Bi-functional polarization conversion in hybrid graphene-dielectric metasurfaces

Wang

2020

Nanomaterials

In this paper, a tunable terahertz dielectric metasurfaces consisting of split gap bars in the unit cell is proposed and theoretically demonstrated, where the sharp high-quality Fano resonance can be achieved through excitation of quasi-bound states in the continuum (quasi-BIC) by breaking in-plane symmetry of the unit cell structure. With the structural asymmetry parameter decreasing and vanishing, the calculated eigenmodes spectra demonstrate the resonance changes from Fano to symmetry-protected BIC mode, and the radiative quality factors obey the inverse square law. Moreover, combining with graphene monolayer and strontium titanate materials, the quasi-BIC Fano resonance can be tuned independently, where the resonance amplitude can be tuned by adjusting the Fermi level of graphene and the resonance frequency can be tuned by controlling the temperature of strontium titanate materials. The proposed structure has numerous potential applications on tunable devices including modulators, switches, and sensors.

Section: Introductionmentioning

confidence: 99%

Tunable Bound States in the Continuum in All-Dielectric Terahertz Metasurfaces

Wang

2020

Nanomaterials

“…For example, a hybrid graphene–dielectric metasurface that can switch between a half‐wave plate and a quarter‐wave plate by applying external biasing voltage was proposed. [ 19 ] In addition, some devices can transform between a broadband absorber and a narrowband absorber. Song et al put forward an absorber with tunable bandwidth by utilizing the characteristic that VO 2 can switch between the amorphous state and the crystalline state.…”

Section: Introductionmentioning

confidence: 99%

“…This makes metamaterials evolve from passive and lack of real-time tuning to enabling active control of the operating frequency, amplitude, phase, or other properties. Although tunable materials are added, these metamaterials are often limited to one kind of functional tuning.Recently, some devices utilizing graphene, [18][19][20][21] vanadium dioxide (VO 2 ) in refs. [22][23][24][25][26][27][28], and Ge 2 Sb 2 Te 5 (GST) in ref.…”

mentioning

confidence: 99%

“…Recently, some devices utilizing graphene, [18][19][20][21] vanadium dioxide (VO 2 ) in refs. [22][23][24][25][26][27][28], and Ge 2 Sb 2 Te 5 (GST) in ref.…”

mentioning

confidence: 99%

“…Comparisons between this work and reported switchable bifunctional metasurfaces.Quarter-wave plate and half-wave plate[19] Graphene 1-1.1 THz: Ellipticity ≤ -0.9 0.93-1.12 THz: PCR ≥ 85%…”

mentioning

confidence: 99%

See 2 more Smart Citations

A Thermally Switchable Bifunctional Metasurface for Broadband Polarization Conversion and Absorption Based on Phase‐Change Material

Advanced Photonics Research

Liu

et al. 2022

Terahertz (THz) technology has attracted more and more attention due to its wide application prospects in imaging, communication, spectroscopy, and other fields. [1] Thanks to the development of metamaterials and metasurfaces, terahertz functional devices such as absorbers, [2,3] polarizers, [4,5] and filters in refs. [6,7] have been greatly developed. Through elaborate design, one can get devices or structures with certain functions. However, once the structure of the metamaterial is determined and made, its function and performance will be fixed.To solve this problem, materials such as stretchable substrate, [8,9] graphene, [10,11] Dirac semimetal, [12,13] and phase-change material in refs. [14][15][16][17] that can be tuned by external pressure, thermal heating, applied current, or optical pumping are added to the design of metamaterials. This makes metamaterials evolve from passive and lack of real-time tuning to enabling active control of the operating frequency, amplitude, phase, or other properties. Although tunable materials are added, these metamaterials are often limited to one kind of functional tuning.Recently, some devices utilizing graphene, [18][19][20][21] vanadium dioxide (VO 2 ) in refs. [22][23][24][25][26][27][28], and Ge 2 Sb 2 Te 5 (GST) in ref. [29] to achieve dual functions have emerged. Among them, some have the function of switching between the quarter-wave plate and half-wave plate. For example, a hybrid graphene-dielectric metasurface that can switch between a half-wave plate and a quarter-wave plate by applying external biasing voltage was proposed. [19] In addition, some devices can transform between a broadband absorber and a narrowband absorber. Song et al. put forward an absorber with tunable bandwidth by utilizing the characteristic that VO 2 can switch between the amorphous state and the crystalline state. [22] Moreover, some studies combine polarization conversion and absorption into a single metasurface simultaneously. Song et al. proposed a bifunctional metasurface based on VO 2 to achieve broadband absorber and broadband polarization converter. [24] The design idea of this metasurface is to design a typical metal-insulator-metal (MIM) structure, and then add another three-layer structure of VO 2 -insulator-VO 2 on this structure. Through the phase transition of VO 2 , the two functions can be switched. Li et al. also adopted this design idea to realize the conversion between a broadband absorber and broadband polarization converter. [30]

Tunable Polarization‐Preserving Vortex Beam Generator Based on Diagonal Cross‐Shaped Graphene Structures at Terahertz Frequency

Advanced Optical Materials

Yang

et al. 2023

The vortex beams carrying orbital angular momentum (OAM) are of extreme importance for applications in communication, nanoscience, and optical micro‐manipulation. The development of dynamically tunable vortex beam generators with compact size is a critical step in the realization of vortex beam modulation and application. Here, a series of ultrathin OAM‐tunable polarization‐preserving vortex beam generators based on graphene metasurfaces are proposed, which offer a new scheme to generating vortex beams with variable topological charges at terahertz frequency. By introducing the diagonal cross‐shaped graphene structures, the abrupt phase shift range reaches 2π for linearly polarized incident light while maintaining the original polarization state. Planar spiral phase generators are theoretically constructed to convert beams with plane wavefront into beams with spiral phase. More importantly, the topological charges of the generated vortex beams can be dynamically tuned by the graphene Fermi energy in a broadband frequency range from 4.5 to 5.5 THz. This work provides a simple technology for the generation of vortex beams and the flexible modulation of the topological charge, which would inspire the application potential of the vortex beam.