Researchers Seek Out “Fastest Ever Logic Gates” Via Lasers

May 16, 2022 by Jake Hertz

Reaching for faster compute speeds and bringing lightwave electronics mainstream, researchers from the University of Rochester have created lightwave-based logic gates.

On the lowest level, the speed of electronics is fundamentally limited by the laws of nature. As opposed to conventional electrical currents, many in the industry have explored faster methods, including fiber optics for communications and photonics for integrated circuits.


A high-level representation of synchronized laser pulses (red and blue), which creates a burst of charge carriers to produce a net current. Image used courtesy of the University of Rochester and Michael Osadciw


With this idea in mind, researchers at the University of Rochester are making strides in another direction: lightwave photonics. Recently, the research group from Rochester made headlines when they announced the first-ever demonstration of operating logic gates based on lightwave photonics.

In this article, we’ll discuss the concept of lightwave photonics, the new research, and the potential implications of the work.


Brief Overview of Lightwave Electronics

As mentioned, one technology that has found a lot of interest recently is the concept of lightwave electronics.

Lightwave electronics is a technique in which it is possible to use laser pulses to guide and speed up electronics. The concept is that an ultrashort laser pulse's extremely high-speed oscillating electric field can excite electrons in an incident material and create an effective current. 

A standard setup might include graphene-based wires which connect two gold metal electrodes, known as a gold-graphene-gold junction. When femtosecond-long laser pulses illuminate the graphene, the electrons within the graphene material are excited and sent in a particular direction. This method effectively creates a net current within the material that designers can harness for conventional electronic operation.

The benefit of lightwave electronics is that this method can produce electricity faster than many traditional methods and does not require an applied voltage. For example, generating electricity on the femtosecond time scale is roughly one million times faster than today's fastest computers.


Rochester Researchers Tackle Lightwave Logic Gates

Despite the high potential for lightwave electronics, researchers have still found it very difficult to harness to this point. However, researchers from the University of Rochester made significant advances in the field, which may open up the door to actual computation using lightwave electronics.

In their article published in Nature, the researchers describe a fundamental realization about lightwave electronics that led to further advances. 


Rochester researchers developed a logic gate from lightwave electronics.

Rochester researchers developed a logic gate from lightwave electronics. Image used courtesy of Boolakee et al


The realization is that there are two types of charge-carrying particles in the conventional gold-graphene-gold junctions, dubbed "real" and "virtual." 

In this setup, the "real" charge carriers only contribute to the residual current if the light field imprints momentum on them, which is present even after the light is no longer. "Virtual" carriers, on the other hand, disappear when the light is no longer present but still contribute to the net current by generating a net polarization.


The role of real and virtual carriers in a gold-graphene-gold junction.

The role of real and virtual carriers in a gold-graphene-gold junction. Image used courtesy of Boolakee et al

Based on this realization, the researchers found that, by changing the phase of the laser pulse, they can simultaneously influence the behavior of these two forms of carriers. Explicitly, depending on the laser phases used, these contributions of the two carrier types can either add up or cancel out. Notably, the net current is either interpreted as a one or a zero.

All in all, the researchers effectively created the first lightwave electronics logic gate, where two inputs (i.e., the phase of two synchronized laser pulses) generate a single output (i.e., a 0 or a 1).


Future Implications of Lightwave Electronics

While the technology is still very much in its infancy, this research from Rochester could have huge implications in the field. Excitingly, the results show that it is possible to perform logic using lightwave electronics, which opens up the door to computation that can be one million times faster and more efficient than our current systems.