Photonics breakthrough: structured light on a silicon chip

In everyday life light is experienced through optical rays or beams. However, beams of light can also be shaped to take the form of spirals; so-called vortex beams, endowed with unusual properties. Such beams can make dust particles spin, just like they move along some intangible spirals. Light modes with such added structure are called ‘structured’ and more exotic forms of structured light can be attained in artificial optical materials — metamaterials, where multiple light waves come together and combine to create complex forms of light.

In two recent studies, published in Science Advances and Nature Nanotechnology, City College of New York researchers have created structured light on a silicon chip and used this added structure to attain new functionalities and control. To this aim, two-dimensional optical metamaterials, referred to as metasurfaces, and hosting a special kind of structured light spinning around like vortex beams, were created. By experiments carried out in Alexander Khanikaev’s laboratory at City College, researchers demonstrated a new kind of trap to confine structured optical modes and to guide them on the chip.

In their Science Advances study, the researchers showed that, by slowly changing the pattern of metasurface in two directions, one can create optical resonators which trap structured light and radiate it. This underlying structure gave rise to unusual patterns of the radiated light — optical vortex beams. Applying similar slow change in the pattern in one direction, as reported in Nature Nanotechnology, researchers have created waveguides for structured light. These channels allow guiding optical signals while preserving the internal structure of light. As such, this is similar to the flow of currents in wires.

Such currents have been of great interest in electronics recently and a new class of electronic devices, referred to as spintronic or valleytronic, was envisioned. In such devices it is not the flow of charge by itself that would transfer signals, but spin or valley of electrons, which promises a range of advantages in parison to conventional electronic devices.

Khanikaev’s research envisions a similar concept, but with light rather than electrons. However, in contrast to electronic systems, optics and photonics have a significant advantage — optical modes do not suffer from decoherence to the same degree as electrons, which can be vital for quantum technologies. The demonstrations by Khanikaev’s team can be useful for quantum applications for many reasons. Therefore, the added structure of optical modes can be used to encode quantum information in the form of quantum bits. This information can then be transported on a chip or emitted into free space for communicating quantum information between remote systems.

Khanikaev’s team is currently working on implementing these ideas with quantum states of structured light and realising quantum logic in its photonic nanostructures.

Image credit: Dr Svetlana Kiriushechkina