Computing With Photons Instead Of Electrons (Or What Is Optical Computing)

By John Oncea, Editor

Optical computing is a technology that uses light waves instead of electrical signals to perform computational tasks. This approach aims to leverage the properties of light for data processing, storage, and communication in computing systems.

Optical computing, also known as photonic computing, is a computing technology that uses light waves produced by lasers for data processing, data storage, and communication. It offers higher bandwidth than conventional computers that use electrons, as well as reduces power consumption by eliminating optical-electrical-optical conversions.

Researchers creating an optical digital computer system by replacing current computer components with an optical equivalent are finding some success. However, the resulting devices consume 30% of their energy converting electronic energy into photons and back, and the conversion also slows the transmission of messages. An all-optical computer would eliminate the need for optical-electrical-optical (OEO) conversions, thus reducing electrical power consumption.

Used in devices like synthetic-aperture radar and optical correlators for object detection and data classification, optical computing requires an optical transistor, achieved using crystal optics and materials with a nonlinear refractive index. It operates by building logic gates and central processing unit components with nonlinear optical crystals to manipulate light beams.

As it stands, some doubt the viability of optical computing, questioning if it will be able to compete with semiconductor-based electronic computers in terms of speed, power consumption, cost, and size. Some critics suggest that real-world logic systems require logic-level restoration, cascadability, fan-out, and input-output isolation, all of which are currently provided by electronic transistors at low cost, low power, and high speed.

To overcome these challenges and be more than “cool” or applicable to a few niche applications, breakthroughs in nonlinear optical device technology would be required. But in our ongoing effort to improve size, weight, power, and cost (SWaP-C) researchers such as Alireza Marandi are going to continue to pursue the technology.

We’ll look at Marandi’s research later but first, what is optical computing?

Using Light Waves To Perform Computation Tasks

Optical computing is a technology that uses light waves instead of electrical signals to perform computational tasks. This approach utilizes optical elements such as lasers, fiber optics, and photonic integrated circuits to manipulate and process light signals. Many current implementations involve optical-electronic hybrid systems, integrating optical components into traditional computer architectures.

The concept of optical computing first gained traction in the 1960s with the invention of the laser, writes TechHQ. Since then, research and development in this field have progressed, with significant advancements occurring from the 1990s onwards.

While fully optical computers are not yet commercially available, photonic technology has made significant inroads over the years. According to TechTarget, these advancements include:

• Telecommunications: Fiber optic data transmission is now commonplace in digital communications.
• Data storage: Optical technology is used in CD-ROM drives and related devices.
• Printing and imaging: Laser printers, photocopiers, and scanners utilize optical technology.
• Specialized computing: Application-specific devices like synthetic-aperture radar (SAR) and optical correlators use principles of optical computing.

Despite its potential, optical computing struggles with nonlinear interactions, a function computation requires that is weaker for light than for electronic signals. In addition, developing large-scale integrated optical circuits remains a challenge, as does ensuring compatibility with existing electronic systems, a process that is crucial for adoption.

The future of optical computing is still evolving with researchers exploring areas such as high-speed integrated optoelectronic devices, low-loss waveguides, large-scale integration techniques, mitigating nonlinear effects, and developing hybrid optoelectronic systems.

Companies like Lightelligence are working on next-generation computing hardware using photonics, aiming for exponential improvements in computing power and energy efficiency. While there is controversy about whether photonic computers can fully replace electronic computers, the technology shows promise for specific applications and as a complement to traditional computing systems. The field continues to advance, and future breakthroughs may lead to more widespread adoption of optical computing technologies.

Advances In Optical Computing Research

One of those “future breakthroughs” is now just a breakthrough thanks to the aforementioned Marandi, an assistant professor of electrical engineering and applied physics at Caltech.

SciTechDaily reports Marandi used “optical hardware to realize cellular automata, a type of computer model consisting of a “world’ (a gridded area) containing ‘cells’ (each square of the grid) that can live, die, reproduce, and evolve into multicellular creatures with their own unique behaviors. These automata have been used to perform computing tasks and, according to Marandi, they are ideally suited to photonic technologies.”

“If you compare an optical fiber with a copper cable, you can transfer information much faster with an optical fiber,” Marandi says. “The big question is can we utilize that information capacity of light for computing as opposed to just communication? To address this question, we are particularly interested in thinking about unconventional computing hardware architectures that are a better fit for photonics than digital electronics.”

Cellular automata are simulated cells that follow a basic set of rules that can lead to incredibly complex behaviors. Basic cellular automata “can be used for random number generation, physics simulations, and cryptography,” SciTechDaily writes. “Others are computationally as powerful as conventional computing architectures — at least in principle.” More advanced cellular automata can be used for practical computing tasks such as identifying objects in an image and Marandi says these benefits make cellular automata well suited to optical computing.

First, they eliminate the need for many of the components that create problems for optical computing including gates, switches, and devices that are otherwise required for moving and storing light-based information. Second, cellular automata can run incredibly fast due to the high-bandwidth nature of optical computing.

“In Marandi’s optical computing device,” writes SciTechDaily, “the cellular automaton’s cells are just ultrashort pulses of light, which can allow operation up to three orders of magnitude quicker than the fastest digital computers. As those pulses of light interact with each other in a hardware grid, they can process information on the go without being slowed down by all the layers that underlie traditional computing. In essence, traditional computers run digital simulations of cellular automata, but Marandi’s device runs actual cellular automata.”

Marandi concludes, “The ultrafast nature of photonic operations, and the possibility of on-chip realization of photonic cellular automata could lead to next-generation computers that can perform important tasks much more efficiently than digital electronic computers.”