Optimisation and characterisation of parabolic membrane mirrors

T. Hellmuth; K. Khrennikov; W. Kronast; R. Huster; U. Mescheder

doi:10.1117/12.780758

25 April 2008 Optimisation and characterisation of parabolic membrane mirrors

T. Hellmuth, K. Khrennikov, W. Kronast, R. Huster, U. Mescheder

Proceedings Volume 6993, MEMS, MOEMS, and Micromachining III; 699305 (2008) https://doi.org/10.1117/12.780758
Event: SPIE Photonics Europe, 2008, Strasbourg, France

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.

Citation Download Citation

T. Hellmuth, K. Khrennikov, W. Kronast, R. Huster, and U. Mescheder "Optimisation and characterisation of parabolic membrane mirrors", Proc. SPIE 6993, MEMS, MOEMS, and Micromachining III, 699305 (25 April 2008); https://doi.org/10.1117/12.780758

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