. Escalé says that the spectrometer can measure not only infrared light but also measure visible light, subject to the proper configuration. Unlike other integrated spectrometers that can cover only a narrow range of the light spectrum, the device created by Grange’s group has a major advantage, as it can easily analyze a wide section of the spectrum.

Apart from it being compact, the ETH device provides two other advantages, viz., the ‘spectrometer on a chip’ only has to be calibrated once, compared to traditional devices that need to be recalibrated repeatedly, and as it contains no moving parts, it does not demand a lot of maintenance. The ETH researchers used a material that is used as a modulator for telecommunication applications, which can restrict the light to the inside. The device still needs a lot of improvement before it can be integrated into electronic devices.


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