Yuancheng Fan

An ultrathin twist-structure polarization transformer based on fish-scale metallic wires

This study theoretically and experimentally investigates the transmission properties of a metamaterial slab comprised of two layers of metallic fish-scale structure arrays and a sandwiched dielectric layer. Calculations show that the asymmetric transmission can be tuned by varying the slab thickness, due to near-field interlayer coupling. The spatial evolution of the electric field indicates that the twist structure functions as a perfect polarization transformer at certain frequencies. Measured transmission spectra are in good agreement with calculated results when material dissipation is considered.This study theoretically and experimentally investigates the transmission properties of a metamaterial slab comprised of two layers of metallic fish-scale structure arrays and a sandwiched dielectric layer. Calculations show that the asymmetric transmission can be tuned by varying the slab thickness, due to evanescent interlayer coupling. The spatial evolution of the local field inside the structure indicates that the slab functions as a perfect polarization transformer at certain frequencies in the manner of a waveguide twist. Measured transmission spectra are in good agreement with calculated results when material dissipation is considered.

Enhancing infrared extinction and absorption in a monolayer graphene sheet by harvesting the electric dipolar mode of split ring resonators

Optical extinction and absorption enhancement in the infrared range of a monolayer graphene sheet by patterning split ring resonators (SRRs) is studied. It is found that the electric mode is stronger in enhancing infrared extinction and absorption compared to the magnetic mode and other higher-order modes. We improve the infrared extinction of the SRR graphene sheet by increasing the graphene area ratio in the SRR unit cell design. With the increase of the graphene area ratio, the radiation ability of the electric dipolar mode and dissipation of graphene compete for a maximum infrared absorption of about 50%. The findings on enhancing infrared extinction and absorption of the graphene sheet by harvesting the electric dipolar mode may have potential applications in terahertz and infrared detection and modulation for graphene photonics and optoelectronics.

Subwavelength electromagnetic diode: One-way response of cascading nonlinear meta-atoms

We propose a scheme for subwavelength electromagnetic diode by employing cascading nonlinear meta-atoms. One-way response is conceptually demonstrated on a microwave transmission line comprising of three metallic ring resonators acting as meta-atoms and a varactor as the nonlinear medium inclusion. Experiments show that our implementation can operate simultaneously as forward diode and backward diode at different frequencies. A transmission contrast of up to 14.7 dB was achieved between forward and backward transmission. Subwavelength size of our diode should be useful for miniaturization of integrated optical nanocircuits.

Broadband negative refraction in stacked fishnet metamaterial

We demonstrate a scheme to utilize the stacked fishnet metamaterial for all-angle negative refraction and subwavelength imaging within a wide frequency range starting from zero frequency. The theoretical predictions are verified by the brute-force finite-difference-in-time-domain numerical simulations. The phenomena come from the negative evanescent coupling between the adjacent slab waveguides through the breathing air holes perforated on metal layers.

Nonlinear properties of meta-dimer comprised of coupled ring resonators

We experimentally and theoretically investigate the nonlinear electromagnetic properties of an on-chip metamaterial system comprised of two coupled ring resonators (CRRs) as meta-dimer and a varactor loaded in between them as nonlinear medium inclusion. The resonant frequency of the anti-symmetric coupling mode of CRRs is sensitive to the input power and can be tuned to an extremely low frequency as the induced voltage gradient loaded on the varactor is maximized when the mode is excited. Nonlinear responses, including the shift of resonant frequency as well as hysteresis effects, are demonstrated experimentally in distinct ranges of input powers. The findings have potential applications in implementing subwavelength nonlinear components for integrated plasmonic nanocircuits or metactronics.

Mode propagation in a PT-symmetric gain?metal?loss plasmonic system

A novel gain?metal?loss plasmonic system with PT-symmetry is proposed and provides a new way of optical operation. Mode propagation is demonstrated by theoretical investigation of the dispersion map of the system and confirmed by simulating a case involving a dispersive gain and loss medium with a commercial finite-element solver. These results are beneficial for optical signal processing on a subwavelength scale.

Near-diffraction-limited focusing with gradient high-impedance metasurface

We propose a new technique for wavefront manipulation using a high-impedance metasurface made of a reflectarray containing gradient mushroom-shaped elements, which provide a full-range phase shift for accomplishing the manipulation. The reflection phase of the high-impedance metasurface shows a linear discontinuity dependence on the sizes of the unit elements. Near-diffraction-limited focusing and a high efficiency of 80% were achieved by modulating the reflection phase using the gradient high-impedance metasurface. The experimental results and the theoretical simulation were in good agreement. The proposed gradient high-impedance metasurface can be employed for highly effective wavefront engineering.