Jun 11 2018
Yale researchers have developed an innovative silicon laser that amplifies light using sound waves. A research regarding this discovery has been reported in the online edition of the journal Science.
llustration of the silicon Brillouin laser in operation. The laser is formed from nanoscale silicon structures that confine both light and sound waves. (Image credit: Yale)
In the past few years, there has been a growing interest in converting optical technologies, for example, free-space lasers and fiber optics, into very small “photonic” or optical integrated circuits. If light is used, i instead of electricity for integrated circuits, information can be sent and processed at speeds that would otherwise be impossible to achieve with traditional electronics.
According to the researchers, silicon photonics, which are optical circuits based on silicon chips, are an important platform for such technologies, because of their compatibility with current microelectronics.
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.
Peter Rakich, Associate Professor of Applied Physics at Yale
According to the team, this accelerated growth has led to an urgent requirement for innovative silicon lasers to power the new circuits - a long-standing challenge that has been difficult to overcome due to the indirect bandgap of silicon.
Silicon’s intrinsic properties, although very useful for many chip-scale optical technologies, make it extremely difficult to generate laser light using electrical current. 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.
Nils Otterstrom, First Author of the Study & Graduate student in the Rakich Lab
The light was amplified within a racetrack shape by the laser design corrals and trapped in circular motion. “The racetrack design was a key part of the innovation. In this way, we can maximize the amplification of the light and provide the feedback necessary for lasing to occur,” stated Otterstrom.
In order to achieve amplification of the light with sound, a unique structure created in the Rakich lab was used in the silicon laser. “It’s essentially a nanoscale waveguide that is designed to tightly confine both light and sound waves and maximize their interaction,” stated Rakich.
What’s unique about this waveguide is that there are 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.
Eric Kittlaus, Co-Author & Graduate Student in the Rakich Lab
The researchers explained that amplification of light with sound would not be feasible in silicon in the absence of this type of structure. “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,” stated Rakich. “Now, we’re able to use it for new types of laser technologies no one thought possible 10 years ago.”
According to Otterstrom, there are two main difficulties in building 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,” he stated. “What we observe is that while the system is clearly an optical laser, it also generates very coherent hypersonic waves.”
The researchers stated that these characteristics could prove useful in various potential applications, 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,” stated co-author 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.”