Experimental demonstration of tunable graphene-polaritonic hyperbolic metamaterial

Abstract

Tuning the macroscopic dielectric response on demand holds potential for actively tunable metaphotonics and optical devices. In recent years, graphene has been extensively investigated as a tunable element in nanophotonics. Significant theoretical work has been devoted on the tuning the hyperbolic properties of graphene/dielectric heterostructures, however, until now, such a motif has not been demonstrated experimentally. Here we focus on a graphene/polaritonic dielectric metamaterial, with strong optical resonances arising from the polar response of the dielectric, which are, in general, difficult to actively control. By controlling the doping level of graphene via external bias we experimentally demonstrate a wide range of tunability from a Fermi level of E F = 0 eV to E F = 0.5 eV, which yields an effective epsilon-near-zero crossing and tunable dielectric properties, verified through spectroscopic ellipsometry and transmission measurements.Spectral tunability is key for controlling light-matter interactions, critical for many applications including emission control, surface enhanced spectroscopy, sensing, and thermal control. Particularly in the subwavelength range, tuning plasmonic resonances has been essential in controlling color, typically achieved by controlling the size of plasmonic nanoparticles, antennas and metamaterials 1-4 . In obtaining a large range of spectral tunability, it is preferable to operate near an optical resonance rather than a broadband plasmonic response. Nevertheless, it is in general easier to tune a broadband optical response rather than a resonant one since resonances in nanophotonics typically entail subwavelength-scale geometrical features.From a very wide range of recently investigated metamaterials and heterostructures for spectral control, particular emphasis has been given to hyperbolic media, due to enhanced light-matter interactions arising from a larger range of wavenumbers available for propagating modes 5 . These media are in generally uniaxial and support a hyperbolic frequency dispersion given by the equation 3,6-8where ε o and ε e refer to the ordinary (in-plane) and extraordinary (out-of-plane) dielectric permittivity, respectively. Due to the different sign in ε o and ε e , upon fixing the frequency ω, the isofrequency diagram of the relevant electromagnetic modes opens up into a hyperbola, giving rise to a very large density of optical states, promising for waveguiding 9 , emission engineering and Purcell enhancement 1,2,10 thermal photonics 11 , lasing 12 , and imaging 13,14 . Particularly, near the epsilon-near-zero frequency crossing of either ε o or ε e , many exciting phenomena can be supported, the most prominent of which is light propagation with near-zero phase advance 15-17 . a) Present address:There has been significant effort in frequency-tuning of the optical response of hyperbolic metamaterials 6,18-20 . For this, particular interest holds the case of graphene, a wellstudied monolayer material for electronics 21 and in infrared photonics 22 . Namely...

Hyperbolic metamaterials: From dispersion manipulation to applications

“…The metasurfaces with HMMs have been utilized for the asymmetric transmission [103] and high-efficiency wave-front manipulation [104]. The research scope of HMMs also has been extended to the actively controlled structures with graphene and VO2 [105][106][107], in which the hyperbolic dispersion and the associated properties can be actively tuned by changing the external field. In addition, many interesting phenomena and properties have been discovered in active HMMs, including the enhanced nonlinear effect [108][109][110], enhanced magnetooptical effect [111][112][113][114] and topological edge states [115,116].…”

Distributed Feedback Laser Based on Tunable Photonic Hypercrystal

“…However, the feasibility of the proposed structure was considered in the analysis. In particular, similar graphene-based multilayer stacks have been experimentally demonstrated [ 31 , 42 ]. Additionally, the deposition process of active material deposition, e.g., Er-doped glass, may be realized by means of a compatible technology, e.g., RF magnetron sputtering [ 38 , 43 ].…”

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