Feedback stabilized deformable membrane mirrors for focus control

Sarah J. Lukes; Phillip A. Himmer; Eric J. Moog; Steven R. Shaw; David L. Dickensheets

doi:10.1117/12.812338

23 February 2009 Feedback stabilized deformable membrane mirrors for focus control

Sarah J. Lukes, Phillip A. Himmer, Eric J. Moog, Steven R. Shaw, David L. Dickensheets

Proceedings Volume 7208, MOEMS and Miniaturized Systems VIII; 72080Q (2009) https://doi.org/10.1117/12.812338
Event: SPIE MOEMS-MEMS: Micro- and Nanofabrication, 2009, San Jose, California, United States

Abstract

This paper describes a method to extend the range of motion of a deformable, continuous membrane mirror beyond the limit of open-loop electrostatic instability through the use of a feedback control scheme. The feedback scheme is based on capacitive sensing of the mirror. The sensing is achieved by coupling the actuation electrodes to a ring oscillator. We use a differential technique, where the frequency of the coupled oscillator is compared to a reference ring oscillator. Analysis of the system using a simplified parallel-plate model shows that the range of stable deflection depends on the dynamics of the device and control circuitry, and suggests that stable full-gap displacement can be achieved under certain conditions. Experimental results are provided, showing stable closed-loop deflection of our silicon nitride test device to 61% of the air gap, consistent with the predictions of our model.

Citation Download Citation

Sarah J. Lukes, Phillip A. Himmer, Eric J. Moog, Steven R. Shaw, and David L. Dickensheets "Feedback stabilized deformable membrane mirrors for focus control", Proc. SPIE 7208, MOEMS and Miniaturized Systems VIII, 72080Q (23 February 2009); https://doi.org/10.1117/12.812338

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KEYWORDS

Mirrors

Capacitance

Feedback control

Actuators

Control systems

Oscillators

Silicon

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