An overview of the recent developments in the field of cylindrical vector beams is
provided. As one class of spatially variant polarization, cylindrical vector beams
are the axially symmetric beam solution to the full vector electromagnetic wave
equation. These beams can be generated via different active and passive methods.
Techniques for manipulating these beams while maintaining the polarization symmetry
have also been developed. Their special polarization symmetry gives rise to unique
high-numerical-aperture focusing properties that find important applications in
nanoscale optical imaging and manipulation. The prospects for cylindrical vector
beams and their applications in other fields are also briefly discussed.

Cylindrical vector beams: from mathematical concepts to applications

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Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

Metasurfaces are planar structures that locally modify the polarization, phase and amplitude of light in reflection or transmission, thus enabling lithographically patterned flat optical components with functionalities controlled by design. Transmissive metasurfaces are especially important, as most optical systems used in practice operate in transmission. Several types of transmissive metasurface have been realized, but with either low transmission efficiencies or limited control over polarization and phase. Here, we show a metasurface platform based on high-contrast dielectric elliptical nanoposts that provides complete control of polarization and phase with subwavelength spatial resolution and an experimentally measured efficiency ranging from 72% to 97%, depending on the exact design. Such complete control enables the realization of most free-space transmissive optical elements such as lenses, phase plates, wave plates, polarizers, beamsplitters, as well as polarization-switchable phase holograms and arbitrary vector beam generators using the same metamaterial platform.

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Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission

This Review article provides an overview of the fundamental origins and important applications of the main spin–orbit interaction phenomena in modern optics that play a crucial role at subwavelength scales. Light carries both spin and orbital angular momentum. These dynamical properties are determined by the polarization and spatial degrees of freedom of light. Nano-optics, photonics and plasmonics tend to explore subwavelength scales and additional degrees of freedom of structured — that is, spatially inhomogeneous — optical fields. In such fields, spin and orbital properties become strongly coupled with each other. In this Review we cover the fundamental origins and important applications of the main spin–orbit interaction phenomena in optics. These include: spin-Hall effects in inhomogeneous media and at optical interfaces, spin-dependent effects in nonparaxial (focused or scattered) fields, spin-controlled shaping of light using anisotropic structured interfaces (metasurfaces) and robust spin-directional coupling via evanescent near fields. We show that spin–orbit interactions are inherent in all basic optical processes, and that they play a crucial role in modern optics.

Spin-orbit interactions of light

Bound states in the continuum (BICs) are waves that remain localized even though they coexist with a continuous spectrum of radiating waves that can carry energy away. Their very existence defies conventional wisdom. Although BICs were first proposed in quantum mechanics, they are a general wave phenomenon and have since been identified in electromagnetic waves, acoustic waves in air, water waves and elastic waves in solids. These states have been studied in a wide range of material systems, such as piezoelectric materials, dielectric photonic crystals, optical waveguides and fibres, quantum dots, graphene and topological insulators. In this Review, we describe recent developments in this field with an emphasis on the physical mechanisms that lead to BICs across seemingly very different materials and types of waves. We also discuss experimental realizations, existing applications and directions for future work. The fascinating wave phenomenon of ‘bound states in the continuum’ spans different material and wave systems, including electron, electromagnetic and mechanical waves. In this Review, we focus on the common physical mechanisms underlying these bound states, whilst also discussing recent experimental realizations, current applications and future opportunities for research.

Bound states in the continuum

We propose and demonstrate an all-polarization-maintaining (PM) high-power cylindrical vector beam (CVB) fiber laser based on the principle of mode superposition. The non-degenerated LPy 11a is generated from the oscillator with the maximum power of 11.9W, whose slope efficiency is 24.4%. Then the stable single TE01 vector beam is achieved by the superposition of LPy 11a and LPx 11b in an all-PM architecture, its output power is 3.1W and mode purity of 91.2%. Due to the all-PM architecture, our configuration is free of adjusting polarization controller (PC) and reliable during long-term operation. This laser could be used as a high-power CVBs source for a wide range of applications towards scientific research and industrial field.

High-power cylindrical vector beam fiber laser based on an all-polarization-maintaining structure.

Optical vortex fields with a tilted phase singularity line are associated with a tilted orbital angular momentum (OAM). In this Letter, we propose a method to generate optical vortex fields with arbitrary OAM orientation based on the time-reversal method, vectorial diffraction theory, and a 4Pi optical configuration. The ability to control the 3D OAM orientation may find applications in optical tweezing, light-matter interaction, and spin-orbital coupling.

Optical vortex fields with an arbitrary orbital angular momentum orientation.

Cylindrical vector beams (CVBs) have a wide range of applications owing to their particular polarization characteristics and optical field distributions. For the first time, an azimuthally polarized fiber laser without any polarization controller is proposed and demonstrated experimentally. The scheme is based on a self-designed ring-core fiber and transverse mode filter (TMF). The ring-core fiber can break the degeneracy of LP11 modes and make the TE01 mode propagate stably in the fiber laser. The TMF, which made from the ring-core fiber by depositing a layer of Aluminum on the cladding surface, can effectively suppress the modes other than TE01 mode. The fiber laser can stably operate at TE01 mode with a narrow 30dB linewidth of 0.18nm, which indicates the laser is polarization-maintained. This study opens a new avenue toward the true application of CVBs fiber lasers.

An all-fiber laser oscillating directly at single TE01 mode through ring-core fibers.

An erbium-doped fiber laser cavity design is demonstrated to produce radially and azimuthally polarized beams. A c-cut
calcite crystal is set within a three-lens telescope system in the laser cavity. Due to the birefringence of the crystal, radial
and azimuthal polarizations are focused to different foci. The ray behavior through the crystal is discussed in details with
birefringent ray tracing. By translating a collimation lens, one can select either the radial or the azimuthal polarization to
lase in the cavity. The maximum output power obtained is about 140 mW for both polarizations.

High power erbium doped fiber laser generating switchable radially and azimuthally polarized beams at 1.6 µm wavelength

In solid immersion lens (SIL) system, both propagating waves and evanescent waves contribute to the total field strength with different properties. By using diffractive optical element to modify the cylindrical vector incident beam, we study how the field strength changes when propagating (evanescent) waves are balanced against each other and the evanescent (propagating) waves dominate the field strength. The simulation results show that for radially polarized incident beam, the rate of slope of axial field strength v.s transverse field strength by evanescent waves contribution is greater than that by propagating waves contribution. With general cylindrical vector incident beams, increasing (the rotation angle of polarization from the radial direction) will also make the axial field strength decrease while the variation of the transverse field strength is small. These methods can be used to control the aspect ratio of three dimensions storage dot, which may find applications in near field optical data storage system.

Qiwen Zhan

Papers

High-power cylindrical vector beam fiber laser based on an all-polarization-maintaining structure.

Optical vortex fields with an arbitrary orbital angular momentum orientation.

An all-fiber laser oscillating directly at single TE01 mode through ring-core fibers.

High power erbium doped fiber laser generating switchable radially and azimuthally polarized beams at 1.6 µm wavelength

Beam shaping with high-NA cylindrical vector beam illumination in SIL systems