In this paper an on-chip device capable of wavelength-selective generation of vortex beams is demonstrated. The device is realized by integrating a spiral phase-plate onto a MEMS tunable Fabry-Perot filter. This vortex-MEMS filter, being capable of functioning simultaneously in wavelength and orbital angular momentum (OAM) domains at around 1550 nm, is considered as a compact, robust and cost-effective solution for simultaneous OAM- and WDM optical communications. Experimental spectra for azimuthal orders 1, 2 and 3 show OAM state purity >92% across 30 nm wavelength range. A demonstration of multi-channel transmission is carried out as a proof of concept.
The prediction of plasmonic laser (spaser) and its experimental realization in various systems have been among the highlights in the rapidly developing field of plasmonics during the past decade. First observed in gold nanoparticles (NP) coated by dye-doped dielectric shells spasing action was reported in hybrid plasmonic waveguides, semiconductor quantum dots on metal film, plasmonic nanocavities and nanocavity arrays, metallic NP and nanorods, and recently was studied in graphene-based structures. The small spaser size well below the diffraction limit gives rise to numerous promising applications, e.g., in sensing or medical diagnostics. However, most experimental realizations of spaser-based nanolasers were carried in relatively large systems, while only a handful of experiments reported spasing action in small systems with overall size below 50 nm. In this work, we perform a numerical study of the role of quenching and direct interactions between gain molecules in reaching the lasing threshold for small spherical NP with metal core and dye-doped dielectric shell. We use a semiclassical approach that combines Maxwell-Bloch equations with the Green function formalism to derive the threshold condition in terms of exact system eigenstates, which we find numerically. We show that for a large number of gain molecules needed to satisfy loss compensation condition, the coupling to nonresonant modes plays no significant role. In contrast, the direct dipole-dipole interactions, by causing random shifts in gain molecules' excitation energies, can hinder reaching the lasing threshold in small NP-based spasers.
We here presents the first unified theory of the response of plasmonic nanoshells assisted by optical gain media. Our approach combines rigorous Mie scattering equations for the plasmonic structure and the density matrix formalism, which is well known in laser physics, allowing a correct description of different relaxation and energy exchange channels in the system. We derive a fundamental equation for calculation of SPASER frequency which we claim to be valid for any type of SPASER physical geometry. We demonstrate that ONLY radiative losses are responsible for the spasing and loss compensation process in the laser resonator.
Properties of metamaterials are usually discussed in terms of biaxial anisotropic material parameters. To consider the
underlying constitutive relations as valid, it is required that only weak spatial dispersion occurs. At operational
frequencies of optical metamaterials this assumption often ceases to be valid. A description using effective material
properties tends to be inadequate and new approaches are required. We outline here our latest achievements along this
direction and discuss two approaches. The first one assumes that if it is not possible to introduce useful effective
properties, a more primary source of information should be used to quantify metamaterials, leading to a characterization
of metamaterials in terms of Jones matrices. We discuss the implications of this description and show that all
metamaterials can be categorized into five classes, each with distinct properties. The second approach resorts to an
effective description but restricts its considerations to a dispersion relation, characterizing the propagation of light in
bulk metamaterials, and an impedance, characterizing the coupling between metamaterials and their surroundings.
Definitions of both properties linked to a single Bloch mode are discussed and metamaterials are introduced which can
be homogenized while considering only this single mode.
The influence of the lateral asymmetry of the double-wires on the macroscopic effective parameters of the
metamaterial was investigated using the multipole model. Investigations have shown that the system dynamics
is dominated by the largest wire, which plasmonic oscillations define the orientation and the strength of the
microscopic currents in the system. As a result the magnetization of the material can be enhanced for certain
asymmetric configurations of the constitutive double-wires.
Metamaterials are composites consisting of artificial
meta-atoms/metamolecules with typical sizes less than the
wavelength of operation. One of the key properties that makes metamaterials distinctly different form the natural media is
a very strong magnetic response that can be engineered in the visible and infra-red part of the spectrum.
In this work we summarize our multipole expansion approach that can be used to describe analytically optical properties
of metamaterials composed of, in particular, the split-ring and
cut-wire resonators. An important feature of our
formalism is the possibility of describing nonlinear response of a metamaterial, such as second harmonic generation,
which arises due to induced high-order multipoles.
Our model has recently been extended to the case of hybrid metamaterials composed of plasmonic nano-resonators
coupled with quantum elements (such as quantum dots, carbon nano tubes etc). It has also been shown that apart from
metamaterials various other physical systems can be successfully modelled within framework of the developed approach.
For example, transient dynamics and steady-state regime of a
nano-laser, as well as its stochastic properties (e.g.
linewidth of generation) have been described using this model.
A simple analytical model has been developed within the scopes of the macroscopic Maxwell's equations. In the
framework of this model the dispersion relation for plane waves has been calculated for the case of Cut-Wire (CW) and
Split Ring Resonator (SRR) geometries. The dispersion relation has been compared with rigorous numerical calculations.
A possible way to introduce the electric and magnetic material parameters has been suggested. Validity criteria and
applicability limitations of the developed model are discussed. A new type of nonlinearity specific for the metamaterials
- Multipole Nonlinearity - is identified based on the developed model, wheras the second harmonic generation (SHG)
process is considered in detail
The properties of metamaterials made of an increasing number of discrete functional layers are analyzed.
Convergence of the effective properties towards their bulk counterparts is observed if the light propagation in the
metamaterial is dominated by a single eigenmode. The effective properties of the finite structure will be
compared to the properties of the infinite structure for which an effective refractive index can be derived from
the dispersion relation. The dispersion relation is furthermore shown to be useful in deriving angle dependent
effective material parameters. They are compared to the effective properties obtained from a finite slab by
applying a dedicated retrieval procedure.
An analytical description for plane wave propagation in metamaterials (MM) is presented. It follows the usual
approach for describing light propagation in homogenous media on the basis of Maxwell's equations, though
applied to a medium composed of metallic nanostructures. Here, as an example, these nanostructures are double
(or cut) wires. In the present approach the multipole expansion technique is used to account for the electric and
magnetic dipole as well as the electric quadrupole moments of the carrier distribution within the nanostructure
where a model of coupled oscillators is used for the description of the internal charge density dynamics. It is
shown how expressions for the effective permittivity and permeability can be derived from analytical
expressions for the dispersion relation, the magnetization and the electric displacement field. Results of the
analytical model are compared with rigorous simulations of Maxwell's equations yielding the limitations and
applicability of the proposed model.