8,043 research outputs found
Two mechanisms of disorder-induced localization in photonic-crystal waveguides
Unintentional but unavoidable fabrication imperfections in state-of-the-art
photonic-crystal waveguides lead to the spontaneous formation of
Anderson-localized modes thereby limiting slowlight propagation and its
potential applications. On the other hand, disorder-induced cavities offer an
approach to cavity-quantum electrodynamics and random lasing at the nanoscale.
The key statistical parameter governing the disorder effects is the
localization length, which together with the waveguide length determines the
statistical transport of light through the waveguide. In a disordered
photonic-crystal waveguide, the localization length is highly dispersive, and
therefore, by controlling the underlying lattice parameters, it is possible to
tune the localization of the mode. In the present work, we study the
localization length in a disordered photonic-crystal waveguide using numerical
simulations. We demonstrate two different localization regimes in the
dispersion diagram where the localization length is linked to the density of
states and the photon effective mass, respectively. The two different
localization regimes are identified in experiments by recording the
photoluminescence from quantum dots embedded in photonic-crystal waveguides.Comment: Accepted for publication in Physical Review
Dynamics of localization in a waveguide
This is a review of the dynamics of wave propagation through a disordered
N-mode waveguide in the localized regime. The basic quantities considered are
the Wigner-Smith and single-mode delay times, plus the time-dependent power
spectrum of a reflected pulse. The long-time dynamics is dominated by resonant
transmission over length scales much larger than the localization length. The
corresponding distribution of the Wigner-Smith delay times is the Laguerre
ensemble of random-matrix theory. In the power spectrum the resonances show up
as a 1/t^2 tail after N^2 scattering times. In the distribution of single-mode
delay times the resonances introduce a dynamic coherent backscattering effect,
that provides a way to distinguish localization from absorption.Comment: 18 pages including 8 figures; minor correction
Position-dependent diffusion of light in disordered waveguides
Diffusion has been widely used to describe a random walk of particles or
waves, and it requires only one parameter -- the diffusion constant. For waves,
however, diffusion is an approximation that disregards the possibility of
interference. Anderson localization, which manifests itself through a vanishing
diffusion coefficient in an infinite system, originates from constructive
interference of waves traveling in loop trajectories -- pairs of time-reversed
paths returning to the same point. In an open system of finite size, the return
probability through such paths is reduced, particularly near the boundary where
waves may escape. Based on this argument, the self-consistent theory of
localization and the supersymmetric field theory predict that the diffusion
coefficient varies spatially inside the system. A direct experimental
observation of this effect is a challenge because it requires monitoring wave
transport inside the system. Here, we fabricate two-dimensional photonic random
media and probe position-dependent diffusion inside the sample from the third
dimension. By varying the geometry of the system or the dissipation which also
limits the size of loop trajectories, we are able to control the
renormalization of the diffusion coefficient. This work shows the possibility
of manipulating diffusion via the interplay of localization and dissipation.Comment: 24 pages, 6 figure
Strongly coupled slow-light polaritons in one-dimensional disordered localized states
Cavity quantum electrodynamics advances the coherent control of a single
quantum emitter with a quantized radiation field mode, typically piecewise
engineered for the highest finesse and confinement in the cavity field. This
enables the possibility of strong coupling for chip-scale quantum processing,
but till now is limited to few research groups that can achieve the precision
and deterministic requirements for these polariton states. Here we observe for
the first time coherent polariton states of strong coupled single quantum dot
excitons in inherently disordered one-dimensional localized modes in slow-light
photonic crystals. Large vacuum Rabi splittings up to 311 {\mu}eV are observed,
one of the largest avoided crossings in the solid-state. Our tight-binding
models with quantum impurities detail these strong localized polaritons,
spanning different disorder strengths, complementary to model-extracted pure
dephasing and incoherent pumping rates. Such disorder-induced slow-light
polaritons provide a platform towards coherent control, collective
interactions, and quantum information processing.Comment: 17 pages, 5 figures and supplementary informatio
All-optical radiofrequency modulation of Anderson-localized modes
All-optical modulation of light relies on exploiting intrinsic material
nonlinearities. However, this optical control is rather challenging due to the
weak dependence of the refractive index and absorption coefficients on the
concentration of free carriers in standard semiconductors. To overcome this
limitation, resonant structures with high spatial and spectral confinement are
carefully designed to enhance the stored electromagnetic energy, thereby
requiring lower excitation power to achieve significant nonlinear effects.
Small mode-volume and high quality (Q)-factor cavities also offer an efficient
coherent control of the light field and the targeted optical properties. Here,
we report on optical resonances reaching Q - 10^5 induced by disorder on novel
photonic/phononic crystal waveguides. At relatively low excitation powers
(below 1 mW), these cavities exhibit nonlinear effects leading to periodic (up
to - 35 MHz) oscillations of their resonant wavelength. Our system represents a
test-bed to study the interplay between structural complexity and material
nonlinearities and their impact on localization phenomena and introduces a
novel functionality to the toolset of disordered photonics
Polaritonic states in a dielectric nanoguide: localization and strong coupling
Propagation of light through dielectrics lies at the heart of optics.
However, this ubiquitous process is commonly described using phenomenological
dielectric function and magnetic permeability , i.e. without
addressing the quantum graininess of the dielectric matter. Here, we present a
theoretical study where we consider a one-dimensional ensemble of atoms in a
subwavelength waveguide (nanoguide) as fundamental building blocks of a model
dielectric. By exploring the roles of the atom-waveguide coupling efficiency,
density, disorder, and dephasing, we establish connections among various
features of polaritonic light-matter states such as localization, super and
subradiance, and strong coupling. In particular, we show that coherent multiple
scattering of light among atoms that are coupled via a single propagating mode
can gives rise to Rabi splitting. These results provide important insight into
the underlying physics of strong coupling reported by recent room-temperature
experiments with microcavities and surface plasmons.Comment: 10 pages, 6 figure
Photon scattering by a three-level emitter in a one-dimensional waveguide
We discuss the scattering of photons from a three-level emitter in a
one-dimensional waveguide, where the transport is governed by the interference
of spontaneously emitted and directly transmitted waves. The scattering problem
is solved in closed form for different level structures. Several possible
applications are discussed: The state of the emitter can be switched
deterministically by Raman scattering, thus enabling applications in quantum
computing such as a single photon transistor. An array of emitters gives rise
to a photonic band gap structure, which can be tuned by a classical driving
laser. A disordered array leads to Anderson localization of photons, where the
localization length can again be controlled by an external driving.Comment: 17 pages, 8 figure
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