Technology and applications of micromachined adaptive mirrors

Abstract

The end of the cold war and the introduction of military technologies to the market has created new application fields for many originally military technologies. One of these technologies is adaptive optics, dealing with dynamic control of the quality of an optical system. As for almost any technology 'imported' from the military research field, adaptive optics is expensive. Fortunately there are many civil applications for adaptive optics which produce the necessary development thrust.Expensive adaptive optics are acceptable for applications where specialized custom-made systems are needed. In the past, and even now, designers of large ground-based telescopes costing in excess of tens of millions of dollars could afford expensive, specially designed high-quality adaptive systems to improve image quality. The extension of adaptive optics into the field of less expensive scientific equipment such as low-end professional telescopes, industrial lasers and optical information processing systems will only be possible after reduction of the fabrication costs by a few orders of magnitude. The functionality and quality of devices and systems must be preserved or even improved during the transition described.The market sector for serially-produced scientific equipment, industrial laser systems and components, information processing equipment such as CD player optical pickups, amateur telescopes, optical communication systems and displays is comparable to the aforementioned high-end military and scientific sectors. To deal with the large volume demand, serial or even mass-production technologies should be used for the fabrication of adaptive optics. The problem of high system quality at low cost can be solved using silicon micromachining.Various optical micromachined devices have been demonstrated in the past twenty years, among them micromachined adaptive mirrors. Silicon-based microfabrication in its present state forms the technological foundation for inexpensive implementation of complete adaptive optical systems, as it allows for cheap fabrication of CCD-based wavefront sensors, control computers and wavefront correctors in the framework of a uniformly inexpensive technology.

Design of large deflection electrostatic actuators

“…Parallel plate actuators are used for many applications, including force rebalance in accelerometers [13] [14] [15], deformable optics [16], relays, and valves [17] [18]. Generally, these parallel-plate actuators have very limited range (usually 1/3 of the starting gap), and have to be feedback-controlled to achieve useful response.…”

Adaptive aberration correction in a confocal microscope

“…This simple implementation involves little more than the inclusion of an adaptive correction element in standard confocal microscope hardware. For the purposes of aberration correction and the application of the bias aberrations, we elected to use a membrane mirror (OKO Technologies, Delft, The Netherlands) that consisted of an aluminized silicon nitride membrane positioned above an electrode structure of 37 hexagonal electrodes (18,19). The shape of the membrane mirror is controlled by the appli- cation of voltages to the electrode structure.…”

Materials, effects and components for tunable micro‐optics

“…The idea behind wave front correction is to apply the inverse of this phase deformation using a deformable mirror and thereby improve the optical quality of the image. Commercially available deformable membrane mirror devices (DMMDs) are usually made of silicon [6,7], the most common material in the area of microsystem technology processing. The disadvantage is the high stiffness of silicon: for electrostatic actuation, the high stiffness leads to a high value of the required driving voltage of several 100 V.…”