645 research outputs found
Room temperature plasmon laser by total internal reflection
Plasmon lasers create and sustain intense and coherent optical fields below
light's diffraction limit with the unique ability to drastically enhance
light-matter interactions bringing fundamentally new capabilities to
bio-sensing, data storage, photolithography and optical communications.
However, these important applications require room temperature operation, which
remains a major hurdle. Here, we report a room temperature semiconductor
plasmon laser with both strong cavity feedback and optical confinement to
1/20th of the wavelength. The strong feedback arises from total internal
reflection of surface plasmons, while the confinement enhances the spontaneous
emission rate by up to 20 times.Comment: 8 Page, 2 Figure
Nanofocusing in SOI-based hybrid plasmonic metal slot waveguides
Abstract: Through a process of efficient dielectric to metallic waveguide mode conversion, we calculate a >400-fold field intensity enhancement in a silicon photonics compatible nanofocusing device. A metallic slot waveguide sits on top of the silicon slab waveguide with nanofocusing being achieved by tapering the slot width gradually. We evaluate the conversion between the numerous photonic modes of the planar silicon waveguide slab and the most confined plasmonic mode of a 20 x 50 nm2 slot in the metallic film. With an efficiency of ~80%, this system enables remarkably effective nanofocusing, although the small amount of inter-mode coupling shows that this structure is not quite adiabatic. In order to couple photonic and plasmonic modes efficiently, in-plane focusing is required, simulated here by curved input grating couplers. The nanofocusing device shows how to efficiently bridge the photonic micro-regime and the plasmonic nano-regime whilst maintaining compatibility with the silicon photonics platform
Anomalous Stark Shifts in Single Vertically Coupled Pairs of InGaAs Quantum Dots
Vertically coupled Stranski Krastanow QDs are predicted to exhibit strong
tunnelling interactions that lead to the formation of hybridised states. We
report the results of investigations into single pairs of coupled QDs in the
presence of an electric field that is able to bring individual carrier levels
into resonance and to investigate the Stark shift properties of the excitons
present. Pronounced changes in the Stark shift behaviour of exciton features
are identified and attributed to the significant redistribution of the carrier
wavefunctions as resonance between two QDs is achieved. At low electric fields
coherent tunnelling between the two QD ground states is identified from the
change in sign of the permanent dipole moment and dramatic increase of the
electron polarisability, and at higher electric fields a distortion of the
Stark shift is attributed to a coherent tunnelling effect between the ground
state of the upper QD and the excited state of the lower QD.Comment: Conference paper for QD2004 3 figure
Ultrafast sub-30 FS all-optical switching based on gallium phosphide
Gallium Phosphide (GaP) is one of the few available materials with strong optical nonlinearity and negligible losses in the visible ( >450 )and near-infrared regime. In this work, we demonstrate that a GaP film can generate sub-30 fs (full width at half maximum) transmission modulation of up to ⁓70% in the 600-1000 nm wavelength range. Nonlinear simulations using parameters measured by the Z-scan approach indicate that the transmission modulation arises from the optical Kerr effect and two-photon absorption. Due to the absence of linear absorption, no slower free-carrier contribution is detected. These findings place GaP as a promising ultrafast material for all-optical switching at modulation speeds of up to 20 THz
Conditional phase shift from a quantum dot in a pillar microcavity
Large conditional phase shifts from coupled atom-cavity systems are a key
requirement for building a spin photon interface. This in turn would allow the
realisation of hybrid quantum information schemes using spin and photonic
qubits. Here we perform high resolution reflection spectroscopy of a quantum
dot resonantly coupled to a pillar microcavity. We show both the change in
reflectivity as the quantum dot is tuned through the cavity resonance, and
measure the conditional phase shift induced by the quantum dot using an ultra
stable interferometer. These techniques could be extended to the study of
charged quantum dots, where it would be possible to realise a spin photon
interface
Optical control of spin coherence in singly charged (In,Ga)As/GaAs quantum dots
Electron spin coherence has been generated optically in n-type modulation
doped (In,Ga)As/GaAs quantum dots (QDs) which contain on average a single
electron per dot. The coherence arises from resonant excitation of the QDs by
circularly-polarized laser pulses, creating a coherent superposition of an
electron and a trion state. Time dependent Faraday rotation is used to probe
the spin precession of the optically oriented electrons about a transverse
magnetic field. Spin coherence generation can be controlled by pulse intensity,
being most efficient for (2n+1)pi-pulses.Comment: 5 pages, 4 figure
Tailored quantum dots for entangled photon pair creation
We compare the asymmetry-induced exchange splitting delta_1 of the
bright-exciton ground-state doublet in self-assembled (In,Ga)As/GaAs quantum
dots, determined by Faraday rotation, with its homogeneous linewidth gamma,
obtained from the radiative decay in time-resolved photoluminescence.
Post-growth thermal annealing of the dot structures leads to a considerable
increase of the homogeneous linewidth, while a strong reduction of the exchange
splitting is simultaneously observed. The annealing can be tailored such that
delta_1 and gamma become comparable, whereupon the carriers are still well
confined. This opens the possibility to observe polarization entangled photon
pairs through the biexciton decay cascade.Comment: 4 pages, 4 figure
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