We employ transformation optics to optimize the generic nonlinear wave interaction of second-harmonic generation from a pair of touching metallic wires. We demonstrate a 10 orders of magnitude increase in the second-harmonic scattering cross-section by increasing the background permittivity and a 5 orders of magnitude increase in efficiency with respect to a single wire. These results have clear implications for the design of nanostructured metallic frequency-conversion devices. Finally, we exploit our analytic solution of a non-trivial nanophotonic geometry as a platform for performing a critical comparison of the strengths, weaknesses and validity of other prevailing theoretical approaches previously employed for nonlinear wave interactions at the nanoscale.
We employ transformation optics to study analytically nonlinear wave mixing from a singular geometry of touching plasmonic wires. We obtain the analytic solution of the near-field and complement it with a solution of the far-field properties. We find, somewhat surprisingly, that optimal efficiency (in both regimes) is obtained for the degenerate case of the Second-harmonic generation. We exploit the analytic solution obtained to trace this behaviour to the spatial overlap of the input fields near the geometric singularity.
When metallic (or plasmonic) nanospheres are nearly touching, strong concentration of light can occur in the narrow gap regions. This phenomenon has a potential application in nanophotonics, biosensing and spectroscopy. The understanding of the strong interaction between the plasmonic spheres turns out to be quite challenging. Indeed, an extremely high computational cost is required to compute the electromagnetic field. Also, the classical method of image charges, which is effective for dielectric spheres system, is not valid for plasmonic spheres because of their negative permittivities. Here…
We present a theoretical study of the spontaneous emission of a line dipole source embedded in a graphene--coated subwavelength wire of arbitrary shape. The modification of the emission and the radiation efficiencies are calculated by means of a rigorous electromagnetic method based on Green's second identity. Enhancement of these efficiencies is observed when the emission frequency coincides with one of the plasmonic resonance frequencies of the wire. The relevance of the dipole emitter position and the dipole moment orientation are evaluated. We present calculations of the near--field distri…
We propose ultra-broadband reflective and absorptive polarizers in the visible range using multi-scaled Ag nano wire-slit arrays. The nano arrays can be tuned from reflective to absorptive by incorporating Ag wires/strips with different lengths/widths. The ultra-broadband nature of the absorptive array, with averaged absorption as high as ~80%, is due to the collective excitations of plasmonic resonances in the Ag wires/strips with different length scales. The Ag nano wire-slit arrays are realized experimentally by using a simple two-times shadowing vapor deposition method. They exhibit broadb…
The electromagnetic response of subwavelength wires coated with a graphene monolayer illuminated by a linearly polarized plane waves is investigated. The results show that the scattering and extintion cross-sections of the coated wire can be dramatically enhanced when the incident radiation resonantly excites localized surface plasmons. The enhancements occur for p--polarized incident waves and for excitation frequencies that correspond to complex poles in the coefficients of the multipole expansion for the scattered field. By dynamically tuning the chemical potential of graphene, the spectral…
One fundamental motivation to know the dispersive, or frequency dependent characteristics of localized surface plasmons (LSPs) supported by elliptical shaped particles wrapped with graphene sheet, as well as their scattering characteristics when these elliptical LSPs are excited, is related with the design of plasmonic structures capable to manipulate light at sub-wavelength scale. The anisotropy imposed by the ellipse eccentricity can be used as a geometrical tool for controlling plasmonic resonances. Unlike metallic case, where the multipolar eigenmodes are independent of each other, we find…
We present a rigorous electromagnetic method based on Green's second identity for studying the plasmonic response of graphene-coated wires of arbitrary shape. The wire is illuminated perpendicular to its axis by a monochromatic electromagnetic wave and the wire substrate is homogeneous and isotropic. The field is expressed everywhere in terms of two unknown source functions evaluated on the graphene coating which can be obtained from the numerical solution of a coupled pair of inhomogeneous integral equations. To assess the validity of the Green formulation, the scattering and absorption effic…
