Dispersion management of anisotropic metamirror for super-octave bandwidth polarization conversion

Abstract

Dispersion engineering of metamaterials is critical yet not fully released in applications where broadband and multispectral responses are desirable. Here we propose a strategy to circumvent the bandwidth limitation of metamaterials by implementing two-dimensional dispersion engineering in the meta-atoms. Lorentzian resonances are exploited as building blocks in both dimensions of the dedicatedly designed meta-atoms to construct the expected dispersion. We validated this strategy by designing and fabricating an anisotropic metamirror, which can accomplish achromatic polarization transformation in 4-octave bandwidth (two times of previous broadband converters). This work not only paves the way for broadband metamaterials design but also inspire potential applications of dispersion management in nano-photonics. Since it was firstly illustrated by the pronounced prism experiment of Isaac Newton, the roles of chromatic dispersion in the interactions between electromagnetic wave and matter are extensively explored. It has been widely accepted that dispersion management is crucial in constructing spectrometers 1 , superprisms 2 , achromatic lens systems 3 , analog and digital optical communication system 4 . Proper dispersion contributes not only to the dense wavelength division multiplexing (DWDM) system 5 , but also the generation of soliton waves 6 . Dispersion of natural materials is determined by the electronic and molecular energy levels, with limited tunability. In the last decades, metamaterial has emerged as revolutionary material offering unprecedented superiority for dispersion engineering, while its electromagnetic property is exclusively decided by the specific geometry and arrangement of artificial meta-atoms [7][8][9][10][11] . Nevertheless, the difficulties in manufacture impede the further development of bulk metamaterials. As two-dimensional metamaterials, metasurfaces relax the fabrication requirement and meanwhile provide plenty of exotic properties such as phase discontinuity and abnormal deflection [12][13][14] . Especially, the ability to manipulate the polarization of electromagnetic waves is sought-after for numerous applications 15 . The past decade has witnessed the flourish of metasurface as polarization transformers owing to the miniaturized dimension and higher efficiency compared to traditional wave plates [16][17][18][19][20][21] . Theoretical investigations elucidate that the maximal conversion efficiency through a single metasurface can increase to 100% after introducing a reflective plane 22 . However, the highly resonant nature of meta-atoms that force the electromagnetic waves undergo a phase change ultimately causes a small bandwidth around their design frequency, as a result of the general Kramers-Kronig relations 23 . A nascent strategy to circumvent the bandwidth limitation of polarization converters is dispersion management 15,24 . This concept was also widely exploited in perfect absorbers [25][26][27][28][29] and band-pass filters 30 . Strikingly, the absorption bandwidth ca...

Color display and encryption with a plasmonic polarizing metamirror

“…Interestingly, the blue curve in the inset spectrum reaches a sharp peak at the same wavelength, which indicates that a phase difference of 180° is achieved between the orthogonal linear polarizations (|Φ x − Φ y | = 180°). This result agrees well with the conclusions in previous works [29,31,35], which is also a requirement to reflect a CP light to its copolarization state at normal incidence.…”

Convolution Operations on Coding Metasurface to Reach Flexible and Continuous Controls of Terahertz Beams

“…A metasurface is formed by distributing subwavelength resonant particles with different geometries and materials on a 2D surface, and therefore is able to manipulate both amplitudes and phases of electromagnetic (EM) waves, enabling many extraordinary functionalities such as the polarization conversion,,13, 14, 15, 16, 17 perfect absorption,18, 19, 20 and amplitude and phase modulations 21, 22. The generalized Snell's law proposed in 200123 has sped up the development of metasurfaces in the past a few years, enabling a lot of interesting devices to manipulate microwaves,24, 25, 26 terahertz waves,27, 28 and visible lights 29, 30, 31…”

Ultra-wideband manipulation of electromagnetic waves by bilayer scattering engineered gradient metasurface

“…A more effective method to broaden working bandwidth is dispersion management which can approach the bandwidth-thickness limits. [32][33][34][35][36] In ref. 32, one-dimensional dispersion management was used to achieve polarization conversion with the bandwidth ratio over 3 : 1.…”

“…Subsequently, bandwidth ratio over 5 : 1 was achieved by 2D dispersion management. 33,34 Recently, a broadband metasurface for simultaneous thermal infrared invisibility and holographic illusion has been demonstrated.…”