BU College of Engineering Magazine
Spring 2004

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Mirror, Mirror
By Jonathan Talbot

The success of Boston Micromachines Corporation (BMC) is, in large part, the success of the collaboration and friendship of two men who met in 1988 at the BU College of Engineering. Paul Bierden (ENG’92, ‘94) was an 18-year-old freshman aerospace engineering student from Rhode Island, who had followed his sister, Elizabeth Bierden, (ENG’87), a student in computer engineering, to Boston University. Tom Bifano was a newly minted Ph.D. and assistant professor, as was his wife, Mary Kate Weaver.

Weaver was Bierden’s advisor in the EK100 program, which pairs freshmen and faculty for informal weekly meetings. Bierden met Bifano through Weaver and later switched to mechanical engineering.

Three years later, Bierden regularly saw Bifano as part of their shared duty to oversee a dormitory floor of mostly freshman engineers. Bierden was a resident advisor; Bifano the faculty advisor. The two met weekly for lunch for a year at Warren Towers, with what Bierden describes as a “gaggle of freshmen engineers.” The two bonded over their weekly lunches and their efforts to mentor the younger engineers.

Second semester of his senior year, Bierden completed an independent study in the Precision Engineering Research Lab (PERL), which Bifano has led since 1990. Bierden then took what he calls “the very logical next step” to study in the master’s program at BU and to work with Bifano and PERL for another two years. “I had followed the research, and I had been talking to the graduate students,” says Bierden. “I knew it was something I could do.” He applied, was accepted, and started work on his master’s degree. Bierden finished his thesis, “Fixed Abrasive Grinding of Hard Disk Substrates,” in 1994.

A brief stint working at KAO Infosystems, a manufacturing company, took Bierden to California. Bierden and Bifano stayed in touch, and the recent graduate called his former professor when work at KAO began to diverge from Bierden’s ambition. “I was seeing where I would be in five years, and it wasn’t exciting for me,” Bierden recalls. “I had just done some high-level research and was trying to push more in that direction, and this was going to be into product.” Bierden explained that he needed a change of direction. Bifano asked his former student to join PRISM Corporation, a company he had just founded. Bierden arrived in Boston three weeks later. He’s worked here ever since.

Prism Corporation was one of the first companies incubated at the Photonics Center at Boston University. It was not, however, its most successful. Bifano founded the company in 1995, and Bierden became its only full-time employee, as chief engineer, later that year. Bifano created PRISM with BU’s help to commercialize ion machining of master stampers for CDs as an alternative to traditional wet chemistry. The new technique was five times as fast as the industry standard, half the cost, and produced no heavy metal wastes. Bierden successfully built a machine to make the master stampers. The fledgling PRISM partnered with a company in England and built some prototypes. In the end, however, the industry didn’t adopt the process. “The manufacturing process was good, but it wasn’t good enough to make them change,” recalls Bifano. PRISM closed up shop in 2000. Bierden and Bifano, however, already had their eyes on a different venture.

Undaunted by PRISM’s demise, Bierden and Bifano recognized the opportunity to commercialize another technology coming out of Bifano’s PERL group. Microelectromechanical systems (MEMS) mirror technology, developed at BU with Defense Advanced Research Projects Agency (DARPA) and Army Research Office (ARO) funding, promised to be the foundation of the next generation of adaptive optics.

The field of adaptive optics has its origins in the United States Air Force, which used the once highly secret technology to spy on Russian satellites. At its essence, adaptive optics detects the distortions in a wavefront caused by aberrations in the path (such as Earth’s atmosphere), and then alters that wavefront dynamically to compensate for the effects of those aberrations, consequently improving image resolution. The standard wavefront sensor uses an array of lenslets and a CCD camera to detect the variation between an actual wavefront and an ideal planar wavefront. While the sensing technique has been around for decades, the technology for altering the wavefront was limited to using million-dollar piezoelectric deformable mirrors, and so it remained beyond the reach of everyone but the military and astronomy communities.

“Tom came up with the idea of making a mirror that was inexpensive, that could allow this technology to get out of the million-dollar research lab,” explains Bierden, “and into the hands of people who could use it for a wide variety of applications, including vision science.” Bifano devised a way to make deformable mirrors using standard semiconductor fabrication steps, depositing and patterning subsequent layers of silicon and oxide. A chemical dipping eats away the oxides, revealing freestanding structures with gaps of about 5 microns between the mirror surface and the base. With gaps that small, voltages applied across the gaps result in electrostatic forces strong enough to narrow the gaps, pulling the mirror parts of the structure down. Different voltages applied to different parts of the multi-element mirror deform the mirror in accordance with commands from a computer based on feedback from the wavefront sensor.

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