45 research outputs found
Theoretical and computational analysis of second- and third-harmonic generation in periodically patterned graphene and transition-metal dichalcogenide monolayers
Remarkable optical and electrical properties of two-dimensional (2D)
materials, such as graphene and transition-metal dichalcogenide (TMDC)
monolayers, offer vast technological potential for novel and improved
optoelectronic nanodevices, many of which relying on nonlinear optical effects
in these 2D materials. This article introduces a highly effective numerical
method for efficient and accurate description of linear and nonlinear optical
effects in nanostructured 2D materials embedded in periodic photonic structures
containing regular three-dimensional (3D) optical materials, such as
diffraction gratings and periodic metamaterials. The proposed method builds
upon the rigorous coupled-wave analysis and incorporates the nonlinear optical
response of 2D materials by means of modified electromagnetic boundary
conditions. This allows one to reduce the mathematical framework of the
numerical method to an inhomogeneous scattering matrix formalism, which makes
it more accurate and efficient than previously used approaches. An overview of
linear and nonlinear optical properties of graphene and TMDC monolayers is
given and the various features of the corresponding optical spectra are
explored numerically and discussed. To illustrate the versatility of our
numerical method, we use it to investigate the linear and nonlinear
multiresonant optical response of 2D-3D heteromaterials for enhanced and
tunable second- and third-harmonic generation. In particular, by employing a
structured 2D material optically coupled to a patterned slab waveguide, we
study the interplay between geometric resonances associated to guiding modes of
periodically patterned slab waveguides and plasmon or exciton resonances of 2D
materials.Comment: 28 pages, 21 figure
Optically controllable coupling between edge and topological interface modes of graphene metasurfaces
Nonlinear topological photonics has been attracting increasing research interest, as it provides an exciting photonic platform that combines the advantages of active all-opticall control offered by nonlinear optics with the unique features of topological photonic systems, such as topologically-protected defect-immune light propagation. In this paper, we demonstrate that topological interface modes and trivial edge modes of a specially designed graphene metasurface can be coupled in a tunable and optically controllable manner, thus providing an efficient approach to transfer optical power to topologically protected states. This is achieved in a pump-signal configuration, in which an optical pump propagating in a bulk mode of the metasurface is employed to tune the band structure of the photonic system and, consequently, the coupling coefficient and wave-vector mismatch between edge and topological interface modes. This tunable coupling mechanism is particularly efficient due to the large Kerr coefficient of graphene. Importantly, we demonstrate that the required pump power can be significantly reduced if the optical device is operated in the slow-light regime. We performed our analysis using both \textit{ab initio} full-wave simulations and a coupled-mode theory that captures the main physics of this active coupler and observe a good agreement between the two approaches. This work may lead to the design of active topological photonic devices with new or improved functionality
Accurate near-field calculation in the rigorous coupled-wave analysis method
The rigorous coupled-wave analysis (RCWA) is one of the most successful and
widely used methods for modeling periodic optical structures. It yields fast
convergence of the electromagnetic far-field and has been adapted to model
various optical devices and wave configurations. In this article, we
investigate the accuracy with which the electromagnetic near-field can be
calculated by using RCWA and explain the observed slow convergence and
numerical artifacts from which it suffers, namely unphysical oscillations at
material boundaries due to the Gibb's phenomenon. In order to alleviate these
shortcomings, we also introduce a mathematical formulation for accurate
near-field calculation in RCWA, for one- and two-dimensional straight and
slanted diffraction gratings. This accurate near-field computational approach
is tested and evaluated for several representative test-structures and
configurations in order to illustrate the advantages provided by the proposed
modified formulation of the RCWA.Comment: 13 pages, 12 figure
Nonlinear optics in diamond-fin photonic nanowires: soliton formation and frequency comb generation
We present a detailed study of the nonlinear optical properties of newly developed subwavelength diamond-fin waveguides, along with an analysis of soliton generation and pulse spectral broadening in these structures. Our rigorous mathematical model includes all the key linear and nonlinear optical effects that govern the pulse dynamics in these diamond waveguides. As a relevant application of our investigations, we demonstrate how these waveguides can be employed to efficiently generate frequency combs in the visible spectral domain
Optically and Electrically Tunable Dirac Points and Zitterbewegung in Graphene-Based Photonic Superlattices
We demonstrate that graphene-based photonic superlattices provide a versatile
platform for electrical and all-optical control of photonic beams with
deep-subwavelength accuracy. Specifically, by inserting graphene sheets into
periodic metallo-dielectric structures one can design optical superlattices
that posses photonic Dirac points (DPs) at frequencies at which the spatial
average of the permittivity of the superlattice, ,
vanishes. Similar to the well-known zero- bandgaps, we show that these
zero- DPs are highly robust against structural disorder. We
also show that, by tuning the graphene permittivity via the optical Kerr effect
or electrical doping, one can induce a spectral variation of the DP exceeding
\SI{30}{\nano\meter}, at mid-IR and THz frequencies. The implications of this
wide tunability for the photonic Zitterbewegung effect in a vicinity of the DP
are explored too.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B as a Rapid
Communicatio