A chiral plasmonic lens (CPL) suitable for circularly polarized light is proposed; it consists of multiple concentric grooves surrounded by two Archimedes-spiral distributed arrays of rectangular nanoslits milled into a gold film. We demonstrate both theoretically and numerically that the proposed CPL can convert an incident circular polarization beam with prescribed chirality into a long centrosymmetric focus with a size beyond the diffraction limit, but the circularly polarized one with the opposite chirality cannot be transmitted and focused by the same CPL due to the chirality of the proposed structure. Depending on the design parameters, an optical needle or optical tube in the focal field can be achieved; the attainable focus has a full-width at half-maximum of 0.43λ0 and an elongated depth of focus of 2.95λ0 with λ0 denoting the wavelength of illumination light.
A chiral plasmonic lens (CPL) suitable for circular polarization analyzer is designed and numerically investigated. It consists of two arrays of rectangular nanoslits milled into a gold film along Archimedes spirals. We demonstrate both theoretically and numerically that the designed structure can convert an incident circularly polarized light beam with prescribed chirality into a Bessel-like distributed focus, but the circularly polarized one with the opposite chirality cannot be transmitted and focused by the same CPL due to the alternative chirality. Further, three-dimensional finite-difference time-domain (FDTD) simulations show that an ultrahigh extinction ratio up to ten thousands of the CPL is numerically achieved with a device less than 10 λspp, which is two orders higher than that of a conventional plasmonic circularization analyzer with single Archimedes-spiral groove. The designed structure can be widely used in miniature polarimeter and detection of spin angular momentum.
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