Tripping the Light Fantastic
Michal Lipson pioneer photonics research
By Lauren Cahoon
Michal Lipson has a way with light. While most of us merely turn light bulbs on or off, Lipson, an associate professor in the School of Electrical and Computer Engineering, has literally bent light to her will, achieving things that seemed impossible when she first entered the field of silicon nanophotonics a decade ago. This ability to forge new paths has garnered Lipson a place of esteem and recognition in her field. She was named a MacArthur Fellow, (the “Genius Award”) in September of 2010. “When I first started, I’d give lectures on the topic, and I would always have to show a bunch of slides simply justifying the field,” says Lipson. Now, thanks in part to the work she’s done, justification for silicon photonics is no longer necessary.
|Michal Lipson in the lab with computer engineering graduate students Jacob Levy and Hugo Lira.|
Forging the Field of Silicon Photonics
Entering Lipson’s office, you’d never know that nanophotonics had once been a risky endeavor. On the fourth floor of Cornell’s Philips Hall, she has a suite of grad students working at stations outside her door, and, two floors down, a lab crammed full of humming computers and photonics equipment. Her lab is now one of hundreds around the country studying how to make light an effective messenger for computing—however, without Lipson’s work, the field may have never gotten off the ground.
“She is widely regarded as one of the most influential figures in the field of silicon photonics,” says Fan Shanhui, associate professor of electrical engineering at Stanford University. “Many of her works represent some of the first experiments that opened important directions and are almost certain to have long-lasting impacts.”
Prior to Lipson’s discoveries, silicon was an electronic-only material. Thus, all computer chips, which are made out of the element, relied on electric signaling. Electric signaling suffers from intrinsic energy loss as electrons travel along wires. Light, on the other hand, doesn’t experience the same energy drain—thus, researchers knew that light would be a much faster and efficient method for computing. But silicon was not a photon-friendly material—which was a problem; the infrastructure of the billion-dollar microelectronic industry is built for silicon.
Lipson took on the challenge, manipulating silicon so that its optical properties were amplified. After five years of hard work, her group was the first to demonstrate that silicon could be an optic material, ushering in a new field and new opportunities for science. “We made silicon into a very good optical material,” Lipson says.
“When she started here, silicon optics was considered a very risky research field,” says former ECE director Clifford Pollack, who hired Lipson to work at Cornell. “[Now] I think every engineering school in the world wishes they had hired her! She is a true visionary and leader in her field and almost everyone recognizes that.”
Lipson also recalls the time when her career path was considered dicey. “I got a lot of advice from people not to pursue this field because it was too risky,” recalls Lipson, who also joked that the field “didn’t exist” when she first started looking into silicon photonics. She admits there were times where she was tempted to follow this advice. She was also without any strong female role models. “When I started in optics, I could count the number of women in the field literally on one hand.”
She recalls how when she gave birth to her youngest son, six years ago, there was no paid maternity leave. “So I opted not to take maternity leave,” she says. “Obviously I needed to continue the research—the research didn’t stop.” While maternity rules have changed since then, Lipson says women face a more subtle set of issues today.
|Michal Lipson meets with her research group to discuss the week’s progress.|
Lipson says that the type of discrimination women now see in science and engineering is different from the overt sexism of times past. She’s dubbed it “subtle discrimination,” and describes it as sometimes subconscious, often just out of ignorance or habit due to the fact that women are a minority in these fields.
She stresses that while it’s subtle, this type of discrimination can discourage women from pursuing a career in the sciences. After an incident of subtle discrimination, “a woman might go home and feel very small, and she won’t know why,” says Lipson. “When you are young and just starting your career, this can really change your outlook.”
While she’s now in a confident place, Lipson hasn’t forgotten what it’s like to be a woman just starting in the world of science and engineering research. She has a link on her Cornell Web site that provides resources for female students and young faculty looking for advice and information on their career steps. Lipson says she has numerous women contacting her for guidance. Her main advice on subtle discrimination? Be aware of it, but don’t internalize it. “Try to brush it off,” she says.
Lipson says it took success for her to finally feel comfortable in her field. “Women are looked at under a magnifying glass,” she says. But she doesn’t view this as a bad thing. “It was just a motivator—the bar was higher.”
So Lipson stayed motivated, graduating from the Israel Institute of Technology and delving into the silicon and nanophotonics field—first as a postdoc at MIT and then on to Cornell. “I was looking for the shortest path to the highest impact,” says Lipson, “and this was definitely the path.”
Sci-Fi Experiments and Celebrity Status
This path has taken some exciting turns, harnessing photons to do things that a mere decade ago would have been billed as science fiction. For example, by sending a light beam down a silicon tube, Lipson and her group used the physical force produced by photons to move microscopic objects. Lipson also worked with mechanical engineering professor David Erickson to use this as a biological tool for moving and examining cells. Lipson has also designed a nano-fabricated material which bends light around itself, making it effectively invisible—a nanoscale cloak of invisibility. While this technology has only been used to hide very small objects, Harry Potter wannabes can take heart; “it’s not impossible [to cloak larger objects],” says Lipson. “It’s really just a technological issue.” She explains that the main roadblock is the lack of nanotech facilities designed to fabricate materials for these larger scales, but that there are people working on making it a reality.
While levitation and invisibility are exciting applications of Lipson’s research, her proudest achievement was her 2004 discovery published in the journal Nature, in which Lipson and her colleagues used nanoscopic waveguides to switch light on and off in a silicon chip. This work was followed by another Nature paper in the following year which opened up more avenues for optical silicon chips. Other researchers took notice. “Her research [in 2005] is the foundation on which researchers are currently developing large-scale optoelectronic interconnects,” says Shayan Mookherjea, an associate professor in electrical and computer engineering at the University of California, San Diego.
This work pushed the possibility of computing using optics for data transfer closer to reality. Computing using light would not only improve efficiency, but energy use as well—standard electric computer circuitry burns so much energy that large data centers like Google need to be placed near rivers for cooling. Light, Lipson says, would make them run cooler and faster. By replacing the electronic signals with photonic ones, energy use would go down while capacity would increase; bulky wires between processors would be replaced with a few streamlined optical fibers. While light-driven data centers may be the way of the future, Lipson says that the commercial industry will need to put in significant financial investment to make it happen.
Overall, it is this work in forging the information-processing capabilities of light that garnered Lipson the MacArthur award in the fall of 2010. According to the MacArthur Foundation Web site, “Lipson’s elegant solutions to a variety of theoretical and engineering challenges in silicon photonics are paving the way for the future development of practical and powerful optical computing devices.” The award recognizes something those in her field have long known. “Michal is very well respected in the engineering community,” says Amy Foster, an assistant professor of electrical and computer engineering and a past graduate student of Lipson’s. “During conferences, she is like a celebrity; you can often see other members of the community taking photos of her with their phones when she is just attending a talk or having a discussion with someone.”
Lipson’s fiancé, Alex Gaeta, a professor at Cornell’s School of Applied and Engineering Physics, says her success comes from “the ability to focus with razor precision on the essence of problems.” He adds, “She also has exceptional taste for what is the next important and interesting direction for her field.” The two are colleagues who have collaborated extensively, with more than 30 joint papers published and numerous joint grants. “I cannot imagine a more complementary collaboration with just the right merging of talents and expertise,” says Gaeta.
As for Lipson, she’s ready for the next uncharted territory. “It seems like everyone’s doing silicon photonics, it seems like maybe it’s time to leave,” she says, joking. But she’s not walking away just yet.