A Cornell researcher is developing techniques for making photonic microchips—in which streams of electrons are replaced by beams of light—including ways to guide and bend light in air or a vacuum.

Michal Lipson, an assistant professor in the School of Electrical and Computer Engineering, described recent research by her Nanophotonics Group at the American Association for the Advancement of Science meeting in Seattle in February. Her talk was part of a symposium on “21st Century Photonics.” Lipson suggested that one of the first applications of nanophotonic circuits might be as routers and repeaters for fiber-optic communication systems. Such technology, she added, could speed the day when home use of fiber-optic lines becomes practical.

Researchers already have built nanoscale photonic devices in which wires are replaced by square waveguides that confine light by total internal reflection. This works only in materials with a high index of refraction, such as silicon, where there is a loss of light intensity and sometimes distortion of pulses. Lipson described a way to guide and bend light in low-index materials, including air or a vacuum. “In addition to reducing losses, this opens the door to using a wide variety of low-index materials, including polymers, which have interesting optical properties,” she said.

Connecting photonic chips to optical fibers can be a challenge because the typical fiber is vastly larger than the waveguide. It’s like connecting a garden hose to a hypodermic needle. Most researchers have used waveguides that taper from large to small, but the tapers typically have to be very long and introduce losses. Instead, Lipson’s group has made waveguides that narrow almost to a point. When light passes through the point, the waveform is deformed as if it were passing through a lens, spreading out to match the larger fiber. Conversely, the “lens” collects light from the fiber and focuses it into the waveguide. Lipson calls this coupling device “optical solder.” Based on experiments at Cornell, the device could couple 200-nanometer waveguides to 5-micron fibers with 95 percent efficiency, she reported. It also can be used to couple waveguides of different dimensions.

Some of the work has been done in collaboration with researchers working under Alexander Gaeta, Cornell associate professor of applied and engineering physics.

—Bill Steele, Cornell News Service