Scientists Unlock Light-Based Computer Chips That Need Tiny Power

Researchers in China have successfully made a beam of light maintain three stable states inside a silicon device just 20 micrometers wide, according to a study published in Nature Nanotechnology.

For comparison, the structure is thinner than a human hair.

This breakthrough can help achieve more practical photonic computing. Photonic computing uses light instead of electricity to power its chips, so it only needs tiny amounts of power.

Could Help Build More Advanced Light-Based Computers

The research shows that careful physical design can strengthen and control the normally weak non-linear behavior of light, even on an extremely small silicon chip.

This could provide a useful building block for future optical neural networks, which use light to perform calculations inspired by artificial neural networks.

It could also help develop neuromorphic processors, which are computing systems designed to process information more like the human brain.

By allowing individual optical units to hold more than two states, such systems could potentially handle more complex information using light.

Tiny Device Uses Very Little Power

Researchers from Peking University in Beijing and Harbin Engineering University in northeast China achieved the three-state system using only 240 microwatts of switching power.

That is less power than a typical laser pointer uses.

The researchers also built a prototype multi-valued optical memory device using the same technology. Instead of storing information only as two possible values, such a device could use several stable states.

Light Goes Beyond Simple On and Off

Conventional digital systems usually work with two states: on and off, represented as 1 and 0.

The researchers were able to make light remain stable in three different states instead. This is known as tristability.

Tristability is a form of multistability, which simply means that a system can stay in several stable states under the same conditions and switch between them when given the right input.

For computing, this matters because a single unit could potentially represent more information than a traditional two-state system.

The technology could therefore be useful for both photonic computing and optical data storage.

Why This is Difficult

Making light behave this way on extremely small chips is difficult because light normally produces very weak non-linear effects at the micro- and nano-scale.

A non-linear effect means the response of the system does not simply increase in a predictable straight line when more light is added. These effects are important because they allow light to switch between different stable states.

On tiny chips, however, those effects are usually too weak to easily produce reliable multistability.

Special Light-Coupling Method

To overcome the problem, the team used a mechanism called near-exceptional-point coupling.

In simple terms, the researchers created two light resonance modes inside a tiny photonic crystal cavity.

A resonance mode is a particular way light can repeatedly bounce or oscillate inside a structure.

The researchers then pushed the two modes close to an unusual condition called an exceptional point. Near this point, the two modes interact very strongly, with their wavelengths moving closer together and their linewidths becoming similar.

This allows the tiny cavity to trap light efficiently while still exchanging energy with the outside world.

That combination helps create the conditions needed for light to maintain several stable states.

Light Can Stay Trapped for Longer

The microcavity reached a quality factor of up to one million.

The quality factor, or Q factor, describes how well a cavity can hold light before its energy fades away. A higher number means the light can keep oscillating inside the cavity for longer.