System Bits: Dec. 29

Optoelectronics built using existing manufacturing
Using only processes found in existing microchip fabrication facilities, researchers at MIT, the University of California at Berkeley, and the University of Colorado have produced a working optoelectronic microprocessor that computes electronically but uses light to move information.

The researchers reminded that optical communications promise to reduce chips’ power consumption — desirable in its own right but also essential to maintaining the steady increases in computing power we’ve come to expect.

This development should make optical communication more attractive to the computer industry, on one hand. On the other, it makes an already daunting engineering challenge even more difficult.

New physics and new designs must be used to figure out how to take ingredients and process recipes that are used to make transistors, and use those to make photodetectors, light modulators, waveguides, optical filters, and optical interfaces, explained MIT professor of electrical engineering Rajeev Ram, referring to the optical components necessary to encode data onto different wavelengths of light, transmit it across a chip, and then decode it.

Researchers have produced a working optoelectronic chip that computes electronically but uses light to move information. The chip has 850 optical components and 70 million transistors, which, while significantly less than the billion-odd transistors of a typical microprocessor, is enough to demonstrate all the functionality that a commercial optical chip would require.
(Source: MIT)

The project began as a collaboration between Ram, Vladimir Stojanović, and Krste Asanovic, who were then on the MIT Department of Electrical Engineering and Computer Science faculty. Stojanović and Asanovic have since moved to Berkeley, and they, Ram, and Miloš A. Popović, who was a graduate student and postdoc at MIT before becoming an assistant professor of electrical engineering at Colorado, are the senior authors on a paper that describes the new chip.

They’re joined by 19 co-authors, eight of whom were at MIT when the work was done, including two of the four first authors: graduate students Chen Sun and Jason Orcutt, who has since joined IBM’s T. J. Watson Research Center.

The chip has 850 optical components and 70 million transistors, which, while significantly less than the billion-odd transistors of a typical microprocessor, is enough to demonstrate all the functionality that a commercial optical chip would require.

Turning a smartphone into a 3D scanners with an algorithm
In an advance that could help make high-quality 3D scanning cheaper and more readily available, Brown University researchers have created an algorithm that helps turn smartphones and off-the-shelf digital cameras into structured light 3D scanners.

The lab of Gabriel Taubin, associate professor of engineering and computer science has been focusing on getting 3D image capture from relatively low-cost components because the 3D scanners on the market today are either very expensive or are unable to do high-resolution image capture, so they can’t be used for applications where details are important.

Unsynchronized structured light: Structured light scanning normally requires a projector and camera to be synchronized. A new technique eliminates the need for synchronization, which makes it possible to do structured light scanning with a smartphone.
(Source: Taubin Lab/Brown University)

Most high-quality 3D scanners capture images using a technique known as structured light. A projector casts a series of light patterns on an object, while a camera captures images of the object. The ways in which those patterns deform over and around an object can be used to render a 3D image. But for the technique to work, the pattern projector and the camera have to be precisely synchronized, which requires specialized and expensive hardware.

The Brown University-developed algorithm enables the structured light technique to be done without synchronization between projector and camera, which means an off-the-shelf camera can be used with an untethered structured light flash. The camera just needs to have the ability to capture uncompressed images in burst mode (several successive frames per second), which many DSLR cameras and smartphones can do.

Metal films make displays more affordable, efficient
According to Penn State researchers, a new material that is both highly transparent and electrically conductive could make large screen displays, smart windows and even touch screens and solar cells more affordable and efficient.

Indium tin oxide, the transparent conductor that is currently used for more than 90 percent of the display market, has been the dominant material for the past 60 years, the team reminded, but in the last decade, the price of indium has increased dramatically resulting in displays and touchscreen modules becoming a main cost driver in smartphones and tablets, given that they make up close to 40 percent of the cost. While memory chips and processors get cheaper, displays get more expensive from generation to generation. Manufacturers have searched for a possible ITO replacement, but until now, nothing has matched ITO’s combination of optical transparency, electrical conductivity and ease of fabrication.

The Penn State team approached these issues from a different angle. The researchers use thin — 10 nm — films of an unusual class of materials called correlated metals in which the electrons flow like a liquid. While in most conventional metals, such as copper, gold, aluminum or silver, electrons flow like a gas, in correlated metals, such as strontium vanadate and calcium vanadate, they move like a liquid. According to the researchers, this electron flow produces high optical transparency along with high metal-like conductivity.

A figure showing the crystal structure of strontium vanadate(orange) and calcium vanadate (blue). The red dots are oxygen atoms arranged in 8 octohedra surrounding a single strontium or calcium atom. Vanadium atoms can be seen inside each octahedron. 
(Source: Penn State)

In other words, they are trying to make metals transparent by changing the effective mass of their electrons. They are doing this by choosing materials in which the electrostatic interaction between negatively charged electrons is very large compared to their kinetic energy. As a result of this strong electron correlation effect, electrons ‘feel’ each other and behave like a liquid rather than a gas of non-interacting particles. This electron liquid is still highly conductive, but when you shine light on it, it becomes less reflective, thus much more transparent.