Ultrafast nonlinear dynamics of thin gold films due to an intrinsic delayed nonlinearity

Using long-range surface plasmon polaritons light can propagate in metal nano-scale waveguides for ultracompact opto-electronic devices. Gold is an important material for plasmonic waveguides, but although its linear optical properties are fairly well understood, the nonlinear response is still under investigation. We consider propagation of pulses in ultrathin gold strip waveguides, modeled by the nonlinear Schr\"odinger equation. The nonlinear response of gold is accounted for by the two-temperature model, revealing it as a delayed nonlinearity intrinsic in gold. The consequence is that the measured nonlinearities are strongly dependent on pulse duration. This issue has so far only been addressed phenomenologically, but we provide an accurate estimate of the quantitative connection as well as a phenomenological theory to understand the enhanced nonlinear response as the gold thickness is reduced. In comparison with the previous works, the analytical model for the power-loss equation has been improved, and can be applied now to cases with a high laser peak power. We show new fits to experimental data from literature and provide updated values for the real and imaginary part of the nonlinear susceptibility of gold for various pulse durations and gold layer thicknesses. Our simulations show that the nonlinear loss is inhibiting efficient nonlinear interaction with low-power laser pulses. We therefore propose to design waveguides suitable for the mid-IR, where the ponderomotive instantaneous nonlinearity can dominate over the delayed hot-electron nonlinearity and provide a suitable plasmonics platform for efficient ultrafast nonlinear optics.Comment: J. Opt., in pres

Subwavelength terahertz imaging with graphene hyperlens

The terahertz (THz) technology provides with striking possibilities for defense, spectroscopy and biomedical imaging [1]. However, a large wavelength (λ > 10 μm) does not allow resolving tiny details. One of the solutions is a lens consisting of a material with the hyperbolic dispersion (hyperlens) [2]. Direct scaling of optical designs to the THz range is not possible, since metal’s negative permittivity becomes too large in absolute value. This is why the employment of new materials is required.In this contribution we report for the first time the graphene wire medium based hyperlens. Stacking multiple structured graphene layers provides the hyperbolic dispersion. To restore the graphene wire medium dispersion diagrams and isofrequency contours we developed a rigorous numerical method. It also gives the possibility to calculate the permittivity tensor and to check the applicability of the homogeneous medium approach.Our numerical simulations in COMSOL and CST Microwave Studio confirm the subwavelength imaging properties of the graphene hyperlens. An example of magnification of two point sources separated by λ/5 to the size of few wavelength, which then can be detected with conventional optics, at frequency f = 6 THz (λ=50 μm) is shown in the Fig. 1. The details of the graphene hyperlens design as well as the dispersion diagram calculation method will be provided during the presentation

Nanocouplers for Infrared and Visible Light

An efficient and compact coupler—a device that matches a microwaveguide and a nanowaveguide—is an essential component for practical applications of nanophotonic systems. The number of coupling approaches has been rapidly increasing in the past ten years with the help of plasmonic structures and metamaterials. In this paper we overview recent as well as common solutions for nanocoupling. More specifically we consider the physical principles of operation of the devices based on a tapered waveguide section, a direct coupler, a lens, and a scatterer and support them with a number of examples

Wave Propagation Retrieval Method For Metamaterials: Unambiguous Restoration Of Effective Parameters

In this article we propose a new direct method of effective parameters restoration that is based on the wave propagation phenomenon. It retrieves the effective properties unambiguously, is applicable to thick metamaterial (MTM) slabs and is easy in implementation. It is validated on the case studies of fishnet, split cube in carcass, Jerusalem cross and ultrahigh refractive index MTMs. The constraints of the method are designated.Comment: 14 pages, 10 figures, submitted to Physical Review

Epsilon-Near-Zero Grids for On-chip Quantum Networks

Realization of an on-chip quantum network is a major goal in the field of integrated quantum photonics. A typical network scalable on-chip demands optical integration of single photon sources, optical circuitry and detectors for routing and processing of quantum information. Current solutions either notoriously experience considerable decoherence or suffer from extended footprint dimensions limiting their on-chip scaling. Here we propose and numerically demonstrate a robust on-chip quantum network based on an epsilon-near-zero (ENZ) material, whose dielectric function has the real part close to zero. We show that ENZ materials strongly protect quantum information against decoherence and losses during its propagation in the dense network. As an example, we model a feasible implementation of an ENZ network and demonstrate that quantum information can be reliably sent across a titanium nitride grid with a coherence length of 434 nm, operating at room temperature, which is more than 40 times larger than state-of-the-art plasmonic analogs. Our results facilitate practical realization of large multi-node quantum photonic networks and circuits on-a-chip.Comment: 13 pages, 5 figure

Homogenization of metasurfaces formed by random resonant particles in periodical lattices

In this paper we suggest a simple analytical method for description of electromagnetic properties of a geometrically regular two-dimensional subwavelength arrays (metasurfaces) formed by particles with randomly fluctuating polarizabilities. Such metasurfaces are of topical importance due to development of mass-scale bottom-up fabrication methods, for which fluctuations of the particles sizes, shapes, and/or composition are inevitable. Understanding and prediction of electromagnetic properties of such random metasurfaces is a challenge. We propose an analytical homogenization method applicable for normal wave incidence on particles arrays with dominating electric dipole responses and validate it with numerical point-dipole modeling using the supercell approach. We demonstrate that fluctuations of particles polarizabilities lead to increased diffuse scattering despite the subwavelength lattice constant of the array. The proposed method can be readily extended to oblique incidence and particles with both electric and magnetic dipole resonances.Comment: 10 pages, 5 figure

Refraction enhancement in plasmonics by the coherent control of plasmon resonances

A plasmonic nanoantenna probed by a plane-polarized optical field in a medium with no gain materials can show zero absorption or even amplification, while exhibiting maximal polarizability. This occurs through coupling to an adjacent nanoantenna in a specially designed metamolecule, which is pumped by an orthogonal optical field with phase shift. The introduced scheme is a classical counterpart of an effect known in quantum optics as enhancement of the index of refraction (EIR). In contrary to electromagnetically induced transparency (EIT), where the medium is rendered highly dispersive at the point of zero susceptibility and minimum absorption, in the EIR the system exhibits large susceptibility and low dispersion at the point of zero or negative absorption. The plasmonic analogue of the EIR allows for coherent control over the polarizability and absorption of plasmonic nanoantennas, offering a novel approach to all optical switching and coherent control of transmission, diffraction and polarization conversion properties of plasmonic nanostructures, as well as propagation properties of surface plasmon polaritons on metasurfaces. It may also open up the way for lossless or amplifying propagation of optical waves in zero-index to high refractive index plasmonic metamaterial