78 research outputs found
Localización anómala de la luz en superredes fotónicas unidimensionales desordenadas
The Anderson localization of light in one-dimensional disordered photonic superlattices is theoretically studied. The system is considered to be made of alternating dispersive and nondispersive layers of different randomthickness. Dispersive slabs of the heterostructure are characterized by Drude-like frequency-dependent electric permittivities and magnetic permeabilities. Numerical results for the localization length are obtained via an analytical model, only valid in the case of weak disorder, and also through its general definition involving the transmissivity of the multilayered system. Anomalous λ4- and λ-4-dependencies of the localization length in positive-negative disordered photonic superlattices are obtained, in certain cases, in the long and short wavelength limits, respectively.La localización de Anderson de la luz en superredes fotónicas desordenadas unidimensionales se estudia teóricamente. Se considera que el sistema está compuesto por capas alternas dispersivas y no dispersivas de diferente grosor aleatorio. Las losas dispersivas de la heteroestructura se caracterizan por permittividades eléctricas y permeabilidades magnéticas dependientes de la frecuencia tipo Drude. Los resultados numéricos para la longitud de localización se obtienen a través de un modelo analítico, solo válido en el caso de un trastorno débil, y también a través de su definición general que involucra la transmisividad del sistema multicapa. Se obtienen dependencias anómalas λ4 y λ-4 de la longitud de localización en superredes fotónicas desordenadas positivas-negativas, en ciertos casos, en los límites de longitud de onda larga y corta, respectivamente
Effect of hole-shape irregularities on photonic crystal waveguides
The effect of irregular hole shape on the spectrum and radiation losses of a
photonic crystal waveguide is studied using Bloch-mode expansion. Deviations
from a perfectly circular hole are characterized by a radius fluctuation
amplitude and correlation angle. It is found that the parameter which
determines the magnitude of the effect of disorder is the standard deviation of
the hole areas. Hence, for a fixed amplitude of the radius fluctuation around
the hole, those effects are strongly dependent on the correlation angle of the
irregular shape. This result suggests routes to potentially improve the quality
of photonic crystal structures.Comment: 3 pages, 3 figure
Cavity Quantum Electrodynamics with Anderson-localized Modes
A major challenge in quantum optics and quantum information technology is to
enhance the interaction between single photons and single quantum emitters.
Highly engineered optical cavities are generally implemented requiring
nanoscale fabrication precision. We demonstrate a fundamentally different
approach in which disorder is used as a resource rather than a nuisance. We
generate strongly confined Anderson-localized cavity modes by deliberately
adding disorder to photonic crystal waveguides. The emission rate of a
semiconductor quantum dot embedded in the waveguide is enhanced by a factor of
15 on resonance with the Anderson-localized mode and 94 % of the emitted
single-photons couple to the mode. Disordered photonic media thus provide an
efficient platform for quantum electrodynamics offering an approach to
inherently disorder-robust quantum information devices
Experimental observation of strong photon localization in disordered photonic crystal waveguides
We demonstrate experimentally that structural perturbations imposed on
highly-dispersive photonic crystal-based waveguides give rise to spectral
features that bear signatures of Anderson localization. Sharp resonances with
the effective Qs of over 30,000 are found in scattering spectra of disordered
waveguides. The resonances are observed in a ~20-nm bandwidth centered at the
cutoff of slowly-guided Bloch-modes. Their origin can be explained with
interference of coherently scattered electromagnetic waves which results in the
formation of a narrow impurity (or localization) band populated with spectrally
distinct quasistates. Standard photon localization criteria are fulfilled in
the localization band.Comment: first submitted to PRL on April 20th, 2007; 16 pages, 4 figure
Synchronous imaging for rapid visualization of complex vibration profiles in electromechanical microresonators
Synchronous imaging is used in dynamic space-domain vibration profile studies
of capacitively driven, thin n+ doped poly-silicon microbridges oscillating at
rf frequencies. Fast and high-resolution actuation profile measurements of
micromachined resonators are useful when significant device nonlinearities are
present. For example, bridges under compressive stress near the critical Euler
value often reveal complex dynamics stemming from a state close to the onset of
buckling. This leads to enhanced sensitivity of the vibration modes to external
conditions, such as pressure, temperatures, and chemical composition, the
global behavior of which is conveniently evaluated using synchronous imaging
combined with spectral measurements. We performed an experimental study of the
effects of high drive amplitude and ambient pressure on the resonant vibration
profiles in electrically-driven microbridges near critical buckling. Numerical
analysis of electrostatically driven post-buckled microbridges supports the
richness of complex vibration dynamics that are possible in such
micro-electromechanical devices.Comment: 7 pages, 8 figure, submitted to Physical Review
Transmission properties of a single metallic slit: From the subwavelength regime to the geometrical-optics limit
In this work we explore the transmission properties of a single slit in a
metallic screen. We analyze the dependence of these properties on both slit
width and angle of incident radiation. We study in detail the crossover between
the subwavelength regime and the geometrical-optics limit. In the subwavelength
regime, resonant transmission linked to the excitation of waveguide resonances
is analyzed. Linewidth of these resonances and their associated electric field
intensities are controlled by just the width of the slit. More complex
transmission spectra appear when the wavelength of light is comparable to the
slit width. Rapid oscillations associated to the emergence of different
propagating modes inside the slit are the main features appearing in this
regime.Comment: Accepted for publication in Phys. Rev.
Non-trivial scaling of self-phase modulation and three-photon absorption in III-V photonic crystal waveguides
We investigate the nonlinear response of photonic crystal waveguides with
suppressed two-photon absorption. A moderate decrease of the group velocity (~
c/6 to c/15, a factor of 2.5) results in a dramatic (30x) enhancement of
three-photon absorption well beyond the expected scaling, proportional to
1/(vg)^3. This non-trivial scaling of the effective nonlinear coefficients
results from pulse compression, which further enhances the optical field beyond
that of purely slow-group velocity interactions. These observations are enabled
in mm-long slow-light photonic crystal waveguides owing to the strong anomalous
group-velocity dispersion and positive chirp. Our numerical physical model
matches measurements remarkably.Comment: 10 pages, 4 figure
Lyapunov exponent of the random Schr\"{o}dinger operator with short-range correlated noise potential
We study the influence of disorder on propagation of waves in one-dimensional
structures. Transmission properties of the process governed by the
Schr\"{o}dinger equation with the white noise potential can be expressed
through the Lyapunov exponent which we determine explicitly as a
function of the noise intensity \sigma and the frequency \omega. We find
uniform two-parameter asymptotic expressions for which allow us to
evaluate for different relations between \sigma and \omega. The value
of the Lyapunov exponent is also obtained in the case of a short-range
correlated noise, which is shown to be less than its white noise counterpart.Comment: 20 pages, 4 figure
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