Electrostatic micro-deformable mirror for adaptive optics

摘要

Next generation adaptive optical (AO) systems require deformable mirrors with very challenging parameters, up to 250 000 actuators and inter-actuator spacing around 500μm. MOEMS-based devices are promising for the development of a complete generation of new deformable mirrors. We are currently developing a micro-deformable mirror (MDM) based on an array of electrostatic actuators with attachments to a continuous mirror on top. The originality of our approach lies in the elaboration of layers made of polymer materials. Mirrors with very efficient planarization and active actuators have been demonstrated, with a piston motion of 2μm for 30V. Using our dedicated characterization bench, we have measured a 6.5kHz resonance frequency, well suited for AO applications. Based on the design of this actuator and our polymer process, realization of a complete polymer-MDM is under way. The electrostatic force provides a non-linear actuation, while AO systems are based on linear matrices operations. Then, we have developed a dedicated 14-bit electronics in order to "linearize" the actuation. After calibrating the behavior of each actuator and fitting the curve by a sixth order polynomial, the electronics delivers a linearized output. The response is nearly perfect over our 3x3 MDM prototype with a standard deviation of 3.5 nm, and we have then obtained the influence function of the central actuator. First evaluation on the cross non-linarities has also been evaluated on the OKO mirror and a simple look-up table is sufficient for determining the location of each actuator whatever the locations of the neighbor actuators. Electrostatic MDM are particularly well suited for AO applications.