Structured Optical Toroidal Vortices with Rotational Symmetry

Toroidal vortices, as intriguing topological structures, play a fundamental role across a wide range of physical fields. In this study, we theoretically propose a family of structured optical toroidal vortices as generalized forms of toroidal vortices in paraxial continuous wave beams. These structured optical toroidal vortices exhibit unique rotational symmetry while preserving the topological properties of standard toroidal vortices. The three-dimensional topological structures demonstrate l-fold rotational symmetry, which is closely related to the topological charges. Structured toroidal vortices introduce additional topological invariants within the toroidal light field. These topological light fields hold significant potential applications in the synthesis of complex topological structure and optical information encoding

Toroidal phase topologies within paraxial laser beams

Abstract Control of topologies in structured light fields with multi-degrees of freedom integrates fundamental optical physics and topological invariance. Beyond the simple phase vortex, three-dimensional (3D) topological singularities and related nonsingular textures have recently gained significant interest. Here, we experimentally demonstrate the creation of a family of toroidal phase topologies within paraxial laser beams. By employing single two-dimensional (2D) phase control, we generate propagating 3D topological textures, effectively embodying the topological configuration of a four-dimensional (4D) parameter space. The resulting light fields exhibit amplitude isosurfaces of toroidal vortices and hopfionic phase textures, both controlled by topological charges. The ability to prepare scalar phase textures of light offers new insights into the high-dimensional control of complex structured textures and may find significant applications in light-matter interactions, optical manipulation, and optical information encoding

Plasmonic Focusing of a High-Order Cylindrical Vector Beam for On-Chip Detection

We investigate the interaction between cylindrical vector beams (CVBs) and metallic annular structures. The mechanisms for plasmonic focusing and field distributions are studied both analytically and numerically. We demonstrate that the focusing patterns are locked with the order of CVBs due to the polarization selectivity for the excitation of plasmonic fields, which can be employed as a simplified yet efficient means of characterizing and detecting CVBs. The robustness of the focusing pattern is analyzed as a deviation between the centers of the CVBs and nanoring is introduced, providing a quantitative indicator of the relationship between the maximum deviation value and the focusing patterns. Our research contributes to a deeper understanding of interactions between CVBs and nanostructures, paving the way for novel applications in light detection and optical imaging

Broadband On-Chip Directional Coupler with Oblique Nanoslits

Directional coupling of light at the nanoscale plays a significant role in both fundamental research and practical applications, which are crucial for the development of on-chip photonic devices. In this work, we propose a broadband directional coupler for surface plasmon polaritons (SPPs) utilizing a pair of obliquely perforated nanoslits. We demonstrate that tilting the slits significantly enhances the sensitivity of plasmonic coupling phase variation to the wavelength of the incident light, enabling precise wavelength-dependent control over SPP propagation. By optimizing the width and tilting angle of each nanoslit, we achieve an extinction ratio exceeding 10 dB with a bandwidth exceeding 400 nm and a maximum unidirectional transmission of up to 30 dB. This broadband directional SPP coupler presents a promising platform for the design and fabrication of integrated plasmonic circuits and high-performance optical devices and sensors

Poincaré sphere analogue for optical vortex knots

We propose a Poincaré sphere (PS) analogue for optical vortex knots. The states on the PS analogue represent the light fields containing knotted vortex lines in three-dimensional space. The state changes on the latitude and longitude lines lead to the spatial rotation and scale change of the optical vortex knots, respectively. Furthermore, we experimentally generate and observe these PS analogue states. These results provide new insights for the evolution and control of singular beams, and can be further extended to polarization topology.</jats:p

Optical vortex knots and links via holographic metasurfaces

Vortices arise in many natural phenomena as dark points of total destructive interference. Sometimes they form continuous lines and even enclosed loops with knotted or linked topologies in three spatial dimensions. Since the mathematical topology was introduced into physics, from hydrodynamics, condensed matter physics to photonics, and other modern physical fields, scientists have been exploring the related topological essences of vortex knots; hence, the topology is a forefront topic in different physical systems. Owing to the reliability and observability of light in free space, optical vortex knots and links are the most studied physical topologies. Here, we review some of these developments with a focus on optical vortex knots and links. We first introduce the brief historical perspective and structural properties of optical vortices. Then, we trace the progress on the theoretically constructing, experimentally generating, and characterizing methods of topological light fields. Wherein, we review recent developments of holographic metasurfaces and their applications in generating ultrasmall optical vortex knots. At last, we envision the possible challenges and prospects of topological light fields

Metasurface-assisted multidimensional manipulation of a light wave based on spin-decoupled complex amplitude modulation

Achieving arbitrary manipulation of the fundamental properties of a light wave with a metasurface is highly desirable and has been extensively developed in recent years. However, common approaches are typically targeted to manipulate only one dimension of light wave (amplitude, phase, or polarization), which is not quite sufficient for the acquisition of integrated multifunctional devices. Here, we propose a strategy to design single-layer dielectric metasurfaces that can achieve multidimensional modulation of a light wave. The critical point of this strategy is spin-decoupled complex amplitude modulation, which is realized by combining propagation and geometric phases with polarization-dependent interference. As proofs of concept, perfect vector vortex beams and polarization-switchable stereoscopic holographic scenes are experimentally demonstrated to exhibit the capability of multidimensional light wave manipulation, which unlocks a flexible approach for the multidimensional manipulation of a light wave such as complex light-wave control and vectorial holography in integrated optics and polarization-oriented applications.</jats:p

Observation of optical vortex knots and links associated with topological charge

Knots and links, as three-dimensional topologies, have played a fundamental role in many physical fields. Despite knotted vortex loops having been shown to exist in the light field, the three-dimensional configuration of vortex loop is fixed due to their topological robustness, making the fields with different topologies independent of each other. In this work, we established the mapping between the torus knots/links and the integer topological charge of the optical vortex, and demonstrated the change of the intermediate state with fractional charges. Furthermore, we experimentally observed the transformation process of the three-dimensional topological structure by only changing the topological charge. Remarkably, we revealed two different reconnection mechanisms associated with the odd or even index of the torus topology. We hope these results may provide new insight for the study of singular optics and evolution in other physical fields.</jats:p