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Proceedings Paper

Optimisation and characterisation of parabolic membrane mirrors
Author(s): T. Hellmuth; K. Khrennikov; W. Kronast; R. Huster; U. Mescheder
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Paper Abstract

MOEMS-based thin silicon membrane mirrors with a useable diameter of 5mm and fast (up to 1kHz) tunable focal length (80 mm to 1m) have been realized. A ring shaped counter electrode is used to achieve a parabolic membrane deformation by electrostatic forces. A circular kerf at the outer perimeter of the membrane provides a soft suspension to the rim and thus reduces the needed driving voltage. FEM has been used for optimisation of the design, especially of the soft suspension, which is realized by a controlled thinning of the outer rim of the Si-membrane. A critical issue for demanding applications is the membrane distortion induced by material stress and the fabrication process. Membrane residual stress reduction has been obtained by using SOI-technology (c-silicon) and by optimisation of the Al deposition process (Al-coated Si-membrane). For dynamic tests of the optical mirror properties a stroboscopic interferometer has been realized. A pulsed laser diode with a pulse duration of 10μs is used as a light source which is synchronized with the modulated electrical field driving the membrane mirror. The interference pattern is recorded with a CCD and evaluated with conventional phaseshift techniques. The geometry is similar to a Mach-Zehnder interferometer. The reference path length can be varied with a piezoceramic to induce the phase shift.

Paper Details

Date Published: 25 April 2008
PDF: 11 pages
Proc. SPIE 6993, MEMS, MOEMS, and Micromachining III, 699305 (25 April 2008); doi: 10.1117/12.780758
Show Author Affiliations
T. Hellmuth, Hochschule Aalen (Germany)
K. Khrennikov, Hochschule Aalen (Germany)
W. Kronast, Fachhochschule Furtwangen (Germany)
R. Huster, Fachhochschule Furtwangen (Germany)
U. Mescheder, Fachhochschule Furtwangen (Germany)

Published in SPIE Proceedings Vol. 6993:
MEMS, MOEMS, and Micromachining III
Hakan Urey, Editor(s)

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