How Yale scientists amplified light using sound waves on a silicon chip

A team of researchers at Yale University has figured out how to boost the intensity of light waves on a silicon microchip using sound.

Their work was published in the journal Nature Photonics.

“Silicon is the basis for practically all microchip technologies,” said team leader Peter Rakich, an assistant professor of applied physics and physics at Yale. “The ability to combine both light and sound in silicon permits us to control and process information in new ways that weren't otherwise possible.”

It has long been believed that figuring out how to precisely control the interaction of light and sound waves on a silicon chip could lead to a new, more powerful line of signal-processing technologies. 

Progress in developing this solution has been hampered because the devices created were never as efficient as they needed to be for practical applications. The Yale team was able to overcome this hurdle using new device designs that essentially prevent light and sound from escaping the circuits. 

The paper’s abstract explains the solution in a bit more technical detail:

Both Kerr and Raman nonlinearities are radically enhanced by tight optical-mode confinement in nanoscale silicon waveguides. Counterintuitively, Brillouin nonlinearities—originating from coupling between photons and acoustic phonons—are exceedingly weak in these same nonlinear waveguides. Strong Brillouin interactions have only recently been realized in a new class of optomechanical structures that control the interaction between guided photons and phonons. Despite these major advances, appreciable Brillouin-based optical amplification has yet to be observed in silicon. Using a membrane-suspended waveguide, we report large Brillouin amplification in silicon for the first time, reaching levels greater than 5 dB for modest pump powers, and demonstrate a record low (5 mW) threshold for net amplification. This work represents an important step towards the realization of high-performance Brillouin lasers and amplifiers in silicon.

“Figuring out how to shape this interaction without losing amplification was the real challenge,” explained Eric Kittlaus, a graduate student in Rakich's lab and the paper’s first author. “With precise control over the light-sound interaction, we will be able to create devices with immediate practical uses, including new types of lasers.”

In terms of some of the other practical uses that Kittlaus is referring to, the team believes fiber-optic communication and signal processing technologies will benefit greatly from this discovery. 

To learn more, read the team’s full paper, entitled Large Brillouin amplification in silicon.

Via Yale University