110 research outputs found
Compositional modulation in AlxGa1−xAs epilayers grown by molecular beam epitaxy on the (111) facets of grooves in a nonplanar substrate
We report the first observation of a lateral junction formed in an alloy due to an abrupt transition from segregated to random AlGaAs alloy compositions. Al0.25Ga0.75As epilayers were grown by molecular beam epitaxy on [011-bar] oriented grooves in a nonplanar (100) GaAs substrate. A quasi-periodic modulation of the aluminum concentration occurs spontaneously in material grown on the (111) facets of the groove, with a period of 50–70 Å along the [111] direction. The compositional modulation is associated with a reduction of the band gap by 130 meV, with respect to the random alloy. While segregation of the AlGaAs alloy has been seen previously, this is the first observation of segregation of AlGaAs grown on a (111) surface. The compositional modulation terminates abruptly at the boundaries of the (111) facet, forming abrupt lateral junctions in the AlGaAs layers grown on a groove
Cathodoluminescence measurement of an orientation dependent aluminum concentration in AlxGa1−xAs epilayers grown by molecular beam epitaxy on a nonplanar substrate
Cathodoluminescence scanning electron microscopy is used to study AlxGa1−x As epilayers grown on a nonplanar substrate by molecular beam epitaxy. Grooves parallel to the [011-bar] direction were etched in an undoped GaAs substrate. Growth on such grooves proceeds on particular facet planes. We find that the aluminum concentration in the epilayers is dependent on the facet orientation, changing by as much as 35% from the value in the unpatterned areas. The transition in the aluminum concentration at a boundary between two facets is observed to be very abrupt
Fast Purcell-enhanced single photon source in 1,550-nm telecom band from a resonant quantum dot-cavity coupling
High-bit-rate nanocavity-based single photon sources in the 1,550-nm telecom
band are challenges facing the development of fibre-based long-haul quantum
communication networks. Here we report a very fast single photon source in the
1,550-nm telecom band, which is achieved by a large Purcell enhancement that
results from the coupling of a single InAs quantum dot and an InP photonic
crystal nanocavity. At a resonance, the spontaneous emission rate was enhanced
by a factor of 5 resulting a record fast emission lifetime of 0.2 ns at 1,550
nm. We also demonstrate that this emission exhibits an enhanced anti-bunching
dip. This is the first realization of nanocavity-enhanced single photon
emitters in the 1,550-nm telecom band. This coupled quantum dot cavity system
in the telecom band thus provides a bright high-bit-rate non-classical single
photon source that offers appealing novel opportunities for the development of
a long-haul quantum telecommunication system via optical fibres.Comment: 16 pages, 4 figure
Vertical-external-cavity surface-emitting lasers and quantum dot lasers
The use of cavity to manipulate photon emission of quantum dots (QDs) has
been opening unprecedented opportunities for realizing quantum functional
nanophotonic devices and also quantum information devices. In particular, in
the field of semiconductor lasers, QDs were introduced as a superior
alternative to quantum wells to suppress the temperature dependence of the
threshold current in vertical-external-cavity surface-emitting lasers
(VECSELs). In this work, a review of properties and development of
semiconductor VECSEL devices and QD laser devices is given. Based on the
features of VECSEL devices, the main emphasis is put on the recent development
of technological approach on semiconductor QD VECSELs. Then, from the viewpoint
of both single QD nanolaser and cavity quantum electrodynamics (QED), a
single-QD-cavity system resulting from the strong coupling of QD cavity is
presented. A difference of this review from the other existing works on
semiconductor VECSEL devices is that we will cover both the fundamental aspects
and technological approaches of QD VECSEL devices. And lastly, the presented
review here has provided a deep insight into useful guideline for the
development of QD VECSEL technology and future quantum functional nanophotonic
devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with
arXiv:0904.369
Plasmofluidic Disk Resonators
