Strongly Coupled Plasmon Polaritons in Gold and Epsilon-Near-Zero Bifilms

Abstract

Epsilon-near-zero (ENZ) polaritons in a thin transparent conducting-oxide film exhibit a significant electric field enhancement and localization within the film at frequencies close to their plasma frequency, but do not propagate. Meanwhile, plasmon polariton modes in thin metallic films can propagate for several microns, but are more loosely confined in the metal. Here, we propose a strongly coupled bilayered structure of a thin gold film on a thin indium tin oxide (ITO) film that supports hybrid polariton modes. We experimentally characterize the dispersion of these modes and show that they have propagation lengths of 4−8 μm while retaining mode confinement greater than that of the polariton in gold films by nearly an order of magnitude. We study the tunability of this coupling strength by varying the thickness of the ITO film and show that ultrastrong coupling is possible at certain thicknesses. The unusual linear and nonlinear optical properties of ITO at ENZ frequencies make these bifilms useful for the active tuning of strong coupling, ultrafast switching, and enhanced nonlinear interactions at near-infrared frequencies.

Interactions of Fundamental Mie Modes with Thin Epsilon-near-Zero Substrates

“…A comprehensive investigation of the nonlinear responses of these samples is beyond the scope of this work and is the subject of future research. We note that the speed of modification of the transmittance in our strongly coupled system of a-Si and ITO is at least one order of magnitude higher than the previously reported modification speeds of systems based on bare silicon. , In addition, the nonlinear response of the Si-ENZ-based metasurfaces can be further enhanced by using ITO layers of critical thickness . The nonlinear response of an array of dielectric metasurface on a 33 nm ITO, where the EDR and the MDR both spectrally overlap at the ENZ region of the ITO layer, has been recently reported .…”

Three-wave mixing experiments in indium–tin–oxide thin-films with no phase matching

“…These unique properties make ENZ materials, such as indium tin oxide (ITO), useful for a variety of applications [2]. For example, ITO's nonlinear properties can be used to tune its refractive index in useful ways [3]. Furthermore, ENZ modes and surface plasmon polariton modes supported by these ENZ materials demonstrate substantial field enhancement within the material [4,5].…”

“…However, by using low-index media like ENZ materials, we can satisfy phase-matching requirements for multiple input and output beam configurations, enabling more flexible and compact nonlinear devices. Due to the low index near the zero-epsilon wavelength (where nonlinearities arise), ENZ materials relax traditional phase-matching constraints, which can be exploited to facilitate nonlinear interactions and miniaturize nonlinear devices [3]. Therefore, ENZ materials such as ITO are promising for use in integrated devices.…”

Engineering the Infrared Optical Response of Plasmonic Structures with ϵ‐Near‐Zero III‐V Semiconductors

“…The free carriers oscillations cancel the permittivity at the plasma frequency, i.e., the metal/insulator transition frequency. ENZ materials include i) semiconductors (SCs) such as transparent conducting oxides (aluminum-doped zinc, [17] tin-doped indium, [18] gallium-doped zinc [19] oxides), and III-V SCs (GaAs, [20] AlGaAs/GaAs/AlGaAs quantum wells [5] ), ii) noble metals (Au and Ag [21] ), iii) polar dielectrics (SiC [7,22] ), iv) transition metal nitrides (TiN [23] ), v) correlated metals [24] (CaVO 3 , SrVO 3 ), as well as vi) artificially-designed ENZ, e.g., metamaterials [6] and hyperbolic materials. [25] The dielectric permittivity ϵ(𝜔) is related to the plasma frequency through the following Equation (1):…”