PROCEEDINGS ARTICLE | March 13, 2013
Proc. SPIE. 8616, MOEMS and Miniaturized Systems XII
KEYWORDS: Microelectromechanical systems, Diffraction, Mirrors, Cameras, Electrodes, Silicon, Micromirrors, Microfabrication, Semiconducting wafers, Diffraction gratings
Programmable MEMS diffraction gratings are used for spectroscopic applications because of their potential in tailoring visible and infrared spectra. A fully programmable MEMS diffraction grating (FPMDG), where every micro-mirror can move independently in a range 0 - λ/2, where λ is the wavelength of light, leads to a better control of the intensity for each wavelength in the synthetized spectrum – the intensity can take any value from 0 (micro-mirror λ/4-condition) to the maximum (no micro-mirror displacement). The FPMDG chip contains 64 micro-mirrors which are actuated electrostatically. Rigid Si micro-mirrors are connected to side electrodes via linkage arms, permitting the micro-mirror to follow a pure vertical displacement, reducing the micro-mirror bending throughout actuation. Microfabrication is based on a 4 mask photolithography process, using SOI and Pyrex wafers. Each micro-mirror of the FPMDG chip can move by 1.25μm at voltages below 100 V. Two families of micro-mirrors, 50μm or 80μm wide, show negligible cross-talk during actuation. The micro-mirror bowing is as small as 0.14 μm over 700 μm and remains unchanged throughout actuation. Extinction ratios of up to 100 have been achieved by actuating only 3 adjacent micro-mirrors. The measurements have shown high stability and good reproducibility over time. Finally, FPMDGs are used to demonstrate shaping of the input spectrum: the intensity in a particular wavelength region is controlled through independent actuation of a set of adjacent micro-mirrors. The result is attenuation or cancellation of the corresponding wavelengths.
