Astigmatic hybrid SU(2) vector vortex beams: towards versatile structures in longitudinally variant polarized optics

Partially coherent twisted vector vortex beam enabling manipulation of high-dimensional classical entanglement

In this paper, we present a novel form of a partially coherent beam characterized by classical entanglement in higher dimensions. We coin the term "twisted vector vortex (TVV) beam" to describe this phenomenon. Similar to multi-partite quantum entangled states in higher dimensions, the partially coherent twisted vector vortex beam possesses distinct properties such as non-uniform polarization, vortex phase, and twist phase. Through experiments, we offer empirical evidence for these three degrees-of-freedom in the light field. The results demonstrate that the state of the light is inseparable in terms of polarization and orbital angular momentum (OAM) modes. Additionally, the twist phase introduces an additional dimension in controlling the vector vortex beam. This research reveals the possibility of new controlling dimensions in classical entanglement through the chirality of coherence within partially coherent light. Consequently, this opens up new avenues for the utilization of partially coherent light in both classical and quantum domains.

Longitudinal evolution from scalar to vector beams assembled from all-dielectric metasurfaces

Vector vortex beams (VVBs) with non-uniform polarization states have a wide range of applications, from particle capture to quantum information. Here, we theoretically demonstrate a generic design for all-dielectric metasurfaces operating in the terahertz (THz) band, characterized as a longitudinal evolution from scalar vortices carrying homogeneous polarization states to inhomogeneous vector vortices with polarization singularities. The order of the converted VVBs can be arbitrarily tailored by manipulating the topological charge embedded in two orthogonal circular polarization channels. The introduction of the extended focal length and the initial phase difference effectively guarantees the smoothness of the longitudinal switchable behavior. A generic design approach based on vector-generated metasurfaces can assist in the exploration of new singular properties of THz optical fields.

Super bursts of the orbital angular momentum in astigmatic-invariant structured LG beams

A structured Laguerre-Gaussian (sLG) beam in an optical system with an astigmatic element acquires additional degrees of freedom in the form of changing the fine structure of the beam, its orbital angular momentum (OAM), and topological charge. We have theoretically and experimentally revealed that at a certain ratio between the beam waist radius and the focal length of the cylindrical lens, the beam turns into an astigmatic-invariant one, and such a transition does not depend on the beam radial and azimuthal numbers. Moreover, in the vicinity of the OAM zero, its sharp bursts occur, the magnitude of which significantly exceeds the initial beam OAM and grows rapidly as the radial number increases.

Fast oscillations of orbital angular momentum and Shannon entropy caused by radial numbers of structured vortex beams

We address theoretical and experimental considerations of two-parameter excitation of each Hermite-Gaussian (HG) mode in composition of a structured Laguerre-Gaussian (sLG) beam. The complex amplitude of the sLG beam is shaped in such a way that the radial and azimuthal numbers of eigenmodes are entangled with each other. As a result, variations in the amplitude and phase parameters of mode excitation, although dramatically changing the intensity and phase patterns, do not change the structural stability of the beam. We reveal that the radial number of the sLG beam can cause fast oscillations of the orbital angular momentum and Shannon entropy, dramatically increasing the uncertainty of detecting the beam in some particular state. We found that despite the fast oscillations, the sLG beam has an invariant in the form of a module of the total topological charge (TC), with the exception of narrow intervals of the phase parameter, where the measurement error does not allow us to accurately measure the sign of the TC. The difference between the interpretation of informational entropy as a measure of uncertainty and a measure of information capacity is considered on the example of the measurement of Shannon entropy in the bases of LG and HG modes.

Advances on Solid-State Vortex Laser

Vortex beams (VBs) are structured beams with helical wavefronts carrying orbital angular momentum (OAM) and they have been widely used in lots of domains, such as optical data-transmission, optical tweezer, quantum entanglement, and super-resolution imaging. The ability to generate vortex beams with favorable performance is of great significance for these advanced applications. Compared with extra-cavity schemes, such as spatial light modulation, mode conversion, and others which transform other modes into vortex modes, solid-state vortex lasers can output vortex beams directly and show advantages including a compact structure, high robustness, easy to integrate, and low cost. In this review, we summarize intra-cavity generation approaches to vortex beams in solid-state lasers. Our work on 1.6μm eye-safe vector vortex lasers is also introduced.

Tunable Optical Vortex from a Nanogroove-Structured Optofluidic Microlaser

Optical vortices with tunable properties in multiple dimensions are highly desirable in modern photonics, particularly for broadly tunable wavelengths and topological charges at the micrometer scale. Compared to solid-state approaches, here we demonstrate tunable optical vortices through the fusion of optofluidics and vortex beams in which the handedness, topological charges, and lasing wavelengths could be fully adjusted and dynamically controlled. Nanogroove structures inscribed in Fabry-Pérot optofluidic microcavities were proposed to generate optical vortices by converting Hermite-Gaussian laser modes. Topological charges could be controlled by tuning the lengths of the nanogroove structures. Vortex laser beams spanning a wide spectral band (430-630 nm) were achieved by alternating different liquid gain materials. Finally, dynamic switching of vortex laser wavelengths in real-time was realized through an optofluidic vortex microlaser device. The findings provide a robust yet flexible approach for generating on-chip vortex sources with multiple dimensions, high tunability, and reconfigurability.

Structuring total angular momentum of light along the propagation direction with polarization-controlled meta-optics

Recent advances in wavefront shaping have enabled complex classes of Structured Light which carry spin and orbital angular momentum, offering new tools for light-matter interaction, communications, and imaging. Controlling both components of angular momentum along the propagation direction can potentially extend such applications to 3D. However, beams of this kind have previously been realized using bench-top setups, requiring multiple interaction with light of a fixed input polarization, thus impeding their widespread applications. Here, we introduce two classes of metasurfaces that lift these constraints, namely: i) polarization-switchable plates that couple any pair of orthogonal polarizations to two vortices in which the magnitude and/or sense of vorticity vary locally with propagation, and ii) versatile plates that can structure both components of angular momentum, spin and orbital, independently, along the optical path while operating on incident light of any polarization. Compact and integrated devices of this type can advance light-matter interaction and imaging and may enable applications that are not accessible via other wavefront shaping tools.

Creating complex forms of structured light typically requires bulky optics and multiple interactions with incident light. Here the authors demonstrate versatile control over light’s polarization and orbital angular momentum along the propagation direction with a single metasurface.

Ray-wave duality of electromagnetic fields: a Feynman path integral approach to classical vectorial imaging

We consider how vectorial aspects (polarization) of light propagation can be implemented and their origin within a Feynman path integral approach. A key part of this scheme is in generalizing the standard optical path length integral from a scalar to a matrix quantity. Reparametrization invariance along the rays allows a covariant formulation where propagation can take place along a general curve. A general gradient index background is used to demonstrate the scheme. This affords a description of classical imaging optics when the polarization aspects may be varying rapidly and cannot be neglected.

Focus issue introduction: Advanced Solid-State Lasers 2020

This Joint Issue of Optics Express and Optical Materials Express features 15 articles written by authors who participated in the international online conference Advanced Solid State Lasers held 13-16 October, 2020. This review provides a summary of the conference and these articles from the conference which sample the spectrum of solid state laser theory and experiment, from materials research to sources and from design innovation to applications.