Waveguide-coupled silicon ring or disk resonators have been used for optical signal processing and sensing. Large-scale integration of optical devices demands continuous reduction in their footprints, and ultimately they need to be replaced by silicon-based plasmonic resonators. However, few waveguide-coupled silicon-based plasmonic resonators have been realized until now. Moreover, fluid cannot interact effectively with them since their resonance modes are strongly confined in solid regions. To solve this problem, this paper reports realized plasmofluidic disk resonators (PDRs). The PDR consists of a submicrometer radius silicon disk and metal laterally surrounding the disk with a 30-nm-wide channel in between. The channel is filled with fluid, and the resonance mode of the PDR is strongly confined in the fluid. The PDR coupled to a metal-insulator-silicon-insulator-metal waveguide is implemented by using standard complementary metal oxide semiconductor technology. If the refractive index of the fluid increases by 0.141, the transmission spectrum of the waveguide coupled to the PDR of radius 0.9 mu m red-shifts by 30 nm. The PDR can be used as a refractive index sensor requiring a very small amount of analyte. Plus, the PDR filled with liquid crystal may be an ultracompact intensity modulator which is effectively controlled by small driving voltageopen
Observation of the exceptional-point-enhanced Sagnac effect
Exceptional points (EPs) are special spectral degeneracies of non-Hermitian Hamiltonians that govern the dynamics of open systems. At an EP, two or more eigenvalues, and the corresponding eigenstates, coalesce. Recently, it was predicted that operation of an optical gyroscope near an EP results in improved response to rotations. However, the performance of such a system has not been examined experimentally. Here we introduce a precisely controllable physical system for the study of non-Hermitian physics and nonlinear optics in high-quality-factor microresonators. Because this system dissipatively couples counter-propagating lightwaves within the resonator, it also functions as a sensitive gyroscope for the measurement of rotations. We use our system to investigate the predicted EP-enhanced Sagnac effect and observe a four-fold increase in the Sagnac scale factor by directly measuring rotations applied to the resonator. The level of enhancement can be controlled by adjusting the system bias relative to the EP, and modelling results confirm the observed enhancement. Moreover, we characterize the sensitivity of the gyroscope near the EP. Besides verifying EP physics, this work is important for the understanding of optical gyroscopes
Optomechanical Crystals
Structured, periodic optical materials can be used to form photonic crystals
capable of dispersing, routing, and trapping light. A similar phenomena in
periodic elastic structures can be used to manipulate mechanical vibrations.
Here we present the design and experimental realization of strongly coupled
optical and mechanical modes in a planar, periodic nanostructure on a silicon
chip. 200-Terahertz photons are co-localized with mechanical modes of Gigahertz
frequency and 100-femtogram mass. The effective coupling length, which
describes the strength of the photon-phonon interaction, is as small as 2.9
microns, which, together with minute oscillator mass, allows all-optical
actuation and transduction of nanomechanical motion with near quantum-limited
sensitivity. Optomechanical crystals have many potential applications, from
RF-over-optical communication to the study of quantum effects in mesoscopic
mechanical systems.Comment: 16 pages, 7 figure
Photonic molecules and spectral engineering
This chapter reviews the fundamental optical properties and applications of
pho-tonic molecules (PMs) - photonic structures formed by electromagnetic
coupling of two or more optical microcavities (photonic atoms). Controllable
interaction between light and matter in photonic atoms can be further modified
and en-hanced by the manipulation of their mutual coupling. Mechanical and
optical tunability of PMs not only adds new functionalities to
microcavity-based optical components but also paves the way for their use as
testbeds for the exploration of novel physical regimes in atomic physics and
quantum optics. Theoretical studies carried on for over a decade yielded novel
PM designs that make possible lowering thresholds of semiconductor microlasers,
producing directional light emission, achieving optically-induced transparency,
and enhancing sensitivity of microcavity-based bio-, stress- and
rotation-sensors. Recent advances in material science and nano-fabrication
techniques make possible the realization of optimally-tuned PMs for cavity
quantum electrodynamic experiments, classical and quantum information
processing, and sensing.Comment: A review book chapter: 29 pages, 19 figure
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