Electromagnetic metasurface

An electromagnetic metasurface refers to a kind of artificial sheet material with sub-wavelength thickness and electromagnetic properties on demand. As shown in the review article given by Capasso et al., metasurfaces could be either structured or not structured with subwavelength-scaled patterns in the horizontal dimensions.[1]

In the electromagnetic theory, metasurfaces could modulate the behaviors of electromagnetic waves through the specific boundary conditions, rather than the constitutive parameters in the three dimensional (3D) space, which is however commonly exploited in natural materials and metamaterials. Sometimes metasurfaces refer to also the two-dimensional counterparts of metamaterials.[2]

Definitions

The followings are several kinds of definitions made by researchers:

1, “An alternative approach that has gained increasing attention in recent years deals with one- and two-dimensional (1D and 2D) plasmonic arrays with subwavelength periodicity, also known as metasurfaces. Due to their negligible thickness compared to the wavelength of operation,metasurfaces can (near resonances of unit cell constituents) be considered as an interface of discontinuity enforcing an abrupt change in both the amplitude and phase of the impinging light”.[3]

2, “Our results can be understood using the concept of a metasurface, a periodic array of scattering elements whose dimensions and periods are small compared with the operating wavelength”.[4]

3, “Metasurfaces based on thin films”. A highly absorbing ultrathin film on a substrate can be also considered as a metasurface, with properties not occurring in natural materials.[1] Following this definition, the thin metallic films such as that in superlens are also early type of metasurfaces.[5]

History

The research of artificial electromagnetic metasurfaces has a long history. Early in 1902, Robert W. Wood found that the reflection spectra of subwavelength metallic grating had dark area. This unusual phenomenon was named Wood’s anomaly, and led to the discovery of surface plasmon polariton (SPP),[6] a particular electromagnetic wave excited at metal surfaces. Subsequently, another important phenomenon, the Levi-Civita relation,[7] was introduced, which states that a subwavelength-thick film can result in a dramatic change of electromagnetic boundary conditions.

Generally speaking, metasurfaces could include some traditional concepts in the microwave spectrum such as frequency selective surface (FSS), impedance sheet and even Ohmic sheet. In the microwave regime, the thickness of these metasurfaces can be much smaller than the wavelength of operation (for example, 1/1000 of the wavelength), since the skin depth could be extremely small for highly conductive metals. Recently, some novel phenomena such as ultra-broadband coherent perfect absorption were demonstrated. The results are astonishing since a 0.3 nm thick film could absorb all electromagnetic wave across the RF, microwave, and even terahertz frequencies.[8][9]

In the optical applications, an anti-reflective coating could also be regarded as a simple metasurface, as firstly observed by Lord Rayleigh.

In recent years, there are some new metasurfaces, which are shown as follows:

  1. Plasmonic metasurfaces.[2][3][10]
  2. Metasurfaces based on geometric phase.[11][12]
  3. Metasurfaces based on impedance sheet.[13][14]

Applications

One the most important applications of metasurfaces is to control the wavefront of electromagnetic waves by imparting local, gradient phase shift to the incoming waves, which leads to a generalization of the ancient laws of reflection and refraction.[11] In this way, metasurfaces can be made as a planar lens,[15] vortex generator,[16] beam deflector, axicon and so on.[12][17]

Beside the gradient metasurface lenses, Metasurface-based superlenses offer another degree of controlling the wavefront by utilizing the evanescent waves. With surface plasmon in the ultrathin metallic layers, perfect imaging and super-resolution lithography could be enabled, which breaks the common assumption that all optical lens systems are limited by diffraction, a phenomenon termed diffraction limit.[18][19]

In addition, Metasurfaces can also find applications in electromagnetic absorbers, polarization converters and spectrum filters etc.

