MEMS optical grating aims at medium infrared range

A scanning grating spectrometer operating in the medium infrared range from 3µ to 12µ wavelength is under development at the Fraunhofer Institute for Photonic Microsystems IPMS. This region covers characteristic absorption lines of many chemical substances that are significant for security monitoring.

Therefore, the motivation for the research is to create a compact mobile sensor that can quickly detect and quantify these materials.

Fraunhofer is working with 17 other companies in the MIRIFISENS project to achieve this. The project began in September 2012 and runs for 42 months. The total budget is about $14.6 million, of which the European taxpayer will provide about $10 million.

At the core of the MIRIFISENS project Mid Infrared Innovative Lasers for Improved Sensing of Hazardous Substances is a miniaturized quantum cascade laser (QCL), which is being developed by researchers of the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg. The QCL covers a large range of the wavelengths that are important for the spectroscopic fingerprint in the medium infrared range.

To set the light of the QCL to the defined wavelengths, scientists at Fraunhofer IPMS developed a highly reflective diffraction grating acts as the quantum cascade laser's variable frequency external resonator. It allows for the tuning of laser wavelengths with a frequency of 1kHz, with a variable frequency range of up to 20 per cent of the central wavelength.

QCL module with integrated MEMS diffraction grating. (Source: Fraunhofer IAF)

"Electrostatically-driven MEMS grating mirrors are much more compact than galvanometer scanners, make almost no sound and allow for very high scanning frequencies due to their low weight. In combination with miniaturised laser sources, they are ideal for integration into mobile handy sensor systems, simple measurements on location and for integration into industrial measurement technology at production and processing facilities," said Fraunhofer IPMS' project manager Jan Grahmann.

Grahmann is due to present a paper on the grating at the Photonics West conference in San Francisco, which is held from Feb. 7 to 12, 2015. The paper is titled, "Large MEMS diffraction grating results providing an EC-QCL wavelength scan of per cent." A prototype grating will also be exhibited at the Photonics West exhibition, which takes place Feb. 10 to 12.

- Peter Clarke
  EE Times Europe