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Fraunhofer set to unveil sugar cube-sized spectrometer

Posted: 21 Jan 2013 ?? ?Print Version ?Bookmark and Share

Keywords:near-infrared spectrometer? Photonics West? sugar cube? MEMS scanner? plastics identification?

An extremely miniaturized near-infrared spectrometer (NIR) will be presented by Fraunhofer Institute for Photonic Microsystems IPMS during the Photonics West conference. This device enables analysis of gaseous, liquid and solid materials immediately on site instead of taking samples for lab analysis. The optical bench is smaller than a sugar cube and thus it might fit into mobile devices as well as in automated process analysis tools.

While today's market does offer many spectrometers for lab use, there are few systems for simple on-location measurements. There are two major reasons for this: First most of these instruments use one or two dimensional photodiode arrays of III-V semiconductors like indium-gallium-arsenide, which inflate costs, and second they are voluminous for technological reasons. With miniaturized grating spectrometers this will change, says Dr. Heinrich Grger, who is responsible for the "Sensors and Actuators Systems" business unit at Fraunhofer IPMS, where the spectrometer has been developed. "Our new hybrid-integrated system has a volume of 2.1 cm3 only, which is about 30 percent smaller than a common sugar cube. Due to its small outline and low power consumption of only a few milliwatts, it is ideal for integration into mobile measurement instruments and in situ measurements in facilities and buildings."

Fraunhofer's NIR spectrometer

NIR spectrometer. Light is diffracted on a movable optical grating realized in a MEMS technology.

With the scanning grating spectrometers developed by Fraunhofer IPMS, the light is diffracted on a movable optical grating realized in a MEMS technology. The device uses a resonantly driving principle of the grating which enables to scan a spectrum with a single highly sensitive detector instead of an array arrangement. The central element of the spectrometer is a MEMS chip which has been developed by Fraunhofer IPMS and measures just mm3. The MEMS scanner featuring the diffraction grating and both optical slits is directly manufactured on silicon wafers. A single 6 inch silicon wafer is large enough for chips for hundreds of spectrometers on it. Applying hybrid-integration of the MEMS wafer with a spacer and an optical mirror substrate of identical size means that hundreds of spectrometers can be manufactured instantly. They are aligned and assembled and then separated into individual spectrometers. This means that the scientists don't have to adjust the mirrors, gratings, slits and detectors piece by piece like required with conventional spectrometers.

Heinrich Grger estimates that it will be about three to five years before the system will be ready for introduction to the market. Nevertheless, he and his team will be presenting the first fully functional model of this mini-spectrometer to the broad public at Photonics West in February 2013. The system, which will be demonstrated in an application example of plastics identification, performs measurements in the wavelength range from 950 nm to 1900 nm. This spectral range opens interesting applications for organic compound evaluation as for example portable analysis instruments for the food industry, mobile medical and pharmaceutical analysis instruments, in situ quality testing or warning and monitoring systems for security or facility management applications.

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