References

  1. 1 2 Yu, Nanfang; Capasso, Federico (2014). "Flat optics with designer metasurfacces". Nat. Mater. 13: 139–150. doi:10.1038/nmat3839.
  2. 1 2 Zeng, S.; et al. (2015). "Graphene-gold metasurface architectures for ultrasensitive plasmonic biosensing". Advanced Materials. 27: 6163–6169. doi:10.1002/adma.201501754.
  3. 1 2 Pors, Anders; Bozhevolnyi, Sergey I. (2013). "Plasmonic metasurfaces for efficient phase control in reflection". Optics Express. 21: 27438. Bibcode:2013OExpr..2127438P. doi:10.1364/OE.21.027438.
  4. ↑ Li, Ping-Chun; Zhao, Yang; Alu, Andrea; Yu, Edward T. (2011). "Experimental realization and modeling of a subwavelength frequency-selective plasmonic metasurface". Appl. Phys. Lett. 99: 221106. Bibcode:2011ApPhL..99c1106B. doi:10.1063/1.3614557.
  5. ↑ Pendry, J. B. (2000). "Negative Refraction Makes a Perfect Lens" (PDF). Physical Review Letters. 85 (18): 3966–9. Bibcode:2000PhRvL..85.3966P. doi:10.1103/PhysRevLett.85.3966. PMID 11041972.
  6. ↑ Wood, R. W. (1902). "On a remarkable case of uneven distribution of light in a diffraction grating spectrum". Proc. Phys. Soc. London. 18: 269–275. Bibcode:1902PPSL...18..269W. doi:10.1088/1478-7814/18/1/325.
  7. ↑ Senior, T. (1981). "Approximate boundary conditions". IEEE Trans. Antennas Propag. 29: 826–829. doi:10.1109/tap.1981.1142657.
  8. ↑ Pu, M.; et al. (17 January 2012). "Ultrathin broadband nearly perfect absorber with symmetrical coherent illumination". Optics Express. 20 (3): 2246–2254. Bibcode:2012OExpr..20.2246P. doi:10.1364/oe.20.002246.
  9. ↑ Li, S.; et al. "Broadband Perfect Absorption of Ultrathin Conductive Films with Coherent Illumination: Super Performance of Electromagnetic Absorption". arXiv:1406.1847Freely accessible.
  10. ↑ Verslegers, Lieven; Fan, Shanhui (2009). "Planar Lenses Based on Nanoscale Slit Arrays in a Metallic Film". Nano Lett. 9: 235–238. doi:10.1021/nl802830y.
  11. 1 2 Yu, Nanfang; Genevet, Patrice; Kats, Mikhail A.; Aieta, Francesco; Tetienne, Jean-Philippe; Capasso, Federico; Gaburro, Zeno (2011). "Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction". Science. 334: 333–337. Bibcode:2011Sci...334..333Y. doi:10.1126/science.1210713.
  12. 1 2 Lin, Dianmin; Fan, Pengyu; Hasman, Erez; Brongersma, Mark L. (2014). "Dielectric gradient metasurface optical elements". Science. 345: 298–302. Bibcode:2014Sci...345..298L. doi:10.1126/science.1253213.
  13. ↑ Pfeiffer, Carl; Grbic, Anthony (2013). "Metamaterial Huygens' Surfaces: Tailoring Wave Fronts with Reflectionless Sheets". Phys. Rev. Lett. 110: 197401. arXiv:1206.0852Freely accessible. Bibcode:2013PhRvL.110b7401W. doi:10.1103/PhysRevLett.110.027401.
  14. ↑ Felbacq, Didier (2015). "Impedance operator description of a metasurface". Mathematical Problems in Engineering. 2015: 473079. doi:10.1103/10.1155/2015/473079.
  15. ↑ Aieta, Francesco; Genevet, Patrice; Kats, Mikhail; Yu, Nanfang; Blanchard, Romain; Gaburro, Zeno; Capasso, Federico (2012). "Aberration-free ultra-thin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces". Nano Letters. 12: 4932. doi:10.1021/nl302516v.
  16. ↑ Genevet, Patrice; Yu, Nanfang; Aieta, Francesco; Lin, Jiao; Kats, Mikhail; Blanchard, Romain; Scully, Marlan; Gaburro, Zeno; Capasso, Federico (2012). "Ultra-thin plasmonic optical vortex plate based on phase discontinuities". Applied Physics Letters. 100: 013101. doi:10.1063/1.3673334.
  17. ↑ Xu, T.; et al. (2008). "Plasmonic deflector". Opt. Express. 16: 4753. doi:10.1364/oe.16.004753.
  18. ↑ Luo, Xiangang; Ishihara, Teruya (2004). "Surface plasmon resonant interference nanolithography technique". Appl. Phys. Lett. 84: 4780. Bibcode:2004ApPhL..84.4780L. doi:10.1063/1.1760221.
  19. ↑ Fang, Nicholas; Lee, Hyesog; Sun, Cheng; Zhang, Xiang (2005). "Sub-Diffraction-Limited Optical Imaging with a Silver Superlens". Science. 308: 534–7. Bibcode:2005Sci...308..534F. doi:10.1126/science.1108759. PMID 15845849.
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