Vortices exhibit unique topological features and have been observed in various physical systems, including condensed matter. The study of vortices has led to the discovery of new phases of matter. Optical vortices (OVs) are a related phenomenon in electromagnetic fields, featuring a zero-intensity singular point and a spiral phase front. They have been extensively studied and applied in diverse fields, such as information processing and super-resolution microscopy.

However, conventional OVs rely on fixed structural singularities, limiting their dynamic, interactive, and quasi-particle-like properties. Recent research has reported structural singularity-free generation of OVs, but with limitations in external control. Developing a platform for dynamic, real-space OV generation and manipulation could enable their interactive and quasi-particle-like behavior, leading to advances in photonics, including topological interactions and phase transitions. In this study, we demonstrate the spontaneous generation and active control of real-space optical vortices using a gradient-thickness optical cavity (GTOC) and an external magnetic field.

The GTOC comprises a magneto-optic nickel (Ni) layer between two silicon dioxide (SiO₂) layers on an aluminum (Al) mirror (Fig. 1a). The top and bottom SiO₂ layers’ thicknesses (h1 and h2) change gradually in nearly orthogonal directions across the GTOC. The optical thickness of the Ni layer, controllable by an external magnetic field, defines the topological texture of the reflected light from the GTOC. For specific Ni layer thicknesses, the GTOC displays a non-trivial topological phase with two singular points of zero reflection, supporting an optical vortex (w = +1) and antivortex (w = −1) (Fig. 1b). The GTOC’s structural freedom enables active generation, annihilation, and transportation of optical vortices and antivortices using an external stimulus, such as the applied magnetic field, allowing them to behave like quasiparticles (the case of the optical vortex in Fig 1c).

Utilizing ferromagnetism, electro- and thermo-optic effects, or electric gating, not only a lower external magnetic field but also alternative stimuli can activate the GTOC platform’s dynamic characteristics. Consequently, we anticipate that further development of our methodology could offer optical vortices with richer opportunities, encompassing higher-order topological textures, spatio-temporal electromagnetic singularities, and optical polarization and vortex knots.

Figure 1 (a) Schematic of the spontaneous generation of quasi-particle-like optical vortex and antivortex textures in the gradient-thickness optical cavity. (b) Theoretical schematic of the vortex (w=+1) and antivortex (w=-1) texture in the reflected light. (c) Experimental demonstration of optical vortex exhibiting quasi-particle-like nature and dynamics interacting with external magnetic fields

#Optical #vortex #Quasi-particle-like #nature

Web address for full article : https://www.nature.com/articles/s41586-022-05229-4

the Name of Journal : Nature

Laboratory web-address of the author : http://swol.kaist.ac.kr