19 Nov 2012

US researchers develop 3D antenna-on-a-chip

Researchers at Rice University, US, have fabricated a micron-scale spatial light modulator (SLM) with the potential to run orders of magnitude faster than today's devices .

Unlike other devices in two-dimensional semiconducting chips, the chips work in three-dimensional "free space."

As lead researcher Professor Qianfan Xu from electrical and computer engineering highlights, 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."

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

The SLM chips are nano-scale 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 infra-red light passes through silicon, but once captured by the SLM, it can be manipulated as it passes through the chip to the other side. The electric field between the electrodes turns the transmission on and off at very high speeds.

Individual SLMs are analogous to pixels, and Xu sees the possibility of manufacturing chips that contain millions of them.

What's more, the researcher says his team's device can potentially modulate a signal at more than 10 gigabits per second.

"What we show here is very different from what people have been doing," he says. "With this device, we can make very large arrays with high yield. Our device is based on silicon and can be fabricated in a commercial CMOS factory, and it can run at very high speed. We think this can basically scale up the capability of optical information processing systems by an order of several magnitudes."

As an example, he suggested the device could give a single-pixel camera, also under development at Rice University, the ability to handle real-time video. At the beginning this took eight hours to process an image.

"Or you could have an array of a million pixels, and essentially have a million channels of data throughput in your system, with all this signal processing in parallel," he adds. "If each pixel only runs at kilohertz speeds, you don't get much of an advantage compared with microelectronic systems. But if each pixel is working at the gigahertz level, it's a different story."

Though Xu's antennas would not be suitable for general computing, he said, they could be capable of optical processing tasks that are comparable in power to supercomputers.

"Optical information processing is not very hot," he admits. "It's not fast-developing right now like plasmonics, nanophotonics, those areas. But I hope our device can put some excitement back into that field."

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