Water whirlpools, smoke rings, violent tornados and spiral galaxies are all examples of twists in fluids, although very different each other. Analogous twists, but in the realm of light, have been created by the research group coor­dinated by Antonio Ambrosio at the IIT-Istituto Italiano di Tecno­logia (Italian Institute of Techno­logy) in Milano. The results show the realization of 100 light vortices, coupled to form an ordered structure, a light crystal. 

Mutual interaction of light and nano­structured materials is the focus of the research of Antonio Ambrosio of the research line Vectorial Nano-imaging at IIT in Milano. Twisted light generators have been developed in the last few years, but they typically create a single vortex propa­gating alone in free space. The researchers have shown instead that it is possible to create 100 light vortices, coupled into an ordered light crystal. Their results show how a nanostructure surface can be employed as a mask to simul­taneously control all the parameters of several laser beams, not just their intensity. The group showed that this is possible by designing an array of metasurfaces, i.e. nano­structured optical devices. The realized meta­surfaces shape the wavefront of light like a corkscrew, generating an optical vortex.

Inserting the meta­surface array inside a laser cavity, where light conti­nuously bounces between two mirrors, open the door to new properties, such as the self-healing of a defect in the system or the recon­figurability of the number of twists that light makes. Such properties result from the inter­action between different vortices of the crystal: each vortex is in fact modelled by the inter­action with other vortices of a tunable network.

The ability to adjust the number of twists on demand is a unique feature of the meta­surface laser. Although the devices have a fixed design and can only generate one specific type of optical vortex in free space, when inserted in a laser cavity, the topology can be changed by simply tuning a cavity mirror. This func­tionality could be used to dynamically modulate light imparting useful information in the twists for optical communi­cations.

The system is robust and it also has the potential to process information encoded in different coupled systems, including far and enormous galaxies. Thanks to these new results, it is now possible to simulate in the lab complex coupled systems, with order altered by stable defects, difficult to be repro­duced otherwise since involving ginormous scale, like galaxies, or part of extreme hydro­dynamic systems. In the next steps, the researchers will inves­tigate how to tune the strength of the interaction among the vortices and extend the system to an even larger number of vortices. (Source: IIT)

Reference: M. Piccardo et al.: Vortex laser arrays with topological charge control and self-healing of defects, Nat. Phot., online 11 April 2022; DOI: 10.1038/s41566-022-00986-0

Link: Center for Nano Science and Technology, Fondazione Istituto Italiano di Tecnologia IIT, Milan, Italy