Researchers at Caltech used optical hardware to realize cellular automata, a type of computer model consisting of a “world,” or grid containing “cells” — represented by each individual square of the grid — that can live, die, reproduce, and evolve into multicellular creatures with unique behaviors. These automata, which have been used to perform computing tasks, are ideally suited to photonic technologies, according to Caltech assistant professor of electrical engineering and applied physics Alireza Marandi. “If you compare an optical fiber with a copper cable, you can transfer information much faster with an optical fiber,” Marandi said. “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.” Technically speaking, cellular automata are computational models and can be thought of as simulated cells that follow a very basic set of rules, with each type of automata operating under its own set of rules. However, beyond these simple rules, complex behaviors can emerge in the automata. One of the best-known cellular automata, called The Game of Life or Conway’s Game of Life, was developed by English mathematician John Conway in 1970. It has just four rules that are applied to a grid of “cells” that can either be alive or dead: Any live cell with fewer than two live neighbors dies, as if by underpopulation. Any live cell with more than three live neighbors dies, as if by overcrowding. Any live cell with two or three live neighbors lives to the next generation. Any dead cell with exactly three live neighbors will come to life, as if by reproduction. A computer running The Game of Life repeatedly applies these rules to the world in which the cells live at a regular interval, with each interval being considered a generation. Within a few generations, those simple rules lead to the cells organizing themselves into complex forms with evocative names such as loaf, beehive, toad, and heavyweight spaceship. Researchers at Caltech have developed a method of photonic computing based on cellular automata. Courtesy of Caltech. Basic, or elementary, cellular automata like The Game of Life appeal to researchers working in mathematics and computer science theory, although they can have practical applications, too. Some of the elementary cellular automata can be used for random number generation, physics simulations, and cryptography, for example. Others are computationally as powerful as conventional computing architectures — at least in principle. More advanced cellular automata, which have more complicated rules, can be used for practical computing tasks such as identifying objects in an image. “While we are fascinated by the type of complex behaviors that we can simulate with a relatively simple photonic hardware, we are really excited about the potential of more advanced photonic cellular automata for practical computing applications,” Marandi said. Since information processing is happening at an extremely local level — in cellular automata, cells interact only with their immediate neighbors — they eliminate the need for much of the hardware that makes photonic computing difficult. This hardware includes the various gates, switches, and devices that are otherwise required for moving and storing light-based information. And the high-bandwidth nature of photonic computing means cellular automata can run incredibly fast. In traditional computing, cellular automata might be designed in a computer language, which is built upon another layer of “machine” language below that, which itself sits atop the binary zeroes and ones that make up digital information. In contrast, in Marandi’s photonic computing device, the cellular automaton’s cells are just ultrashort pulses of light that 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. “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,” Marandi said. The research was published in Light: Science & Applications (www.doi.org/10.1038/s41377-023-01180-9).
