In a recent issue of Nature magazine, Cornell researchers presented a new development in the area of silicon photonics: a completely optically controlled silicon switch. With an experimental diameter of approximately 10 micrometers, the switch is turned on and off by beams of light termed control beams.
Traditionally, communication interfaces have been composed of electrical switches that convert incoming optical data into an electrical current for switch operations. The result is a net slowing of data transmission across these interfaces. Because an all-optical switch skips the conversion process, it “has the potential to be significantly faster than it’s electrical counterpart,” stated article coauthor Prof. Robert R. Panepucci, Florida International University, in an email.
The switch’s experimental design relies primarily on an optical resonator ring, a circular device adept at propagating beams of light at certain wavelengths in a circular path. Usually, the ring is placed tangent to a straight optical conductor that carries the light beam to be routed.
As light travels past the ring, “it is scattered into the ring … and if it is the right wavelength it travels around many times,” said Prof. Michal Lipson, electrical and computer engineering, also co-author of the article. The circumference of the ring must be such that there “is an integer number of half a wave length in the ring,” Lipson added.
A second straight optical conductor culminates at the ring and provides a path for the control beam. When a control beam of nearly the same wavelength interacts with the silicon, it forces electrons to be absorbed changing the ring’s index of refraction. And “that changes the filtering properties of the ring,” Lipson said.
“Every time you want to switch it either on or off, you need to send another pulse of light that changes the index of refraction,” Lipson explained.
In addition to speed, the silicon all-optical switch offers other benefits to electrical engineering.
“The advantage here is that it is done on silicon,” Lipson said. “Because there is an incredible amount of infrastructure invested on silicon-billions of dollars spent-the industry wants to keep working with silicon,” he added.
Until now, however, silicon has rarely been used to control light, except over fixed optical paths. “Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon, but the flow of light in these structures is predetermined and cannot be readily modulated during operation,” said the researchers in their paper.
In fact, much of the work that has been done on silicon in the area of photonics has involved large oddly shaped high-powered devices that are too large for application in electronics.
The experimental design achieved a size small enough to be “used for telecommunication between fibers,” Lipson said. Further miniaturization of the current model is still possible to only a few microns, he assured, but not to the point of making them a viable alternative to electrical interfaces in computer circuitry.
“Ultimately, reducing the device will require a change in geometries, as ring resonators less than two-three [micro]meters do not confine light so effectively,” Panepucci explained.
Currently the power consumption of the all-optical silicon switch is slightly less compared to other optical devices, “but it still requires more power than an electronic transistor for example,” Lipson said.
Nonetheless, “the ultimate power consumption of these devices has not been thoroughly investigated, but it needs to be considered to enable high levels of integration and functionality,” Panepucci said.
Archived article by David Andrade
Sun Staff Writer