Temperature dependent polariton emission from strongly coupled organic semiconductor microcavities

We investigated the absorption and photoluminescence (PL) of J-aggregates of a cyanine dye both in a thin film format and when used as the active layer in a strongly-coupled microcavity. We show that as temperature is reduced, the absorption linewidth of the J-aggregates narrows and shifts to higher energy. When the J-aggregate is placed in a microcavity we find that the energy of the polariton modes also shifts to higher energies as temperature is reduced. We compare the intensity of PL emission from the upper and lower branches at resonance as a function of temperature, and find that it can be described by an activation energy of 25 meV. PL emission spectra at resonance also suggest that uncoupled excitons inside the microcavity populate the upper polariton branch states

High-occupancy effects and stimulation phenomena in semiconductor microcavities

This paper describes recent work on high-occupancy effects in semiconductor microcavities, with emphasis on the variety of new physics and the potential for applications that has been demonstrated recently. It is shown that the ability to manipulate both exciton and photon properties, and how they interact together to form strongly coupled exciton-photon coupled modes, exciton polaritons, leads to a number of very interesting phenomena, which are either difficult or impossible to achieve in bulk semiconductors or quantum wells. The very low polariton density of states enables state occupancies greater than one to be easily achieved, and hence stimulation phenomena to be realized under conditions of resonant excitation. The particular form of the lower polariton dispersion curve in microcavities allows energy and momentum conserving polariton-polariton scattering under resonant excitation. Stimulated scattering of the bosonic quasi-particles occurs to the emitting state at the center of the Brillouin zone, and to a companion state at high wave vector. The stimulation phenomena lead to the formation of highly occupied states with macroscopic coherence in two specific regions of k space. The results are contrasted with phenomena that occur under conditions of nonresonant excitation. Prospects to achieve "polariton lasing" under nonresonant excitation, and high-gain, room-temperature ultrafast amplifiers and low-threshold optical parametric oscillator under resonant excitation conditions are discussed

Beating of exciton-dressed states in a single semiconductor InGaAs/GaAs quantum dot

We report picosecond control of excitonic dressed states in a single semiconductor quantum dot. A strong laser pulse couples the exciton and biexciton states, to form an Autler-Townes doublet of the neutral exciton transition. The Rabi-splitting, and hence the admixture of the dressed states follows the envelope of the picosecond control laser. We create a superposition of dressed states, and observe the resulting beat: a direct measurement of a Rabi oscillation in time delay rather than the usual power domain

Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities

We demonstrate semiconductor quantum dots coupled to photonic crystal cavity modes operating in the visible spectrum. We present the design, fabrication, and characterization of two dimensional photonic crystal cavities in GaInP and measure quality factors in excess of 7500 at 680 nm. We demonstrate full control over the spontaneous emission rate of InP quantum dots and by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode we observe a Purcell enhancement of similar to 8. (C) 2010 American Institute of Physics. [doi:10.1063/1.3510469

Improved Temperature Performance of 1.31-mu/m Quantum Dot Lasers by Optimized Ridge Waveguide Design

In this letter, we demonstrate the importance of the fabricated device structure for the external differential efficiency, threshold current density, and maximum operating temperature for ground state operation of a 1.31-mu/m quantum dot laser. The introduction of a shallow ridge etch design and selective electroplating of the gold bondpads is demonstrated to offer improved performance in comparison to a deep ridge etch design with thinner evaporated gold bondpads

Photonic band-structure effects in the reflectivity of periodically patterned waveguides

We report sharp resonant features in the reflectivity spectra of semiconductor waveguides patterned with periodic lattices of deep holes. The resonances arise from coupling of incident light to the photonic bands of the lattice. By varying the reflection geometry, large parts of the photonic band structure are determined. A scattering matrix treatment is used to obtain theoretical spectra which agree well with experiment. The waveguide is shown to have an important influence on the band structure, including marked polarization mixing and significant energy up-shifts

High-performance three-layer 1.3-/spl mu/m InAs-GaAs quantum-dot lasers with very low continuous-wave room-temperature threshold currents

The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR)-coated facets has been utilized to obtain low threshold currents and threshold current densities for 1.3-/spl mu/m multilayer InAs-GaAs quantum-dot lasers. A very low continuous-wave (CW) room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm/sup 2/ are achieved for a three-layer device with a 1-mm HR/HR cavity. For a 2-mm cavity, the CW threshold current density is as low as 17 A/cm/sup 2/ for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets

Full Stark control of polariton states on a spin-orbit hypersphere

The orbital angular momentum and the polarization of light are physical quantities widely investigated for classical and quantum information processing. In this work we propose to take advantage of strong light-matter coupling, circular-symmetric confinement, and transverse-electric transverse-magnetic splitting to exploit states where these two degrees of freedom are combined. To this end we develop a model based on a spin-orbit Poincaré hypersphere. Then we consider the example of semiconductor polariton systems and demonstrate full ultrafast Stark control of spin-orbit states. Moreover, by controlling states on three different spin-orbit spheres and switching from one sphere to another we demonstrate the control of different logic bits within one single physical system

Vortices in resonant polariton condensates in semiconductor microcavities

Covering general theoretical concepts and the research to date, this book demonstrates that Bose-Einstein condensation is a truly universal phenomenon

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