Piezoelectric deformable mirror with adaptive multiplexing control

Abstract

Abstract. We describe a simple and efficient implementation of adaptive multiplexing control for high-order piezoelectric deformable mirrors. The relatively high capacitance of piezoelectric actuators allows the electrical charge to be stored in a disconnected actuator, retaining its displacement while the other actuators can be addressed. Adaptive multiplexing, consisting of selective addressing of only those actuators that need to change their elongation in the current cycle, improves the mirror performance and simplifies the driver electronics. In experiment, a 12-channel prototype of a deformable mirror with multiplexing control has been characterized. At appropriate update rates with a fixed set of control signals, the shape of the deformable mirror remains nearly constant. A surface displacement error does not exceed ϳ / 100 rms at a multiplexing frequency of 700 Hz with a full interactuator stroke of ϳ2 m. medical, 5,6 and industrial 2,5,7 applications require inexpensive, reliable, and high-quality multichannel DMs. 8 The number of channels in a DM can reach 10 2 -10 3 , especially in astronomical AO systems.1,2,4,9 Typically, each DM actuator is driven by an individual control unit, resulting in complex electronics and cabling for a high-order DM. This makes the AO system rather bulky, vulnerable to handling, and very expensive. The total cost of the driver electronics for a high-order AO system may account for two-thirds of the total system cost. 2 An attempt to simplify the DM electronics by sequential addressing of actuators was made by Kibblewhite et al. 10They built a 59-channel piezoelectric faceplate mirror that was driven by several high-voltage amplifiers ͑HVA͒ by way of 16 high-voltage switches assembled from discrete components. Due to the implementation and control complexity, this approach has not won general acceptance. In this letter, we report on the possibility of a high-order piezoelectric DM with internal multiplexing and simple driver electronics that implements adaptive addressing. This approach implies that the addressing of piezoelectric actuators is accomplished not continuously, but as needed through a pregenerated lookup table to follow the required DM figure. Only those actuators that must adjust the DM shape are addressed in each cycle. Other actuators are updated at the slowest possible rate, to keep their size. The simplicity and compactness of the multiplexing electronics allows it to be potentially integrated with the mirror, reducing the complexity of cable interconnections.In our experiment, we used a 12-channel experimental piezoelectric DM with a 25.4-mm aperture from OKO Technologies.11 The mirror uses standard 3.2-mm-diameter and 30-mm-long tubular PZT actuators ͑produced by PI Ceramic͒, positioned in a rectangular grid with 7-mm pitch. With a control voltage ranging from 0 to 300 V, the DM full stroke reaches ϳ7 m ͑hysteresis Ͻ10%͒, and its interactuator stroke, i.e., the maximum displacement between the adjacent actuators, amounts to ϳ2 m. The actuators have compa...

Adaptive optics in microscopy

“…Here a supporting structure below the reflective membrane ensures that the influence of each actuator on the DM shape is spatially more confined than for a membrane DM. Piezo-electric actuators have been employed in DMs both using direct actuation of the mirror surface (Simonov et al 2006) and through curvature control using bimorph actuators (Dainty et al 1998). Magnetically actuated DMs have also been demonstrated (Fernandez et al 2006).…”

AO SLM demonstration system and test bed

“…For that purpose, deformable mirror spatial light modulators (SLM) are of special interest. In the past, there has been a certain focus on the development of modal mirror devices employing different actuation principles, such as piezo-electric, electrostatic, or magnetic driving schemes [1][2][3]. All of them rely on the deformation of a reflective continuous face sheet in a modal manner to produce the desired surface shape.…”