Photograph: Personal archive
Publish Date: 18.06.2021
Category: Researchers in focus , ERC & MSCA
Fiber optic data transmission exploiting the photon as the information carrier rather than the electron has revolutionized our ability to process ever-increasing amounts of data in record time. Being an integral part of consumer high-speed internet, it is one of the most well-known achievements of the field of photonics—the study of the generation, transmission, manipulation and detection of light. However, current technologies based on costly and power-hungry photon→electron→photon conversion appear insufficient in light of environmental constraints.
Going beyond state-of-the-art solid materials for photonics applications, the OPTOSOL project is investigating novel light-matter interactions in so-called “topological soft materials”—fluid-like materials which embed robust structures allowing the manipulation of the flow of light at the microscopic scale. The objective of the project was to determine the guiding principles of light in chiral soft materials which cannot be superimposed on their mirror images—like the left and right hands. These malleable materials can be reconfigured in real-time with external fields and allow the exploration of alternative routes for the management of light for which solid-state materials are not best suited.
The OPTOSOL project was funded by the EU as a Marie Skłodowska Curie Individual Fellowship and implemented by Dr. Guilhem Poy at the Faculty of Mathematics and Physics (University of Ljubljana) under the supervision of Prof. Slobodan Žumer. The theoretical and numerical work carried out in Ljubljana was complemented by collaborative experiments in the group of Prof. Ivan Smalyukh from the University of Colorado (Boulder, USA).
The optical materials investigated were the liquid crystals (LCs) commonly used in the displays of our mobile phones, computers and TVs, with the additional twist of chirality. Chirality is a fundamental property of matter which requires that an entity (going from molecules to tangible macroscopic objects) is distinguishable to its mirror image, like a left or right hand. Such a property has fundamental consequences on the physical behaviour of materials: for example, think about how maple tree seeds fall with a rotational motion due to their helix-like shape (a very common example of chiral shape).
Building up on fundamental works by the groups of Assanto and Karpierz [1,2], one of our achievements was to show that chirality can also play a major role in the optical response of materials [3]. More specifically, we focused on so-called optical solitons—self-focused laser beams which can propagate in a straight fashion without dispersing energy—and showed that the critical beam power necessary to generate them can be sharply decreased by adding chiral molecules into the LC propagating media. Since these optical solitons can be considered as an ‘optical wire’ bringing photons from a point A to a point B without loss, similar to the electric wires of electronic devices, the chirality enhancement effect that we theoretically and experimentally demonstrated could find its use in the design of optical and photonics devices with low power consumption.
But the story does not end here! Indeed, introducing chiral molecules into LCs also allows the stabilization of very robust structures called topological solitons. Like balls of yarn which cannot be easily unrolled at once, topological solitons are ‘knotty’ objects which cannot be destroyed in a continuous manner. Our second achievement was to show that these intriguing and robust objects can be used to manipulate and guide the flow of photons in chiral LCs [4], similar to a billiard ball deflecting the trajectory of another moving ball after collision (see image below). Combining our two achievements opens a new paradigm of interconnected optically-active devices based on topological solitons: by using multiple ball-like solitons such as the one in the image below, one could create the optical analogous of electronic logic gates, i.e. devices which can make computations based on light instead of electrons.
Simulated interaction of light (in green) with a topological soliton (bright circular object), with deflection (top) or lensing (bottom) behaviour depending on the beam incidence position. White lines correspond to the theoretically predicted direction of propagation of photons. The white bar represents 100 μm.
References
[1] Karpierz, M.A., ‘Solitary waves in liquid crystalline waveguides’, Physical Review E 66, 036603 (2002).
[2] Peccianti, M., Dyadyusha, A., Kaczmarek, M., and Assanto, G., ‘Tunable refraction and reflection of self-confined light beams’, Nature Physics 2, 737 (2006).
[3] Poy, G., Hess, A.J., Smalyukh, I.I., Žumer, S., ‘Chirality-Enhanced Periodic Self-Focusing of Light in Soft Birefringent Media’, Physical Review Letters 125, 077801 (2020).
[4] Hess, A.J., Poy, G., Tai, J.-S. B., Žumer, S. and Smalyukh, I. I., ‘Control of Light by Topological Solitons in Soft Chiral Birefringent Media’, Physical Review X 10, 031042 (2020).