239 research outputs found
Directive emission of red conjugated polymer embedded within zero index metamaterials
Abstract: We numerically demonstrate an impedance-matched multilayer stacked fishnet metamaterial that has zero index with flat high transmittance from 600nm to 620nm. The effective refractive index
Microwave properties of an inhomogeneous optically illuminated plasma in a microstrip gap
The optical illumination of a microstrip gap on a thick semiconductor substrate creates an inhomogeneous electron-hole plasma in the gap region. This allows the study of the propagation mechanism through the plasma region. This paper uses a multilayer plasma model to explain the origin of high losses in such structures. Measured results are shown up to 50 GHz and show good agreement with the simulated multilayer model. The model also allows the estimation of certain key parameters of the plasma, such as carrier density and diffusion length, which are difficult to measure by direct means. The detailed model validation performed here will enable the design of more complex microwave structures based on this architecture. While this paper focuses on monocrystalline silicon as the substrate, the model is easily adaptable to other semiconductor materials such as GaAs
GaN directional couplers for integrated quantum photonics
Large cross-section GaN waveguides are proposed as a suitable architecture to
achieve integrated quantum photonic circuits. Directional couplers with this
geometry have been designed with aid of the beam propagation method and
fabricated using inductively coupled plasma etching. Scanning electron
microscopy inspection shows high quality facets for end coupling and a well
defined gap between rib pairs in the coupling region. Optical characterization
at 800 nm shows single-mode operation and coupling-length-dependent splitting
ratios. Two photon interference of degenerate photon pairs has been observed in
the directional coupler by measurement of the Hong-Ou-Mandel dip with 96%
visibility.Comment: 4 pages, 5 figure
Fast Tuning of Double Fano Resonance Using A Phase-Change Metamaterial Under Low Power Intensity
In this work, we numerically demonstrate an all-optical tunable Fano resonance in a fishnet metamaterial(MM) based on a metal/phase-change material(PCM)/metal multilayer. We show that the displacement of the elliptical nanoholes from their centers can split the single Fano resonance (FR) into a double FR, exhibiting higher quality factors. The tri-layer fishnet MMs with broken symmetry accomplishes a wide tuning range in the mid-infrared(M-IR) regime by switching between the amorphous and crystalline states of the PCM (Ge(2)Sb(2)Te(5)). A photothermal model is used to study the temporal variation of the temperature of the Ge(2)Sb(2)Te(5) film to show the potential for switching the phase of Ge(2)Sb(2)Te(5) by optical heating. Generation of the tunable double FR in this asymmetric structure presents clear advantages as it possesses a fast tuning time of 0.36 ns, a low pump light intensity of 9.6 μW/μm(2), and a large tunable wavelength range between 2124 nm and 3028 nm. The optically fast tuning of double FRs using phase change metamaterials(PCMMs) may have potential applications in active multiple-wavelength nanodevices in the M-IR region
Transfer of arbitrary quantum emitter states to near-field photon superpositions in nanocavities
We present a method to analyze the suitability of particular photonic cavity
designs for information exchange between arbitrary superposition states of a
quantum emitter and the near-field photonic cavity mode. As an illustrative
example, we consider whether quantum dot emitters embedded in "L3" and "H1"
photonic crystal cavities are able to transfer a spin superposition state to a
confined photonic superposition state for use in quantum information transfer.
Using an established dyadic Green's function (DGF) analysis, we describe
methods to calculate coupling to arbitrary quantum emitter positions and
orientations using the modified local density of states (LDOS) calculated using
numerical finite-difference time-domain (FDTD) simulations. We find that while
superposition states are not supported in L3 cavities, the double degeneracy of
the H1 cavities supports superposition states of the two orthogonal modes that
may be described as states on a Poincar\'{e}-like sphere. Methods are developed
to comprehensively analyze the confined superposition state generated from an
arbitrary emitter position and emitter dipole orientation.Comment: 22 pages, 9 figure
Broadband polarization-independent perfect absorber using a phase-change metamaterial at visible frequencies
We report a broadband polarization-independent perfect absorber with wide-angle near unity absorbance in the visible regime. Our structure is composed of an array of thin Au squares separated from a continuous Au film by a phase change material (Ge(2)Sb(2)Te(5)) layer. It shows that the near perfect absorbance is flat and broad over a wide-angle incidence up to 80° for either transverse electric or magnetic polarization due to a high imaginary part of the dielectric permittivity of Ge(2)Sb(2)Te(5). The electric field, magnetic field and current distributions in the absorber are investigated to explain the physical origin of the absorbance. Moreover, we carried out numerical simulations to investigate the temporal variation of temperature in the Ge(2)Sb(2)Te(5) layer and to show that the temperature of amorphous Ge(2)Sb(2)Te(5) can be raised from room temperature to > 433 K (amorphous-to-crystalline phase transition temperature) in just 0.37 ns with a low light intensity of 95 nW/μm(2), owing to the enhanced broadband light absorbance through strong plasmonic resonances in the absorber. The proposed phase-change metamaterial provides a simple way to realize a broadband perfect absorber in the visible and near-infrared (NIR) regions and is important for a number of applications including thermally controlled photonic devices, solar energy conversion and optical data storage
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