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Spatial light modulator enhances signal over 10 Gbit/s

Posted: 20 Nov 2012 ?? ?Print Version ?Bookmark and Share

Keywords:optical information processing systems? antenna-on-a-chip? spatial light modulator?

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.

Dubbed, 'antenna-on- a-chip, the device is similar to those used in sensing and imaging apps. But unlike 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 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.

How it works
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 nanometre-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 by the SLM, it can be manipulated as it passes through the chip to the other side, according to Xu. The electric field between the electrodes turns the transmission on and off at very high speeds, he said.

Xu said LED screens and micromirror arrays in projectors are both SLMs in which the mirrors rotate. But although the SLM is one of the basic elements of optical systems, their switching speed is limited, he said. Some of their switching speeds can get down to microseconds, which is okay for displays and projectors, he said.

"But if you really want to do information processing, if you want to put data on each pixel, then that speed is not good enough," Xu said.


Crystalline silicon sits between two electrodes in a microscopic antenna-on-a-chip designed by researchers at Rice University. The chip, a spatial light modulator, couples with incident light and makes possible the manipulation of infrared light at very high speeds for signal processing and other optical applications. Credit: Xu Group/Rice University

According to Xu, the Rice team's device can potentially modulate a signal at more than 10 gigabits per second.

"We think this can basically scale up the capability of optical information processing systems by an order of several magnitudes," Xu said.

The researchers see potential for free-space SLMs in imaging, display, holographic, measurement and remote sensing applications.

- Dylan McGrath
??EE Times

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