Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. This class of micro- and nano-structured artificial media have attracted great interest during the past 15 years and yielded ground-breaking electromagnetic and photonic phenomena. However, the high losses and strong dispersion associated with the resonant responses and the use of metallic structures, as well as the difficulty in fabricating the micro- and nanoscale 3D structures, have hindered practical applications of metamaterials. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response (e.g. scattering amplitude, phase, and polarization), mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

A review of metasurfaces: physics and applications.

Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response, mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

A review of metasurfaces: physics and applications

During the past few years, metasurfaces have been used to demonstrate optical elements and systems with capabilities that surpass those of conventional diffractive optics. Here, we review some of these recent developments, with a focus on dielectric structures for shaping optical wavefronts. We discuss the mechanisms for achieving steep phase gradients with high efficiency, simultaneous polarization and phase control, controlling the chromatic dispersion, and controlling the angular response. Then, we review applications in imaging, conformal optics, tunable devices, and optical systems. We conclude with an outlook on future potentials and challenges that need to be overcome.

https://www.degruyter.com/document/doi/10.1515/nanoph-2017-0129/pdf

A review of dielectric optical metasurfaces for wavefront control

Active modulation of electromagnetically induced transparency analogue in terahertz hybrid metal-graphene metamaterials

The heterostructure of two-dimensional (2D) materials are promising and useful in the field of surface plasmon resonance (SPR) biochemical sensors. To enhance the sensitivity, we design a novel SPR biochemical sensor by using heterostructures of few-layer black phosphorus (BP) and graphene/transition metal dichalcogenides (TMDCs). The SPR biochemical sensor based on the different heterostructures of BP and graphene/TMDCs are analyzed, and the highest sensitivity with 279°/RIU for the heterostructure of BP and bilayer WSe2 is obtained. Moreover, the proposed biochemical sensor can be used to detect the analyte with different refractive index. The most prominent advantage of the proposed structure is its high sensitivity. The maximum sensitivity of our proposed SPR biochemical sensor is about 2.4 times of the conventional biochemical sensor. We believe that this biochemical sensor could find potential applications in chemical examination, medical diagnosis and biological detection.

Sensitivity enhancement by using few-layer black phosphorus-graphene/TMDCs heterostructure in surface plasmon resonance biochemical sensor

We present a dynamically wavelength tunable plasmonically induced transparency (PIT) planar device composed of periodically patterned graphene nanostrips for the mid-infrared region The PIT effect can be achieved by a single layer of graphene nanostrips for a fixed Fermi energy The PIT resonant wavelength can be dynamically tuned while maintaining PIT modulation strength, transmission peaks, and spectral line width by varying the Fermi energy of graphene without re-optimizing and re-fabricating the nanostructures A three-level plasmonic system is demonstrated to well explain the formation mechanism of the wavelength tunable PIT in the graphene nanostrips This work may offer a further step in the development of a compact tunable PIT device

Dynamically tunable plasmonically induced transparency in periodically patterned graphene nanostrips

We present the design specifications and in-depth analysis of a terahertz (THz) broadband cross-polarization converter composed of a single-layer metasurface. This device can convert linearly polarized light into its cross-polarization in transmission mode. Different from other polarization conversion devices, this effect results from the suppression and enhancement for different electric components. The broadband characteristic is also achieved by specific partial symmetries designed in the structure. The proposed polarization converter can aid in the development of novel plasmonic polarization devices, and can help to overcome certain limitations of the customary designs that have been proposed thus far.

Realization of broadband cross-polarization conversion in transmission mode in the terahertz region using a single-layer metasurface

Harnessing light for modern photonic applications often involves the control and manipulation of light polarization and phase. Traditional methods require a combination of multiple discrete optical components, each of which contributes to a specifi c functionality. Here, plasmonic metasurfaces are proposed that accomplish the simultaneous manipulation of polarization and phase of the transmitted light. Arbitrary spatial fi eld distribution of the optical phase and polarization direction can be obtained. The multifunctional metasurfaces are validated by demonstrating a broadband near-perfect anomalous refraction with controllable linear polarization through introducing a constant phase gradient along the interface. Furthermore, the power of the proposed metasurfaces is demonstrated by generating a radially polarized beam. The new degrees of freedom of metasurfaces facilitate arbitrary manipulation of light and will profoundly affect a wide range of photonic applications.

http://www.iop.cas.cn/xwzx/kydt/201512/P020151221348581978116.pdf

Simultaneous Control of Light Polarization and Phase Distributions Using Plasmonic Metasurfaces

We present a mid-IR highly tunable optical polarization converter composed of asymmetric graphene nanocrosses. It can convert linearly polarized light to circularly and elliptically polarized light or exhibit a giant optical activity at different wavelengths. The transmitted wavelength and polarization states can also be dynamically tuned by varying the Fermi energy of graphene, without reoptimizing and refabricating the nanostructures. This offers a further step in developing a controllable polarization converter.

Mid-infrared tunable optical polarization converter composed of asymmetric graphene nanocrosses

Metasurfaces, which are capable of generating structure and wavelength dependent phase shift, have emerged as promising means for controlling the wavefront of electromagnetic waves. Finding new ways to realize broadband frequency response as well as maintaining high conversion efficiency still requires research efforts. For the design of plasmonic metasurfaces, graphene represents an attractive alternative to metals due to its strong field confinement and versatile tunability. Here, a novel metasurface based on graphene is proposed to control the wavefront of light. Dynamically tunable anomalous refraction composed of periodically patterned graphene nanocrosses for circularly polarized waves is achieved in the infrared regime. Broadband properties of anomalous refraction are demonstrated by investigating different frequencies and incident angles. Moreover, the anomalous conversion efficiency can be dynamically tuned and remain as high in a broadband frequency range by varying the Fermi energy without reoptimizing the nanostructures. This work may offer a further step in the development of a tunable wavefront controlling device.

Ping Yu

Papers

Dynamically tunable plasmonically induced transparency in periodically patterned graphene nanostrips

Realization of broadband cross-polarization conversion in transmission mode in the terahertz region using a single-layer metasurface

Simultaneous Control of Light Polarization and Phase Distributions Using Plasmonic Metasurfaces

Mid-infrared tunable optical polarization converter composed of asymmetric graphene nanocrosses

Dynamically Tunable Broadband Infrared Anomalous Refraction Based on Graphene Metasurfaces