“Sugar Cube” NIR spectrometer

The Fraunhofer Institute for Photonic Microsystems IPMS will be presenting an extremely miniaturised, scanning grating NIR spectrometer at Photonics West, the trade show for optics technology. 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.

Dr Heinrich Grüger, who is responsible for the Sensors and Actuators Systems business unit at Fraunhofer IPMS, where the spectrometer has been developed, says: “Our new hybrid-integrated system has a volume of 2.1 cm³ only, which is about 30% 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.”

In the Fraunhofer IPMS scanning grating spectrometers, the light is diffracted on a movable optical grating built with MEMS technology. The device utilises a resonantly driving principle which enables the grating 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 was developed by Fraunhofer IPMS and measures just 9.5 × 5.3 × 0.5 mm³. The MEMS scanner featuring the diffraction grating and both optical slits is created directly on silicon wafers. A single 6″ silicon wafer is large enough for chips for hundreds of spectrometers. Applying hybrid-integration of the MEMS wafer with a spacer and an optical mirror substrate of identical size would mean that hundreds of spectrometers can be manufactured instantly. They are aligned and assembled and then separated into individual spectrometers. This means that the scientists do not have to adjust the mirrors, gratings, slits and detectors piece by piece as is required with conventional spectrometers, leading to an enormous reduction in manufacturing costs. In addition, the MEMS-based systems are distinctly more robust than conventional components.

Heinrich Grüger 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 the mini-spectrometer to the public at Photonics West in February 2013. The system, which will be demonstrated in an example application of plastics identification, performs measurements in the wavelength range from 950 nm to 1900 nm.