Rongzhen Li

Ultra-thin circular polarization analyzer based on the metal rectangular split-ring resonators

We propose an ultra-thin metasurface of the metal rectangular split-ring resonators (MRSRR) array which can modulate and analyze the wavefront of circularly polarized light efficiently. An incident circularly polarized light could be converted into the corresponding cross-polarized light which would be bent to ± 23° at a wavelength of 808 nm for the normal incidence. And a linearly polarized light would be decomposed into two lights of left and right-handed circular polarizations in the directions of ∓23° respectively. These phenomena have also been observed at 1200 nm with different geometric parameters. And these results depend on controlling the optical-axis profile of the resonators in a subwavelength scale by precisely modulating two degrees of freedom in our nanostructures.

Ultra-thin optical vortex phase plate based on the metasurface and the angular momentum transformation

The ultra-thin optical vortex phase plate (VPP) has been designed and investigated based on the metasurface of the metal rectangular split-ring resonators (MRSRRs) array. The circularly polarized incident light can convert into corresponding cross-polarization transmission light, and the phase and the amplitude of cross-polarization transmission light can be simultaneously governed by modulating two arms of the MRSRR. The MRSRR has been arranged in a special order for forming an ultra-thin optical VPP that can covert a plane wave into a vortex beam with a variety of the topological charges, and the transformation between spin angular momentum (SAM) and orbital angular momentum (OAM) has been discussed in detail. The multi-spectral characteristics of the VPP have also been investigated, and the operating bandwidth of the designed VPP is 190 nm (in the range of 710–900 nm), which enable a potential implication for integrated optics and vortex optics.

Plasmonics metalens independent from the incident polarizations.

An ultra-thin, planar, broadband metalens composed of L-shaped gap antennas on a thin gold film has been designed, which is suitable for both circular and X/Y linear polarizations focusing simultaneously. The phase discontinuity of the cross-polarized transmisson light can be manipulated by the length and width of the L-shaped gap antenna accurately. The designed planar metalens posses a strong focusing ability over a large wavelength range, and the size of the focus spot is in sub-wavelength scale. The focal lengths change from 13 to 7 um with incident wavelength from 750 to 1300 nm, and the cause of dispersion is explained and analyzed in detail. The designed metalens can work very well at a wide incident angles of 0~45°. Most importantly, its unique focusing ability that is independent of the incident polarizations will greatly promotes the practical applications and developments of the metasurfaces.

Broadband, high-efficiency, arbitrary focusing lens by a holographic dielectric meta-reflectarray

In this paper, a metalens based on the dielectric meta-reflectarray consisting of silicon nanorods in combination with a gold ground plane is proposed to realize an arbitrary focusing lens. We have demonstrated that the meta-reflectarray is served as a half-waveplate with near-unity reflectance and over 98% polarization conversion efficiency over a wavelength range from 1.5 to 1.6 μm for circularly polarized light incidences. We have also demonstrated that single spot and four-spaced spots focusing with more than 96% diffraction efficiency over 100 nm bandwidth can be realized by this metalens in the near infrared band just by controlling the reflection phases. The spatial phase distributions of the corresponding designed metalens can be determined via a computer-generated hologram method. Meanwhile, the desired phase can be simply obtained by modulating the orientation of the silicon nanorods. The proposed approach demonstrates a high-performance solution for creating low-cost and lightweight beam-shaping and beam-focusing devices at telecommunication wavelengths.

Circular Polarization Analyzer Based on the Combined Coaxial Archimedes’ Spiral Structure

We have designed a novel plasmonic lens for the circular polarization analyzer based on the combined coaxial Archimedes’ spiral structure which is composed of a Archimedes’ spiral slit (ASS) surrounded by coaxial Archimedes’ spiral gratings (ASG) on the both sides of the metal film. The designed structure is sensitive to polarization of the incident circularly polarized light, and it can realize the focusing effect under circular polarization illumination with specific handedness and defocusing effect under the other handed circular polarization illumination. This phenomenon of spin-dependent intensity distribution can be attributed to the presence of geometric phase effect of ASS. The simulated results show that the combination of the ASS and ASG has a higher efficiency and better performance than the traditional pure ASS.

L-shaped metasurface for both the linear and circular polarization conversions

A new type of optical polarization converter based on the L-shaped gold nanoantenna array supercell has been presented, which is suitable for both circular and X/Y linear polarization conversion simultaneously. Both the amplitude and phase of transmitted cross-polarization light can be modulated precisely by changing the lengths and widths of the L-shaped nanoantenna units. For circular or X/Y linear polarization incident lights, the corresponding cross-polarized lights can be obtained in the transmitted lights, and the corresponding bending angles of the cross-polarized lights can be modulated by the structures and the incident angles according to the generalized Snells law. The multi-spectral characteristics have also been investigated, in which the operating bandwidth of the designed optical polarization converter is 450 nm (in the range of 750 ~ 1200 nm).

Plasmonic focusing lens based on single-turn nano-pinholes array.

A miniature, simplified and planar plasmonic lens based on the circular array of nano-pinholes for on-axis beaming has been proposed and investigated systematically in the visible spectrum. Focusing properties of the designed plasmonic lens illuminated under circular polarized (CP) light for different radius of circular ring, filled with different dielectrics, with different numbers of pinholes have been investigated and analyzed in detail by finite element method (FEM). Our simulated results demonstrate such a miniature single-turn structure can also generate a totally centrosymmetric focusing spot under the CP illumination. Besides, by properly manipulating the filled dielectric and incident wavelengths, enhanced transmission, elongated depth of focus have also be realized, which can be used to modulate the transmitting fields effectively. Such a miniature and simplified plasmonic focusing lens can open up a vital path toward fiber-end planar photonic devices for biosensing and imaging.