'Antenna-on-a-chip' speeds infrared light transmission

November 21, 2012 // By Dylan McGrath
Researchers at Rice University have developed a micron-scale spatial light modulator (SLM) that they say has the potential to improve the capability of optical information processing systems by several orders of magnitude.

The Rice "antenna on a chip" is similar to those used in sensing and imaging devices. But inlike other devices in two-dimensional semiconducting chips, the Rice chips work in three-dimensional "free space."

According to Qianfan Xu, an assistant professor of electrical and computer engineering at Rice, the SLM chip differs dramatically from current state of the art technology.

"With this device, we can make very large arrays with high yield," Xu said. "Our device is based on silicon and can be fabricated in a commercial CMOS factory, and it can run at very high speed."

Xu and his Rice colleagues detailed their antenna-on-a-chip for light modulation this week in Nature's open-access, online journal Scientific Reports.

Xu said the antennas would not be suitable for general computing, but could be used for optical processing tasks that are comparable in power to supercomputers.

In today's computers, light is confined to two-dimensional circuitry, tied to waveguides that move it from here to there, Xu said. In the paper, Xu and his colleagues maintain 2-D systems fail to take advantage of "the massive multiplexing capability of optics" made possible by the fact that "multiple light beams can propagate in the same space without affecting each other."

Conventional integrated photonics relies on an array of pixels, the transmission of which can be changed at very high speed, Wu said. "When you put that in the path of an optical beam, you can change either the intensity or the phase of the light that comes out the other side," he said.

The Rice SLM chips are essentially nanoscale ribs of crystalline silicon that form a cavity sitting between positively and negatively doped silicon slabs connected to metallic electrodes. The positions of the ribs are subject to nanometer-scale "perturbations" and tune the resonating cavity to couple with incident light outside.

That coupling pulls incident light into the cavity. Only infrared light passes through silicon, but once captured