Enhanced high-order diffractions which are spatially dispersive are desirable in such as spectroscopy studies, thin-film solar cells, etc. Conventionally, the dielectric gratings can be used to realize the enhanced diffraction, but the facets are usually rugged and optically thick (~μm). Plasmonic materials may exhibit unprecedented ability for manipulating light. Nonetheless, much interest has been focused on the subwavelength metasurfaces working in the zero-order regime. Here, we show that ultra-broadband and strongly enhanced diffraction can be achieved with the super-wavelength metasurfaces. For the purpose, we employ symmetric or asymmetric metal patches on a ground metal plane, which support the localized oscillation of free electrons and enhanced scattering of light. The zero-order reflection is suppressed, giving rise to an enhancement of first-order diffraction (50 ~ 95%) in an ultra-wide bandwidth (600 ~ 1500 nm). The proposed plasmonic structure is planar and ultra-thin (with an etching depth of only 80 nm), showing new potential for constructing compact and efficient dispersive elements.

Tri-layered metal films perforated with rectangle hole arrays of different orientations and separated by glass/air spacers have been studied theoretically and experimentally. The devices can rotate the polarization of the incident light by 90o with high efficiency and wide bandwidth in the near-infrared and microwave regions. The high-efficiency and wide bandwidth polarization rotation can be ascribed to the near-field coupling regime rather than the Fabry-Perot resonance according to the investigation of the difference between the two regimes.

Single-layered metasurfaces are easier to fabricate than multi-layered ones but suffering from low efficiency and/or narrow bandwidth for transmissive polarization rotation. In this work, we propose a single-layered metasurface which can realize 90° polarization rotation with high efficiency, wide bandwidth, and ultra-high polarization conversion ratio in transmission mode. In addition, the single-layered metasurface can also be used as an efficient and wideband polarizer, which couples the two orthogonal electric components of incident light to the transmitted polarization.

Surface plasmon-polaritons (SPPs)-based waveguides, especially hybrid plasmonic nanowires, which have attracted extensive interests due to easy fabrication, high transmittance, subwavelength mode confinement and long propagation distance, are appropriate platforms for enhancing the interaction with graphene. Considering that graphene is a two-dimensional (2D) material with surface conductivity, it is important to enhance the in-plane electrical components parallel to graphene. Here, we propose a tunable graphene optical modulator based on arrayed hybrid plasmonic nanowires, utilizing strong subwavelength confinement of gap-surface plasmonic modes (GSPMs) and near-field coupling in the periodic metasurface structure to enhance effective light-matter interactions. The modulator has a typical modulation depth (MD) of 4.7 dB/μm, insertion loss (IL) of 0.045 dB/μm, and a broadband response. The modulation performance can be further optimized, achieving MD of 16.7 dB/μm and IL of 0.17 dB/μm. Moreover, with the optimized modulator, the 3 dB bandwidth can reach 200 GHz. The energy consumption of modulator is about 0.86 fJ/bit. Our design exhibits fascinating modulation performance, fabrication compatibility and integration potential. It may inspire the schematic designs of graphene-based plasmonic modulator and pave a way to the application of 2D materials-involved optoelectronic devices.

Traditional metamaterial systems usually own a low Q factor due to the strong absorption and radiation loss. Fano resonances in ultrathin metasurfaces provide an efficient method for solving the issue. In this work, we theoretically and experimentally study the trapped-mode resonance in rectangular-hole dimers with broken symmetry. Compared to the asymmetric particle dimers that have been widely investigated, the asymmetric hole dimers in freestanding metal screens present an all-metallic platform for engineering the high-Q resonances. With the experiments, a significantly increased Q factor of ∼200 has been achieved in the microwave region. Numerical simulations show that, in comparison with the incident field, the hole electric field (and intensity) can be increased by ∼127 times (and ∼16 000 times). Moreover, the evolution characteristic of the trapped-mode resonance with the structural parameters has been studied systematically. The inversely quadratic relationship between the Q factor and asymmetric parameter, proposed primarily for the particle dimers [Koshelev et al., Phys. Rev. Lett. 121, 193903 (2018)], is found to work well for the asymmetric hole dimers.

Active plasmonic modulators with high modulation depth, low energy consumption, ultra-fast speed, and small footprint are of interest and particular significance for nanophotonics and integrated optics. Here by constructing a transverse-electric (TE) plasmonic mode and maximizing the in-plane component localized on the graphene surface, we propose a high-performing plasmonic modulator based on a graphene/split ring-like plasmonic waveguide (SRPW) system with a record high modulation depth (20.46 dB/µm) and suppressed insertion loss (0.248 dB/µm) at telecom wavelength 1310 nm, simultaneously possessing pronounced advantage in broadband ability (800-1650 nm) and superior electrical performance with energy consumption of 0.43 fJ/bit and modulation speed of 200 GHz. This innovative design provides a novel approach and idea for enhancing the interaction between light and matter in the waveguide system and will certainly inspire new schemes for the development of on-chip integrated optoelectronic devices.