In most studies on all-optical diodes spatial asymmetry has been by necessity applied to break Lorentz reciprocity. Here we suggest a paradigm for optically induced nonreciprocity in semiconductor wires which are spatially asymmetry-free and provide a very simple and efficient platform for plasmonic devices. An azimuthal magnetic field induced by a plasmonic pump in the semiconductor wire alters the material parameters and thus results in a cross-nonlinear modulation of the plasmonic signal. Peculiarly the nonlinear wavenumber shift has opposite signs for forward and backward signals whereas K…
We investigate mode converters for Si wire to plasmonic slot waveguides at 1550 nm telecom wavelength. The structures are based on a taper geometry. We provide optimal dimensions with more than 90% power transmission for a range of metal (Au) thicknesses between 30-250 nm. We provide details on how to differentiate between the total power and the power in the main mode of the plasmonic slot waveguide. Our analysis is based on the orthogonality of modes of the slot waveguide subject to a suitable inner product definition. Our results are relevant for lowering the insertion loss and the bit erro…
We present an optical investigation of surface plasmon polaritons propagating along nanoscale Au-wires, lithographically defined on GaAs substrates. A two-axis confocal microscope was used to perform spatially and polarization resolved measurements in order to confirm the guiding of surface plasmon polaritons over lengths ranging from $5-20 μm$ along nanowires with a lateral dimension of only $\approx 100 nm$. Finite difference time domain simulations are used to corroborate our experimental observations and highlight the potential to couple proximal quantum dot emitters to propagating plasmon…
Terahertz (THz) band is considered as the next frontier in wireless communications. The emerging THz multiplexing techniques are expected to dramatically increase the information capacity of THz communications far beyond a single channel limit. In this work, we explore the THz frequency-division multiplexing modality enabled by novel add-drop multiplexer (ADM) design. Based on modular two-wire plasmonic waveguides fabricated using additive manufacturing and metallization techniques, we demonstrate four-port THz ADMs containing grating-loaded side couplers for operation at ~140 GHz carrier freq…
A novel plasmonic THz fiber featuring two metallic wires in a porous dielectric cladding is studied for resonant sensing applications. In our design, introduction of even lossless analytes into the fiber core leads to significant changes in the modal losses, which is used as a transduction mechanism.
To enable multiple functions of plasmonic nanocircuits, it is of key importance to control the propagation properties and the modal distribution of the guided optical modes such that their impedance matches to that of nearby quantum systems and desired light-matter interaction can be achieved. Here, we present efficient mode converters for manipulating guided modes on a plasmonic two-wire transmission line. The mode conversion is achieved through varying the path length, wire cross section and the surrounding index of refraction. Instead of pure optical interference, strong near-field coupling…
Purely organic materials with negative and near-zero dielectric permittivity can be easily fabricated. Here we develop a theory of nonlinear non-steady-state organic plasmonics with strong laser pulses. The bistability response of the electron-vibrational model of organic materials in the condensed phase has been demonstrated. Non-steady-state organic plasmonics enable us to obtain near-zero dielectric permittivity during a short time. We have proposed to use non-steady-state organic plasmonics for the enhancement of intersite dipolar energy-transfer interaction in the quantum dot wire that in…
An electrically tunable terahertz (THz) plasmonic device is designed and fabricated using liquid metals (eutectic gallium indium EGaIn) and shape memory alloy wires (Flexinol). The liquid metal is injected into the voids of a poly(dimethyl) siloxane (PDMS) microfluidic mold forming a periodic array of subwavelength apertures, while the wires are inserted into the elastomer below the metal plane. When a DC voltage is applied to the wires, they contract via Joule heating, reducing the aperture periodicity and blue-shifting the transmission resonances of the device. When the voltage is removed, t…
The research area of plasmonics promises devices with ultrasmall footprint operating at ultrafast speeds and with lower energy consumption compared to conventional electronics. These devices will operate with light and bridge the gap between microscale dielectric photonic systems and nanoscale electronics. Recent research advancements in nanotechnology and optics have led to the creation of a plethora of new plasmonic designs. Among the most promising are nanoscale antennas operating at optical frequencies, called nanoantennas. Plasmonic nanoantennas can provide enhanced and controllable light…
Graphene, owing to its ability to support plasmon polariton waves in the terahertz frequency range, enables the miniaturization of antennas to allow wireless communications among nanosystems. One of the main challenges in the demonstration of graphene antennas is finding suitable terahertz sources to feed the antenna. This paper estimates the performance of a graphene RF plasmonic micro-antenna fed with a photoconductive source. The terahertz source is modeled and, by means of a full-wave EM solver, the radiated power of the device is estimated with respect to material, laser illumination and …
Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nano-antenna acting like a nano-electrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonan…
We study surface second-harmonic generation (SHG) from a singular plasmonic structure consisting of touching metallic wires. We use the technique of transformation optics and relate the structure to a rather simpler geometry, a slab waveguide. This allows us to obtain an analytical solution to the problem, revealing rich physical insights. We identify various conditions that govern the SHG efficiency. Importantly, our analysis demonstrates that apart from the mode-matching condition, phase-matching condition is relevant even for this sub-wavelength structure. Furthermore, we identify a geometr…
A new concept for second-harmonic generation (SHG) in an optical nanocircuit is proposed. We demonstrate both theoretically and experimentally that the symmetry of an optical mode alone is sufficient to allow SHG even in centro-symmetric structures made of centro-symmetric material. The concept is realized using a plasmonic two-wire transmission-line (TWTL), which simultaneously supports a symmetric and an anti-symmetric mode. We first confirm the generated second-harmonics belong only to the symmetric mode of the TWTL when fundamental excited modes are either purely symmetric or anti-symmetri…
Quantum theory of surface plasmons is very important for studying the interactions between light and different metal nanostructures in nanoplasmonics. In this work, using the canonical quantization method, the SPPs on nanowires and their orbital and spin angular momentum are investigated. The results show that the SPPs on nanowire carry both orbital and spin momentum during propagation. Later, the result is applied on the plasmonic nanowire waveguide to show the agreement of the theory. The study is helpful for the nano wire based plasmonic interactions and the quantum information based optica…
We compare the optical response of isolated nanowires, double-wire systems, and Pi-structures, and show that their radiation is well described in terms of their electric and magnetic dipole moments. We also show that both dielectric permittivity and magnetic permeability can be negative at optical and near infrared frequencies, and demonstrate the connection between the geometry of the system and its resonance characteristics. We conclude that plasmonic nanowires can be employed for developing novel negative-index materials. Finally, we demonstrate that it is possible to construct a nanowire-b…
The performance of plasmonic nanoantenna structures on top of SOI wire waveguides as coherent perfect absorbers for modulators and all-optical switches is explored. The absorption, scattering, reflection and transmission spectra of gold and aluminum nanoantenna-loaded waveguides were calculated by means of 3D finite-difference time-domain simulations for single waves propagating along the waveguide, as well as for standing wave scenarios composed from two counterpropagating waves. The investigated configurations showed losses of roughly 1% and extinction ratios greater than 25 dB for modulator…
Retroreflectors that can accurately redirect the incident wave in free space back along its original channel provide unprecedented opportunities for light manipulation in wireless communication. However, to the best of our knowledge, the existing methods of designing retroreflectors suffer from either the bulky size, narrow angular bandwidth, or time-consuming post-processing. Here, a scheme of designing ultrathin and all-angle retroreflectors based on hyperbolic plasmonic metasurfaces is proposed and experimentally demonstrated. The physical mechanism underlying this scheme is the high-effici…
Spin and orbital angular momenta (AM) of light are well studied for free-space electromagnetic fields, even nonparaxial. One of the important applications of these concepts is the information transfer using AM modes, often via optical fibers and other guiding systems. However, the self-consistent description of the spin and orbital AM of light in optical media (including dispersive and metallic cases) was provided only recently [K.Y. Bliokh et al., Phys. Rev. Lett. 119, 073901 (2017)]. Here we present the first accurate calculations, both analytical and numerical, of the spin and orbital AM, a…
Plasmons in two-dimensional electron systems (2DES) feature ultra-strong confinement and are expected to efficiently mediate the interactions between light and charge carriers. Despite these expectations, the electromagnetic detectors exploiting 2d plasmon resonance have been so far inferior to their non-resonant counterparts. Here, we theoretically analyse the origin of these failures, and suggest a proper niche for 2d plasmonics in electromagnetic wave detection. We find that a confined 2DES supporting plasmon resonance has an upper limit of absorption cross-section, which is identical to th…
