Principles of electromagnetic waves in metasurfaces

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SCIENCE CHINA Physics, Mechanics & Astronomy
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SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 58, Issue 9: 594201(2015) https://doi.org/10.1007/s11433-015-5688-1

Principles of electromagnetic waves in metasurfaces

XianGang LUO*,?
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  • ReceivedMar 26, 2015
  • AcceptedMay 7, 2015
  • PublishedAug 4, 2015
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Abstract

Metasurfaces are artificially structured thin films with unusual properties on demand. Different from metamaterials, the metasurfaces change the electromagnetic waves mainly by exploiting the boundary conditions, rather than the constitutive parameters in three dimensional (3D) spaces. Despite the intrinsic similarities in the operational principles, there is not a universal theory available for the understanding and design of metasurface-based devices. In this article, we propose the concept of metasurface waves (M-waves) and provide a general theory to describe the principles of them. Most importantly, it is shown that the M-waves share some fundamental properties such as extremely short wavelength, abrupt phase change and strong chromatic dispersion, which make them different from traditional bulk waves. It is shown that these properties can enable many important applications such as subwavelength imaging and lithography, planar optical devices, broadband anti-reflection, absorption and polarization conversion. Our results demonstrated unambiguously that traditional laws of diffraction, refraction, reflection and absorption should be revised by using the novel properties of M-waves. The theory provided here may pave the way for the design of new electromagnetic devices and further improvement of metasurfaces. The exotic properties of metasurfaces may also form the foundations for two new sub-disciplines called “subwavelength surface electromagnetics” and “subwavelength electromagnetics”.


Funded by

HU ChengGang

WANG YanQin

and MA XiaoLiang are acknowledged.

GAO Ping

WANG ChangTao

HUANG Cheng

National Program on Key Basic Research Project(2013CBA01700)

National Natural Science Foundation of China . Helpful discussions with PU MingBo(61138002)

LI Xiong

ZHAO ZeYu


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    Figure 1

    (Color online) Boundary conditions at the interface between two media (a) and a slab embedded between the two half spaces (b).

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    Figure 2

    (Color online) Schematic of the two kinds of M-waves. (a) kx< k0, (b) kx>k0. The upper and bottom layers are assumed as air.

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    Figure 3

    (Color online) Schematic of the extremely short-wavelength of different M-waves. (a) Wave in free space. (b) M-waves propagating through and (c–e) along the surfaces.

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    Figure 4

    (Color online) Schematic of the phase modulation schemes. (a) SPP in nano-slits. (b) M-waves with imaginary impedances. (c) Anisotropic antenna array for linear polarization. (d) Metasurface for circular polarization. (e) Spin-Hall effect in catenary structure. (f) Combination of anti-reflective structure with phase shift structure.

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    Figure 5

    (Color online) Applications of dispersion in M-waves. (a) Broadband anti-reflections. (b) Broadband perfect absorption. (c) Broadband polarization conversion. (d) Broadband spin-orbit interaction.

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    Figure 6

    (Color online) A simple model of plasmonic imaging lithography.

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    Figure 7

    (Color online) Schematic of the development of sub-diffraction technologies. The references [a-i] correspond to refs. [24–26, 72–77].

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    Figure 8

    (Color online) Breaking the near-field diffraction limit using plasmonic lens. (a) Schematic of the far-field and near-field diffraction limit. (b) Imaging contrast for plasmonic lens with different working distances and resolution. Inset shows the schematic of the plasmonic lens.

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    Figure 9

    (Color online) Schematic of the three generations of optical lenses.

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    Figure 10

    (Color online) (a) Comparison of metasurface with traditional components. (b) Photograph of the thin film metasurface lens. Inset shows the surface profile. (c) Focal spots for red light (left) and white (right) light.

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    Figure 11

    (Color online) Active metasurface for beam scanning in the microwave frequency. The overall thickness of the antenna is 3.89 mm, and the operational frequency is designed to be 5.4 GHz. The mean insertion loss is less than 4.5 dB.

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    Figure 12

    (Color online) Far-field super-resolution based on metasurface. (a) Diffraction limit for telescope. (b) Schematic of the experimental setup. The inset shows the phase distribution of the metasurface. Gray regions and white regions indicate 0 and π, respectively. (c) Experimental results for a circular hole at wavelength of l =532 nm. (d) Simulation results for a triangular hole.

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    Figure 13

    (Color online) Exchange between the propagating waves and M-waves. (a) Schematic of the principle. (b) Excitation of M-wave by propagating wave. (c) Conversion of the M-wave to propagating wave.

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    Figure 14

    (Color online) Roadmap for electromagnetic absorbers.

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    Figure 15

    (Color online) (a) Optical transmittance for the optical-transparent absorber. Inset shows the photograph. (b) Microwave absorption. Using flexible material shown in the inset (areal density < 0.5 kg/m2), ultrathin microwave absorber was obtained, while keeping the reflection in 1–12 GHz less than 10 dB for incidence angle up to 45°. (c) Reflectance and (d) transmission of the second sample. Inset shows the photograph of the sample. (e) Photograph and scanning electron microscope (SEM) of the third sample. (f) Reflection measured at different temperatures.

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    Figure 16

    (Color online) Equivalences in the bandwidth limitations on perfect absorbers and waveplates. (a) Coherent perfect absorber and perfect absorber, (b) coherent perfect rotation and perfect waveplates.

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    Figure 17

    (Color online) (a) Ultrathin (0.2 mm) conformal absorber. (b) Flexible ultrathin broadband absorber. (c) Schematic of the elastic metasurface. (d) Spectral transmittances for different dimensions. The length and width of the Aluminum patches are kept as 400 nm, while the periods (Px and Py) are varying from 490 nm to 510 nm.

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    Figure 18

    (Color online) Comparison of metamaterials with metasurfaces. (a) Realization of metasurface cloak by utilizing the MLRR. (b) Perfect metasurface lens. (c) Curved metasurface vs. traditional zero index material.

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