Light-Based Optical Computing for Ultrafast Electronics

Andrew Corselli

A home computer operating 1 million times faster than the most expensive hardware on the market seems far-fetched. That level of computing power seen as the industry standard seems even more outrageous, right? Well, not if researchers from the University of Arizona have anything to say about it.

The team hopes to pave the way for such a reality using light-based optical computing — a marked improvement from the semiconductor-based transistors that currently run the world.

“Semiconductor-based transistors are in all of the electronics that we use today,” said team lead and U of A’s Mohammed Hassan, Assistant Professor of Physics and Optical Science. “They’re part of every industry — from kids’ toys to rockets — and are the main building blocks of electronics.”

Semiconductors in electronics rely on electrical signals transmitted via microwaves to switch — either allow or prevent — the flow of electricity and data, represented as either on or off. Hassan said the future of electronics will be based instead on using laser light to control electrical signals, opening the door for the establishment of optical transistors and the development of ultrafast optical electronics.

Hassan and his team discuss using all-optical switching of a light signal on and off to reach data transfer speeds exceeding a petahertz, measured at the attosecond time scale. An attosecond is one quintillionth of a second, meaning the transfer of data 1 million times faster than the fastest semiconductor transistors.

The team was able to register the on and off signals from a light source happening at the scale of billionths of a second. This was accomplished by taking advantage of a characteristic of fused silica, a glass often used in optics. Fused silica can instantaneously change its reflectivity, and by using ultrafast lasers, the team was able to register changes in a light signal at the attosecond time scale. The work also demonstrated the possibility of sending data in the form of one and zero, representing on and off via light at previously impossible speeds.

“This new advancement would also allow the encoding of data on ultrafast laser pulses, which would increase the data transfer speed and could be used in long-distance communications from Earth into deep space,” Hassan said. “This promises to increase the limiting speed of data processing and information encoding and open a new realm of information technology.”

Here is a Tech Briefs interview, edited for length and clarity, with Hassan.

Tech Briefs: What were some of the biggest technical challenges you faced?

Hassan: The main idea of the attosecond optical switching was simple but sophisticated. The main challenge was the capability to measure the switching signal because we did not know the contrast of the switching signal at that time. After a few iterations and optimization, we were able to measure the switching signal with 20 percent contrast, which, to our knowledge, had not have been reported before.

Tech Briefs: Can you explain in simple terms how the process works?

Hassan: The synthesized ultrafast laser pulse is generated using our unique Attosecond Light Field Synthesizer. This pulse is focused, interacts with the fused silica (glass), and changes its property. Then, the glass is converted from a fully transparent material to a partially reflected material in the presence of the laser pulse. Hence, this reflected signal is controlled and switched on and off by controlling the waveform shape of the laser pulse, which can be synthesized with attosecond resolution by the Attosecond Light Field Synthesizer.

Tech Briefs: Do you have any set plans for further research/testing? What are your next steps? Next goal(s)?

Hassan: In this research direction, we are currently working on controlling and switching the current signal in the commercial transistors, which is the next step forward to develop and engineer attosecond optical transistors and ultrafast photonics. I also have another direction of research where I am developing the electron camera, which would allow imaging the quantum electron motion in real time and space.

Tech Briefs: You said that the future of electronics will be based instead on using laser light to control electrical signals, opening the door for the establishment of “optical transistors” and the development of ultrafast optical electronics. How far away from that are we?

Hassan: Due to technical challenges, semiconductor and processing developments have deviated from Moore’s law in recent decades. For example, the transistors’ speed has been limited to 900 MHz over the last 10 years. Although, we need faster communications and computing power to catch up with other technological advances. Hence, I strongly believe a new, alternative electronics, such as ultrafast light-based electronics (optoelectronics), is required.

In the last two decades, fueled by the recent profound laser development, the capability of controlling the shape of the ultrafast laser waveform with sub-femtosecond resolution allowed us to demonstrate all-optical switching with attosecond resolution paving the way to establish Petahertz optical transition, which is 1 million times faster than the current semiconductor.

Moreover, we utilized this capability to encode data on ultrafast laser pulses. This advancement promises to increase the limiting speed of data processing and information encoding to rates beyond petabit/s. Therefore, I strongly believe that ultrafast photonics is the future of the electronics industry.

Tech Briefs: Do you have any advice for engineers aiming to bring their ideas to fruition?

Hassan: In the last decades, we have seen significant technological developments. Now we carry in our pocket computers more powerful than the computers used to send a man to the moon. This technology is based on scientific breakthroughs that happened in the last century. The gap in time between the science achievement and the technology developed was due to the limited networking and communications at that time.

Now I think we are in a much better situation, and the technology developed by engineers can benefit momentarily from the scientific research done by the scientists. So, I would recommend that the engineer reach out to scientists and build strong collaboration to transferring the scientific achievements to real-life applications.

Tech Briefs: Anything else you’d like to add?

Hassan: I anticipate that the ultrafast optical switching and data encoding in this work will open the door for a new era of information technology if the technology industrial sectors invest in it.

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