New silicon laser makes silicon ‘sing’

A new type of silicon laser that uses sound waves to amplify light. 

Illustration of the silicon Brillouin laser in operation. The laser is formed from nanoscale silicon structures that confine both light and sound waves.
Illustration of the silicon Brillouin laser in operation. The laser is formed from nanoscale silicon structures that confine both light and sound waves.

In recent years, there has been increasing interest in translating optical technologies at speed into tiny optical or “photonic” integrated circuit using light. This would be impossible with conventional electronics.

Silicon photonics — optical circuits based on silicon chips — are one of the leading platforms for such technologies, thanks to their compatibility with existing microelectronics.

Now, Yale scientists have devised a new type of silicon laser that uses sound waves to amplify light.

Peter Rakich, an associate professor of applied physics at Yale who led the research said, “We’ve seen an explosion of growth in silicon photonic technologies the past few of years. Not only are we beginning to see these technologies enter commercial products that help our data centers run flawlessly, we also are discovering new photonic devices and technologies that could be transformative for everything from biosensing to quantum information on a chip. It’s really an exciting time for the field.”

Nils Otterstrom, a graduate student in the Rakich lab and the study’s first author said, “This rapid growth has created a pressing need for new silicon lasers to power the new circuits — a problem that has been historically difficult due to silicon’s indirect bandgap. It’s a problem that’s stymied scientists for more than a decade. To circumvent this issue, we need to find other methods to amplify light on a chip. In our case, we use a combination of light and sound waves.”

The silicon laser uses a special structure i.e., a nanoscale waveguide that’s is designed to tightly confine both light and sound waves and maximize their interaction. The fascinating property of this waveguide is there are two distinct channels for light to propagate. This allows shaping the light-sound coupling in a way that permits remarkably robust and flexible laser designs.

Rakich said, Without this type of structure, the researchers explained, amplification of light using sound would not be possible in silicon. We’ve taken light-sound interactions that were virtually absent in these optical circuits, and have transformed them into the strongest amplification mechanism in silicon. Now, we’re able to use it for new types of laser technologies no one thought possible 10 years ago.”

Otterstrom said, “The laser design corrals amplified light within a racetrack shape — trapping it in a circular motion.”

“There were two main challenges in developing the new laser: First, designing and fabricating a device where the amplification outpaces the loss and then figuring out the counter-intuitive dynamics of this system. What we observe is that while the system is clearly an optical laser, it also generates very coherent hypersonic waves.”

According to scientists, these properties may lead to a number of potential applications ranging from integrated oscillators to new schemes for encoding and decoding information. In addition, capabilities dramatically expand the ability to control and shape light in silicon photonic circuits.

A study about the discovery appears in the online edition of the journal Science.