Abstract
Miniaturized quarter-wave plate devices empower spin to orbital angular momentum conversion and vector polarization formation, which serve as bridges connecting conventional optical beam and structured light. Enabling the manipulability of additional dimensions as the complex polarization and phase of light, quarter-wave plate devices are essential for exploring a plethora of applications based on orbital angular momentum or vector polarization, such as optical sensing, holography, and communication. Here we propose and demonstrate the magnetic metamaterial quarter-wave turbines at visible wavelength to produce radially and azimuthally polarized vector vortices from circularly polarized incident beam. The magnetic metamaterials function excellently as quarter-wave plates at single wavelength and maintain the quarter-wave phase retardation in broadband, while the turbine blades consist of multiple polar sections, each of which contains homogeneously oriented magnetic metamaterial gratings near azimuthal or radial directions to effectively convert circular polarization to linear polarization and induce phase shift under Pancharatnum-Berry’s phase principle. The perspective concept of multiple polar sections of magnetic metamaterials can extend to other analogous designs in the strongly coupled nanostructures to accomplish many types of light phase-polarization manipulation and structured light conversion in the desired manner.
Highlights
It is typically difficult to simultaneously and effectively manipulate polarization and phase of light at nanoscale which is critical in ultra-compact integrated optics, because the optical anisotropy provided by naturally existing materials is generally too finite to significantly modulate light in deep-subwavelength space
The homogeneous magnetic metamaterial gratings are designed, fabricated, and characterized to confirm its functionality as a good quarter-wave plate (QWP), which will serve as the fundamental building blocks for constructing the spatial inhomogeneous magnetic metamaterial quarter-wave turbines
Magnetic resonances can be excited under transverse-magnetic (TM) illumination in this structure, where the magnetic field of the incident beam is parallel with the metal stripes
Summary
Miniaturized quarter-wave plate devices empower spin to orbital angular momentum conversion and vector polarization formation, which serve as bridges connecting conventional optical beam and structured light. We propose and demonstrate the magnetic metamaterial quarter-wave turbines at visible wavelength to produce radially and azimuthally polarized vector vortices from circularly polarized incident beam. The relationship between the polarization and phase variation of the transmitted beam can be described by the space-domain geometric phase—‘the Pancharatnam-Berry phase’[23,24], discovered by the pioneer scientists[25,26,27,28,29] Based on this principle, the anisotropic optical element, termed as the Pancharatnam-Berry phase Optical Element (PBOE), can be used to induce the designated phase and polarization manipulations. The vector polarization distributions of the produced vortices can be conveniently tuned azimuthally or radially by switching the spin of the incident CP beam or the turbine rotation direction
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