Development of high-efficient NIR-scanning gratings for spectroscopic applications

Abstract

In recent years, Micro Opto Electro Mechanical Systems (MOEMS) have been reached more and more importance in technical applications. This is caused by the increased reliability of micro systems combined with the reduction of costs by high volume production. In this paper, we will present a resonant scanning grating chip with high diffraction efficiency, developed for the NIR region (900 - 2500 nm), which is based on our resonant micro scanning mirror. The grating was additionally applied to the silicon mirror plate by a chemical wet etch process. Therefore, three different fabrication technologies have been developed, showing high efficiencies in the first diffraction order. Compared to investigations with direct structured gratings in the reflective aluminium surface, gratings with up to 714 lines/mm could be fabricated combined with an improved process parameter control. These new resonant driven scanning gratings are still compatible to the scanning mirror fabrication process. They have a large surface of 3x3 mm² and resonant frequencies of down to 150 Hz, which results in a lower demand on the bandwidth of the electronic read out, when applied to a spectrometer set-up. The maximum mechanically scan angle of the grating mirror plate could be increased to +/- 12° at a driving voltage of 36 V. First measurement results and an improved design of a micro spectrometer, working with only one single InGaAs-Detector in a spectral range of 900 to 2500 nm will be presented and discussed.