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Antenna on a Chip Zips Through 3-D ‘Free Space’

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HOUSTON, Nov. 21, 2012 — A new micron-scale spatial light modulator (SLM) works in 3-D “free space” and runs orders of magnitude faster than those used in sensing and imaging devices, and it holds great potential for imaging, display, holographic, measurement and remote sensing applications.

The “antenna on a chip” device, developed at Rice University, looks like a tiny washboard and could make current commercial products used to manipulate infrared light obsolete.

A new antenna on a chip for spatial light modulation enables the manipulation of infrared light at very high speeds for signal processing and other optical applications.
A new antenna on a chip for spatial light modulation enables the manipulation of infrared light at very high speeds for signal processing and other optical applications. From left, graduate students Ciyuan Qiu, Jianbo Chen and Yang Xia, and Qianfan Xu, an assistant professor of electrical and computer engineering. Courtesy of Jeff Fitlow/Rice University.

Light manipulation is central to the information economy, from light-reflecting compact discs and their video variants to lasers used for sensing, security and surgery. Light carries data through optical fibers for telecommunications and signals on the molecular scale as photonics techniques improve. LEDs power TV displays and are even replacing incandescent lightbulbs in homes.

But in the realm of computers, light has been constrained by 2-D circuitry, tied to waveguides that move it from here to there, said Qianfan Xu, an electrical and computer engineering assistant professor at Rice and leader of the research. The investigators believe that 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 SLM chips are nanoscale ribs of crystalline silicon that form a cavity 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.

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

Such 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. The electric field between the electrodes turns the transmission on and off at very high speeds.

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Individual SLMs can be likened to pixels, and Xu sees the potential for manufacturing chips containing millions of them. With conventional integrated photonics, he said, “you have an array of pixels, and you can change the transmission of each pixel at a very high speed. 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 of the other side.

“LED screens are spatial light modulators; so are micromirror arrays in projectors, in which the mirrors rotate. Each pixel changes the intensity of light, and you see an image. So an SLM is one of the basic elements of optical systems, but their switching speed is limited; some get down to microseconds, which is OK for displays and projection.”

But if you want to put data on each pixel for information processing, the speed is not good enough. The device could potentially modulate a signal at more than 10 Gb/s, he said.

The design of the antenna on a chip for spatial light modulation.
The design of the antenna on a chip for spatial light modulation. The chip can process incident infrared light for signal processing at very high speeds. Courtesy of Xu Group/Rice University.

“With this device, we can make very large arrays with high yield,” he said. “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.”

For example, the device could give the single-pixel camera in development at Rice — which at the beginning took eight hours to process an image — the ability to handle real-time video.

“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 said. “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.”

Although these antennas would not be suited for general computing, they could perform optical processing tasks comparable in power to supercomputers.

“Optical information processing is not very hot,” Xu said. “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.”

Details of the antenna appear in Scientific Reports (doi:10.1038/srep00855).  

For more information, visit: www.rice.edu

Published: November 2012
Glossary
cavity
In a laser, the optical resonator formed by two coaxial mirrors, one totally and one partially reflective, positioned so that laser oscillations occur.
holography
Holography is a technique used to capture and reconstruct three-dimensional images using the principles of interference and diffraction of light. Unlike conventional photography, which records only the intensity of light, holography records both the intensity and phase information of light waves scattered from an object. This allows the faithful reproduction of the object's three-dimensional structure, including its depth, shape, and texture. The process of holography typically involves the...
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
remote sensing
Remote sensing is a method of data collection and observation where information about objects, areas, or phenomena on Earth's surface is gathered from a distance, typically using sensors onboard satellites, aircraft, drones, or other platforms. This technique enables the monitoring and analysis of Earth's surface and atmosphere without direct physical contact. Remote sensing systems capture electromagnetic radiation (such as visible light, infrared, microwave, or radio waves) reflected or...
spatial light modulator
A spatial light modulator (SLM) is an optical device that modulates or manipulates the amplitude, phase, or polarization of light in two dimensions, typically in the form of an array. SLMs are versatile tools used in various optical applications, including adaptive optics, optical signal processing, holography, and imaging. There are different types of SLMs, each with its own operating principle: Liquid crystal spatial light modulators (LC-SLM): These SLMs use liquid crystal technology to...
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