My watch list
my.chemeurope.com  
Login  

Engineers give optical switches the 'contrast' of electronic transistors

02-Feb-2018

Sajal Dhara

Ritesh Agarwal's research on photonic computing has been focused on finding the right combination and physical configuration of materials that can amplify and mix light waves in ways that are analogous to electronic computer components. In a paper published in Nature Communications, he and his colleagues have taken an important step: precisely controlling the mixing of optical signals via tailored electric fields, and obtaining outputs with a near perfect contrast and extremely large on/off ratios. Those properties are key to the creation of a working optical transistor.

Current computer systems represent bits of information, the 1's and 0's of binary code, with electricity. Circuit elements, such as transistors, operate on these electric signals, producing outputs that are dependent on their inputs.

As fast and powerful as computers have become, Ritesh Agarwal, professor in the Department of Materials Science and Engineering in the University of Pennsylvania's School of Engineering and Applied Science, knows they could be more powerful. The field of photonic computing aims to achieve that goal by using light as the medium.

Agarwal's research on photonic computing has been focused on finding the right combination and physical configuration of materials that can amplify and mix light waves in ways that are analogous to electronic computer components.

He and his colleagues have taken an important step: precisely controlling the mixing of optical signals via tailored electric fields, and obtaining outputs with a near perfect contrast and extremely large on/off ratios. Those properties are key to the creation of a working optical transistor.

"Currently, to compute '5+7,' we need to send an electrical signal for '5' and an electrical signal for '7,' and the transistor does the mixing to produce an electrical signal for '12,'" Agarwal said. "One of the hurdles in doing this with light is that materials that are able to mix optical signals also tend to have very strong background signals as well. That background signal would drastically reduce the contrast and on/off ratios leading to errors in the output."

With background signals washing out the intended output, necessarily computational qualities for optical transistors, such as their on/off ratio, modulation strength and signal mixing contrast have all been extremely poor. Electric transistors have high standards for these qualities to prevent errors.

The search for materials that can serve in optical transistors is complicated by additional property requirements. Only "nonlinear" materials are capable of this kind of optical signal mixing.

To address this issue, Agarwal's research group started by finding a system which has no background signal to start: a nanoscale "belt" made out of cadmium sulfide. Then, by applying an electrical field across the nanobelt, Agarwal and his colleagues were able to introduce optical nonlinearities to the system that enable a signal mixing output that was otherwise zero.

"Our system turns on from zero to extremely large values, and hence has perfect contrast, as well as large modulation and on/off ratios," Agarwal said. "Therefore, for the first time, we have an optical device with output that truly resembles an electronic transistor."

With one of the key components coming into focus, the next steps toward a photonic computer will involve integrating them with optical interconnects, modulators, and detectors in order to demonstrate actual computation.

Facts, background information, dossiers
  • transistors
  • optical switches
  • electric fields
  • materials science
  • light waves
More about University of Pennsylvania
  • News

    Ultrathin and ultralight 'nanocardboard'

    When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure Now, a team of Penn Engineers h ... more

    How to control liquid crystal patterns

    When Lisa Tran set out to investigate patterns in liquid crystals, she didn't know what to expect. When she first looked through the microscope, she saw dancing iridescent spheres with fingerprint-like patterns etched into them that spiraled and flattened as the solution they were floated i ... more

    Smart materials used in ultrasound behave similar to water, Penn chemists report

    A team of researchers at the University of Pennsylvania is gaining new insight into the smart materials used in ultrasound technology. While forming the most thorough model to date of how these materials work, they have found striking similarities with the behavior of water. The research wa ... more

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE