Reaching the Speed Limit of Technology: Ultrafast Optical Transistors

Friday - July 28 2023, 14:25 UTC - 1 year ago

Scientists and engineers are researching faster transistors based on a category of materials called semiconductors that have special electrical properties. Researchers are using laser-based systems equipped with optical transistors, which use photons to control reflected light to transfer data more quickly than current systems.

If you’ve ever wished you had a faster phone, computer, or internet connection, you’ve encountered the personal experience of hitting a limit of technology. But there might be help on the way. Over the past several decades, scientists and engineers like me have worked to develop faster transistors, the electronic components underlying modern electronic and digital communications technologies. These efforts have been based on a category of materials called semiconductors that have special electrical properties .

Silicon is perhaps the best known example of this type of material. But about a decade ago, scientific efforts hit the speed limit of semiconductor-based transistors. Researchers simply can’t make electrons move faster through these materials. One way engineers are trying to address the speed limits inherent in moving a current through silicon is to design shorter physical circuits—essentially giving electrons less distance to travel .

Increasing the computing power of a chip comes down to increasing the number of transistors. However, even if researchers are able to get transistors to be very small, they won’t be fast enough for the faster processing and data transfer speeds people and businesses will need. My research group’s work aims to develop faster ways to move data, using ultrafast laser pulses in free space and optical fiber .

The laser light travels through optical fiber with almost no loss and with a very low level of noise. In our most recent study, published in February 2023 in Science Advances, we took a step toward that, demonstrating that it’s possible to use laser-based systems equipped with optical transistors, which depend on photons rather than voltage to move electrons, and to transfer information much more quickly than current systems—and do so more effectively than previously reported optical switches .

At their most fundamental level, digital transmissions involve a signal switching on and off to represent ones and zeros. Electronic transistors use voltage to send this signal: When the voltage induces the electrons to flow through the system, they signal a 1; when there are no electrons flowing, that signals a 0. This requires a source to emit the electrons and a receiver to detect them. Our system of ultrafast optical data transmission is based on light rather than voltage .

Our research group is one of many working with optical communication at the transistor level—the building blocks of modern processors—to get around the current limitations with silicon. Our system control reflected light to transmit information. When light shines on a piece of glass, most of it passes through, though a little bit might reflect. That is what you experience as glare when driving toward sunlight or looking through a window .

We use two laser beams transmitted from two sources passing through the same piece of glass. One beam is constant, but its transmission through the glass is controlled by the second beam. By using the second beam to shift the properties of the glass from transparent to reflective, we can start and stop the transmission of the constant beam, switching it on and off like a transistor.