Abstract
We propose a tunable circular polarization analyzer based on a graphene-coated spiral dielectric lens. Spatially separated solid dot shape (or donut shape) field can be achieved if the geometric shape of analyzer and incident circular polarization possess the opposite (or same) chirality. Moreover, distinct from the narrow working bandwidth of a traditional circular polarization analyzer, the focusing and defocusing effects in the analyzer are independent of the chemical potential of graphene, and depend only on the dielectric permittivities and the grating occupation ratio. Combined with the strong tunability of graphene plasmons, the operation wavelength of analyzer can be tuned by adjusting the graphene chemical potential without degrading the performance. The proposed analyzer could be used in applications in chemistry or biology, such as analyzing the physiological properties of chiral molecules based on circular polarization.
Highlights
When a circularly polarized beam is focused onto axially symmetric plasmonic structure, the entire beam is transverse magnetic (TM) polarized with respect to the interface, enabling surface plasmon excitation from all directions and homogeneous plasmon focusing through interferences of these plasmon waves
A strongly confined solid spot will be obtained when the geometric phase produced by the spiral dielectric gratings cancels out the vortex wavefront of circularly polarized illumination [1]
An electric field with donut shape emerges due to the superposition of geometric phase and the vortex wavefront
Summary
When a circularly polarized beam is focused onto axially symmetric plasmonic structure, the entire beam is transverse magnetic (TM) polarized with respect to the interface, enabling surface plasmon excitation from all directions and homogeneous plasmon focusing through interferences of these plasmon waves. A strongly confined solid spot will be obtained when the geometric phase produced by the spiral dielectric gratings cancels out the vortex wavefront of circularly polarized illumination (spiral structure and incident light owe opposite chirality) [1].
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