SILICON MICROMACHINING - Adaptive optics approach commercial applications

DENVER, CO-Silicon micromachining technology has reduced the cost of adaptive optical mirror systems by two orders of magnitude, but there are still one or two orders of magnitude to go before the devices de scend from the realm of research to routine industrial use, according to an invited speaker at the 44th annual meeting of the International Society for Optical Engineering (SPIE) held here in July.

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DENVER, CO-Silicon micromachining technology has reduced the cost of adaptive optical mirror systems by two orders of magnitude, but there are still one or two orders of magnitude to go before the devices de scend from the realm of research to routine industrial use, according to an invited speaker at the 44th annual meeting of the International Society for Optical Engineering (SPIE) held here in July.

Adaptive optical mirror systems made with conventional piezoelectric technology cost about $100,000 apiece, according to Gleb Vdovin, an assistant professor at Delft University of Tech nology (Delft, the Netherlands). But that price is only reasonable for builders of large astronomically priced telescope systems or the classified military uses for which adaptive optics were originally developed in both Russia and the USA three decades ago.

"There are no [industrial] applications for that," Vdovin said. "Because if you want to place such an adaptive mirror in every laser printer, there's no way."

Potentially large and lucrative commercial applications in areas such as industrial lasers, medicine, and telecommunications call for much-lower prices, said Vdovin, whose invited talk led a two-day series of presentations on wavefront-control methods, devices, and applications. Bulk micromachining has enabled him to devise a $2000 system that has found widespread applications in the USA and Europe during the past 2.5 years, Vdovin said. Thomas Bifano followed Vdovin's talk with a description of a $5000 surface-micromachining system under development at Boston University that further broadens the potential range of nonresearch applications and may eventually be produced even more cheaply than the bulk method.


FIGURE 1. Section of bulk-micromachined adaptive optic device shows modally controlled mirror suspended by spacers over bias control for electric field.
Click here to enlarge image

The $2000 devices are produced through batch processing and fabrication at a one-man company, OKO Technologies (Delft, the Netherlands), in which Vdovin, the only employee, works one day a week after spending four days at the university. About 100 mirrors and 40 mirror systems (that include controlling electronics) have been sold to US customers during the past 2.5 years, and many more have been distributed to European companies through a $35 million Micro-Optical Silicon Systems (MOSIS) program, funded by the European Community for development of European industry.

The OKO bulk method produces devices by working on a wafer scale (see Fig. 1). "You etch through the wafer and get a deformable membrane that can be quite large," Vdovin said. "We can make mirrors up to 50 mm in diameter, which means that you can use them with telescopes and high-powered lasers."


Section of surface-micromachined adaptive optic device shows three actuators in zonal deformable mirror attached by posts to an array of such parallel-plate electrostatic actuators.
Click here to enlarge image

The surface-micromachining method under development at Boston University creates devices on the surface of silicon chips in a manner similar to fabrication of electronics (see Fig. 2). Instead of a single deformable membrane controlled by an electric field, the BU device relies upon an array of electrostatic actuators. "Electrostatic actuation holds considerable promise for membrane mirror shape control because it offers nearly reversible (low power) actuation, no hysteresis, several microns of stroke, and nanometer-scale precision and repeatability," Bifano said.

While the OKO system is more directed toward conventional applications of adaptive optics, the BU system could be packaged in a manner similar to a photodiode for applications in which a very small mirror (1 or 2 mm, for instance) is needed with numerous channels of control. "For instance, if you have a very small laser beam and you want to do something with it, Bifano's approach is much better because of the potential to achieve a high [density of] spatial deformation," Vdovin said. "And potentially I think Bifano's method may be cheaper because it uses less wafer surface. But the application principle is different."

Actually moving these technologies from the research arena and into a commercial price range will require an interest by large companies that can benefit from technologies of scale by deploying the technology in huge applications, Vdovin said. "I can't do anything about that because I would need to be a huge company, like Lucent [for instance]. If Lucent does it, we'll get adaptive optics at a very cheap price very soon."

Hassaun Jones-Bey

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