Zurich Federal Institute of Technology successfully develops compact infrared spectrometer

[ Instrument Network Instrument Development ] Researchers at the ETH Zurich Institute of Technology developed a compact infrared spectrometer. It is small enough to be integrated on a single computer chip, but its performance can still open up many interesting possibilities for space and everyday applications.

Today, smartphones can do almost everything: take photos or videos, send messages, determine current location, and video calls. With the versatile compact infrared spectrometer developed by ETH researchers, our smartphones can even determine the alcohol content of a beer or the maturity of a fruit.

At first glance, using a smartphone for chemical analysis seems like a bold idea. Because infrared spectrometers that currently perform such chemical analysis typically weigh from a few kilograms to tens of kilograms, it is difficult to integrate them into handheld devices. According to Mamms Consulting, the research team led by Rachel Grange, professor of optical nanomaterials at the Department of Physics at the Federal Institute of Technology in Zurich, is now taking an important step towards this vision. David Pohl and Marc Reig Escale? collaborated with other colleagues to develop a The chip is only about 2 square centimeters in size. With this chip, they can analyze infrared light like a traditional spectrometer.

Waveguide replacement mirror

The incident light of a conventional spectrometer is separated by a spectroscopic system in a certain space before being reflected by the mirror, and then the reflected beams are recombined and measured by a photodetector. Moving one of the mirrors produces an interference pattern, and the interference pattern can be used to determine the ratio of different wavelengths in the incident light. Because each chemical has its unique infrared signature absorption, scientists can use the resulting map to identify the substances and concentrations present in the test sample.

The micro spectrometer developed by ETH researchers also uses the same principle. However, in the devices they developed, the movable mirror was no longer used to analyze the incident light. They used a special waveguide that can adjust the optical refractive index by an external electric field. Pohl explains: “The change in refractive index has a similar effect to moving mirrors, so this design allows us to separate the incident spectrum in the same way.”

Challenging structured process

Depending on the configuration of the waveguide, the researchers can detect different parts of the spectrum. "In theory, as long as the waveguide is properly configured, our miniature spectrometer can measure not only infrared light but also visible light," Escalé said. Compared to other integrated spectrometers that cover only a narrow spectral range, the devices developed by the Grange team have significant advantages because they facilitate wide spectrum analysis.

In addition to its small size, ETH physicist innovation has two other advantages: this "on-chip spectrometer" only needs to be calibrated once compared to conventional equipment that requires constant recalibration; in addition, since it does not contain any Moving parts are therefore more durable and require less maintenance.

ETH researchers use a material in this on-chip spectrometer that is also used as a modulator in the telecommunications industry. This material has many positive properties, but as a waveguide it limits light to the inside. This disadvantage makes it less than ideal because measurements can only be made if part of the guided light can be emitted. To this end, scientists have designed a fine metal structure to connect to the waveguide to scatter light outside the device. Grange explained: “It takes a lot of work in the clean room to construct the material in the way we need it.”

Perfect for space applications

However, the actual integration of such a miniature spectrometer into a mobile device or other electronic device still requires some technical improvements. Grange said: "At the moment, we also need to use external sensors to measure the signal. Therefore, if we want to build a complete compact device, we need to integrate the corresponding detector."

Initially, the researchers' target application was not chemical analysis, but for completely different applications - astronomical research, infrared spectrometers can provide important information about distant objects. Since the Earth's atmosphere absorbs a large amount of infrared light, it is necessary to place these instruments on satellites or telescopes in space. This compact, lightweight and stable miniature spectrometer is clearly relatively economical when shipped to space and naturally has great advantages.