Like electricity in commonplace gadgets, light is used in optical devices to activate and regulate the activities of optical circuits, which are groups of components carrying optical signals. The research team discovered that heat- and light-sensitive bistable systems can be controlled by adjusting the angle of laser emission. 

Bistable systems exhibit two different states – on and off – under the same conditions. Furthermore, they can be switched reversibly between the states much like lightbulbs. They operate on the principle of memory, meaning that they retain “prehistory,” or external data, and then reproduce it to create logic elements in optical systems. 

The switch, however, is difficult to manage and needs optical systems to possess particular nonlinear properties. The researchers, in turn, were able to develop an on-off mode for optical systems using the effects of thermal heating when systems were exposed to radiation. 

The bistability and switching mode are achieved due to the properties of metastructures – ultrathin nanostructured films a few hundred nanometers thick. When a laser beam lands on a metastructure, it activates its optical resonances, which causes light particles to interact with the medium and move within the system. The energy accumulated within heats the metastructure, altering its refractive index. As a result, the system’s mode changes to on, whereas an off mode is achieved when the radiation power diminishes sufficiently as the plate cools.

Similar optical switches have existed before. Recently, a team of researchers from ITMO University and their colleagues from the National Taiwan University and the National Yang Ming Chiao Tung University have presented a record-breaking small optical structure with similar properties, which, if assisted by the new method, can be integrated into any optical or optoelectronic system as a component of the so-called hyperfine structure. 

“We sought to create a switchable system that could function as a logic element in optical computing systems. The functioning of optical computers is similar to that of electronic ones; light pulses encode data. First, we encode the information in a ray that strikes the metasurface. The metastructure then conducts logical operations that can be read from the reflected ray. This allows us to design optical circuits that can make certain optical computations and integrate them into devices,” notes Mihail Petrov, a senior researcher at ITMO’s Faculty of Physics. 

Mihail Petrov. Photo by Dmitry Grigoryev / ITMO.NEWS

Mihail Petrov. Photo by Dmitry Grigoryev / ITMO.NEWS

Optical switches may also be used for optical power filters, which, akin to electronic filters, limit the current in an electrical grid. The same happens inside an optical system: optical power limiters prevent the power that is supplied to the device from exceeding a certain value in order to avoid damage.

“Our next step is to understand how we may best exploit advances in neuromorphic computers, which are optical computers that function similarly to a brain using neural system principles. Currently, neural networks are tailored for conventional computers, and their architecture isn’t fully appropriate for fulfilling AI potential. Hence, if we want to boost the efficacy of neural networks, we need to run them on devices that use a similar method,” says Alexander Chernov, the head of the Magnetic Heterostructures and Spintronics Lab at MIPT.

The research is conducted within the scientific collaboration initiative Klever supported by the Priority 2030 national program.