Light-based computer could outpace traditional electrical chip designs

A new type of computer that uses light rather than electricity could perform calculations faster, using less energy and less space.

Computer chips are made up of millions or billions of logic gates. These tiny components carry out the most basic of operations, such as checking if one bit of data matches another. It is by combining these gates in vast numbers that tasks like downloading a file, playing a video or running a computer game are managed.

Traditional chips work by ferrying electrons, but Yi Zhang at Aalto University, Finland, and his colleagues have managed to create optical logic gates that perform the same functions with light.

Optical computers have been created before, but they involve complex hardware and are limited to certain applications. Zhang says these new gates can be built from a single layer of molybdenum disulphide crystals just 0.65 nanometres thick using existing manufacturing techniques and they could be designed to carry out universal tasks in a small package.

Because photons move faster than electrons do in a circuit, this could speed up calculations, and because they also move without resistance, they could do the same job using less energy.

The team’s approach uses circularly polarised light. This involves a light wave that appears to spin around its axis of travel, turning either clockwise or anticlockwise. A traditional bit in a computer is made up of a positive or negative electrical charge – represented by 0 or 1 – but in this new optical computer, bits are represented by either clockwise-polarised light or anticlockwise-polarised light.

In the optical computer, the logic gates are made from crystalline materials that are sensitive to the direction of spin of these polarised light beams. Using optical filters and other components, these gates can be built up to recreate traditional gates.

The team demonstrated working optical gates that recreate the traditional gates known as XNOR, NOR, AND, XOR, OR and NAND, which all carry out different operations on data. The researchers also showed that these operations can be carried out on data in parallel rather than in series, which could potentially pave the way for big improvements in the efficiency and speed of calculations.

“We hope that all-optical computers can be made in the future,” says Zhang. “The biggest advantage is the super fast speed of optical chips over traditional chips. In addition, light has the ability of parallel processing and has less energy consumption, while electronic devices consume more energy due to resistance.”

Zhang says future work will investigate how optical logic gates could be used to create either hybrid classical and quantum computers or to create optical quantum logic gates. This is because one common branch of quantum computing research already uses photons to transmit data.