Unimorph mirror for adaptive optics in space telescopes

Abstract

This paper presents a unimorph deformable mirror intended to be used as secondary corrector in space telescopes. The deformable mirror consists of a single-crystal silicon wafer (76.2 mm diameter, 500 μm thickness) covered with an optical coating on the front side and an array of 25 independent piezoelectric transducer (PZT) actuators acting in d mode on the back side. The mirror is mounted on an isostatic support with three position linear actuators controlling the rigid-body motion. The first part of the paper presents the experimental results obtained with the manufactured prototype. The mirror was tested in terms of root mean square (RMS) wavefront error, open-loop long-term stability, voltage budget for active control, rigid-body actuation, reflectivity, and dynamic response. The prototype is fully compliant with the requirements set by the European Space Agency (ESA). The second part of the paper, purely based on numerical simulations, presents a robust way to face thermal distortion, inherent to unimorph architecture.

Damping of piezoelectric space instruments: application to an active optics deformable mirror

“…The optimal inductor and resistor are computed according to Eqs. (4,5). The shunt reduces the peak response of the mirror by a factor 10 (or 23 dB); this is possible thanks to the…”

“…More recently, the space community has been interested in extending the use of deformable mirrors in space telescopes to compensate for aberrations induced by deployment imprecision, manufacturing errors, gravity release and thermal distortion. Thanks to its simple architecture, the piezoelectric unimorph technology can offer high reliability; hence it is a good candidate for space applications as shown in [3,4].…”

“…The proposed concept is demonstrated on a deformable mirror we developed in the framework of a GSTP program ("BIALOM") on behalf of the European Space Agency (ESA) [7]. The performance of the mirror has already been extensively presented in [4]. It has been shown that the mirror is already fully compliant with all the goals sets by ESA (from mechanical and optical point of view), corresponding to a Technology Readiness Level of 4 (TRL 4).…”

Electromechanical Vibration Characteristics of Porous Bimorph and Unimorph Doubly Curved Panels

“…Therefore, having the properties of porous materials, a combination of porous structures with piezoelectric layers leads to smart porous systems, with controllable characters and, consequently, with unique applications in industry. Piezoelectric bimorphs and unimorphs are also hugely used in mechatronic systems such as vibration piezoelectric energy harvesters [15][16][17][18][19][20], piezoelectric transducers [21], mechatronic handling devices [22], adaptive optics in space telescopes [23][24][25], damping systems [26,27], and continues monitoring systems [28,29]. Hence, analyzing the dynamic characteristics of piezoelectric coupled structures may help to design efficient mechatronic systems.…”

Thermal Balance and Active Damping of a Piezoelectric Deformable Mirror for Adaptive Optics

“…In a recent paper [4], the passive and active damping augmentation of piezoelectric DMs was investigated. The passive damping was achieved by providing the front side of the DM, outside the pupil, with a ring of piezoelectric ceramic (PZT) [5] used simultaneously to reduce the thermal sensitivity of the mirror and to provide passive shunt damping of the critical mode at f 1 by connecting it to an appropriate, properly tuned R-L circuit [6]. Alternatively, a strategy for active damping was also proposed, where the wavefront sensor array, a Shack-Hartmann (SH) in this case, and the shape control actuators (the PZT array on the back of the DM) are used to construct modal filters and introduce active damping in the critical mode(s).…”