Sound waves used to boost intensity of light on a silicon chip
Using a newly-developed waveguide, scientists at Yale have created a method to significantly increase the power of laser light on a silicon chip by boosting it with sound waves. The researchers believe that this new device could have practical uses in commercial technologies, including more efficient fiber-optic communications and better data signal processing.
According to the researchers, amplifying light signals directly on a silicon chip is the realization of a goal sought for many years by researchers worldwide who looked to build such hybrid technologies, but were held back by light amplification efficiencies that were below a level acceptable for real-world applications. The Yale scientists claim to have solved this problem by producing a device that actively prevents light and sound from escaping while being amplified.
"Silicon is the basis for practically all microchip technologies," said Peter Rakich, assistant professor of applied 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."
The new device takes advantage of what is known as Brillouin amplification, where laser light is "pumped" into one end of the waveguide in the opposite direction of the incoming light signal. This generates sound waves as acoustic phonons (vibrational motion energy in which molecules uniformly oscillate at a single frequency).
The sound waves then mechanically scatter the pumped laser light, thereby allowing the incoming light signal to stimulate the emission of so many more photons that an overwhelming avalanche of incoming photons is created. This continued high-throughput of photons is then maintained by the sound signals which drive the frequency information forward to the end of the waveguide where it is emitted as a greatly-amplified light signal.
"Figuring out how to shape this interaction without losing amplification was the real challenge," said Eric Kittlaus, a graduate student at Yale and part of Rakich's team. "With precise control over the light-sound interaction, we will be able to create devices with immediate practical uses, including new types of lasers."
Developed as an element of research in a five-year program supported by DARPA, the Rakich lab has concentrated on creating new, light-based integrated circuit technologies and components, and the researchers ardently believe that this latest device developed in their program would be suitable for a range of practical and commercial applications in a number of areas.
"We're glad to help advance these new technologies, and are very excited to see what the future holds," said Heedeuk Shin, a former member of the Rakich lab, now a professor at the Pohang University of Science and Technology in Korea.
The results of this research were recently published in the journal Nature Photonics.