Photonic-Phononic Waveguides Used to Create Brillouin Laser

A laser that uses sound waves to amplify light could help address the need for silicon lasers that can overcome obstacles associated with silicon’s indirect bandgap when powering photonic integrated circuits.

The laser design, created by a research team at Yale University, corrals amplified light within a racetrack shape to trap the light in a circular motion. The suspended silicon waveguide racetrack structure stimulates the nonlinear effect of Brillouin scattering to achieve lasing from silicon.

Silicon Brillouin laser in operation. The laser is formed from nanoscale silicon structures that confine both light and sound waves. Courtesy of Yale University.

To amplify the light with sound, the laser uses a special structure developed by researchers that causes it to enter a dynamic regime, in which phonon linewidth narrowing is produced through optical self-oscillation. The structure is “essentially a nanoscale waveguide that is designed to tightly confine both light and sound waves and maximize their interaction,” said Peter Rakich, associate professor at Yale, who led the research.

The waveguide has two distinct channels for light to propagate. “This allows us to shape the light-sound coupling in a way that permits remarkably robust and flexible laser designs,” said researcher Eric Kittlaus.

Amplification of light using sound would not be possible without this type of structure, said researchers. To create a laser that uses a combination of light and sound waves to amplify light on a chip, researchers had to design and fabricate a device where the amplification outpaced the loss, and they had to understand these counterintuitive dynamics.

“What we observe is that while the system is clearly an optical laser, it also generates very coherent hypersonic waves,” said researcher Nils Otterstrom. Results of the research could provide a platform to develop silicon-based optoelectronic circuits and devices, leading to potential applications ranging from integrated oscillators to new schemes for encoding and decoding information.

“Using silicon, we can create a multitude of laser designs, each with unique dynamics and potential applications," said Ryan Behunin, an assistant professor at Northern Arizona University and a former member of the Rakich lab. "These new capabilities dramatically expand our ability to control and shape light in silicon photonic circuits.”

The research was published in Science (doi:10.1126/science.aar6113).