Tilted-potential photonic crystal cavities for integrated quantum photonics.

We propose and investigate a new type of photonic crystal (PhC) cavity for integrated quantum photonics, which provides tailored optical modes with both confined and extended spatial components. The structures consist of elongated PhC cavities in which the effective index of refraction is varied quasi-linearly along their axis, implemented by systematic lateral shifts of the PhC holes. The confined modes have approximately Airy-function envelopes, exhibiting single peaks and extended tails, which is useful for optimizing single photon extraction and transmission in integrated quantum photonic devices. The measured spectrally resolved near-field patterns of such devices show the expected spatial and resonance wavelength behavior, in agreement with numerical simulations of the Airy-Bloch modes. The effects of fabrication-induced disorder on the mode features are also analyzed and discussed. Selective excitation of specific Airy-Bloch modes using integrated, site-controlled quantum dots as localized light sources is demonstrated. Based on the tilted-potential cavity, multiple-QD single photon emitters exploiting wavelength division multiplexing are proposed.

Limiting the Spectral Diffusion of Nano-Scale Light Emitters using the Purcell effect in a Photonic-Confined Environment.

Partial suppression of the spectral diffusion of quantum dot (QD) excitons tuned to resonance of a nano-photonic cavity is reported. The suppression is caused by the Purcell enhancement of the QD-exciton recombination rate, which alters the rate of charging of the solid-state environment by the QD itself. The effect can be used to spectrally-stabilize solid-state emitters of single photons and other non-classical states of light.

Deterministic radiative coupling of two semiconductor quantum dots to the optical mode of a photonic crystal nanocavity.

A system of two site-controlled semiconductor quantum dots (QDs) is deterministically integrated with a photonic crystal membrane nano-cavity. The two QDs are identified via their reproducible emission spectral features, and their coupling to the fundamental cavity mode is established by emission co-polarization and cavity feeding features. A theoretical model accounting for phonon interaction and pure dephasing reproduces the observed results and permits extraction of the light-matter coupling constant for this system. The demonstrated approach offers a platform for scaling up the integration of QD systems and nano-photonic elements for integrated quantum photonics applications.

Effect of Pure Dephasing and Phonon Scattering on the Coupling of Semiconductor Quantum Dots to Optical Cavities.

Using site-controlled semiconductor quantum dots (QDs) free of multiexcitonic continuum states, integrated with photonic crystal membrane cavities, we clarify the effects of pure dephasing and phonon scattering on exciton-cavity coupling in the weak-coupling regime. In particular, the observed QD-cavity copolarization and cavity mode feeding versus QD-cavity detuning are explained quantitatively by a model of a two-level system embedded in a solid-state environment.

Sagliker syndrome: first four cases in Bulgaria.

UNLABELLED: Sagliker syndrome characterized with uglifying the appearance of the face due to secondary hyperparathyroidism in patients with chronic renal failure receiving dialysis long time ago. The aim of the study was to identify any patients with Sagliker syndrome among the 78 patients receiving dialysis at the Dialysis ward, University Hospital "St. George", Plovdiv, Bulgaria. RESULTS: Four patients metthe criteria for Sagliker syndrome: chronic renal insufficiency, secondary hyperparathyroidism, short stature, severe changes in the skull and jaw that lead to festoon-like uglifying face, dental abnormalities, "brown" tumors, deformations of the phalanges of the fingers, psychological diseases and depression. CONCLUSION: The lack of control of the level of calcium and phosphorus in the blood in patients with chronic kidney disease leads to severe bone changes and psychological changes in patients with prolonged dialysis.

25 Gbps direct modulation and 10 km data transmission with 1310 nm waveband wafer fused VCSELs.

Direct modulation at >25 Gbps is achieved with 1310 nm wavelength wafer fused VCSELs by adjusting the strain in the quantum well active region and the cavity photon lifetime. 25 + Gbps large signal modulation with 10-12 BER at 1310 nm across 10 km of standard single mode fiber is demonstrated.

Polarization mode control of long-wavelength VCSELs by intracavity patterning.

Polarization mode control is enhanced in wafer-fused vertical-cavity surface-emitting lasers emitting at 1310 nm wavelength by etching two symmetrically arranged arcs above the gain structure within the laser cavity. The intracavity patterning introduces birefringence and dichroism, which discriminates between the two polarization states of the fundamental transverse modes. We find that the cavity modifications define the polarization angle at threshold with respect to the crystal axes, and increase the gain anisotropy and birefringence on average, leading to an increase in the polarization switching current. Experimental measurements are explained using the spin-flip model of VCSEL polarization dynamics.

8.5 W VECSEL output at 1270 nm with conversion efficiency of 59%.

We report on 1270 nm vertical-external-cavity surface-emitting lasers (VECSELs) with up to 59% conversion efficiency and maximum output power of 8.5 W (pump limited), at 5°C heat sink temperature. These VECSELs comprised wafer-fused gain mirrors in the flip-chip (thin-disk) heat dissipation scheme. The reflected pump light from the gain mirror surface was found to depend considerably on temperature and pump power.

Increasing single mode power of 1.3-µm VCSELs by output coupling optimization.

We report on the single mode emission power enhancement of 1.3-µm VCSELs by adjusting the reflectivity of the top GaAs-based DBR for output coupling optimization using selective removal of Bragg reflector layers. Devices with record single mode power of 6.8-mW at room temperature and 2.8-mW at 80°C, with more than 30 dB single mode suppression ratio, have been obtained.

Optical injection locking of transverse modes in 1.3-µm wavelength coupled-VCSEL arrays.

Optical injection locking of 1.3-µm phase-locked VCSEL arrays defined by patterned tunnel junctions and wafer fusion is investigated experimentally and theoretically. The impact of the overlap between the master laser injection beam and the injected modes is demonstrated and explained with a rate equation model that incorporates the spatial variations.

14XX nm-wavelength electrically-pumped VECSELs fabricated by wafer fusion.

We report on the design, fabrication and characterization of electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs) emitting at 1470 nm. We demonstrate 6.2 mW of CW output power, which represents the highest power value reported so far for EP-VECSELs in the 14XX nm and 15XX nm wavelength bands.

1D and 2D arrays of coupled photonic crystal cavities with a site-controlled quantum wire light source.

We investigated experimentally 1D and 2D arrays of coupled L3 photonic crystal cavities. The optical modes of the coupled cavity arrays are fed by a site-controlled quantum wire light source. By performing photoluminescence measurements and relying on near-field calculation of the cavitiy modes, we evidence optical coupling between the cavities as well as supermode delocalization. In particular, for small cavity separations, fabrication induced disorder effects are shown to be negligible compared to optical coupling between cavities.

Ordered systems of site-controlled pyramidal quantum dots incorporated in photonic crystal cavities.

The coupling of a prescribed number of site-controlled pyramidal quantum dots (QDs) with photonic crystal (PhC) cavities was studied by polarization and power-dependent photoluminescence measurements. The energy of the cavity mode could be readily tuned, making use of the high spectral uniformity of the QDs and designing PhC cavities with different hole radii. Efficient coupling of the PhC cavity modes both to the ground state and to the excited state transitions of the QDs was observed, whereas no evidence for far off-resonant coupling was found.

Symmetries and the polarized optical spectra of exciton complexes in quantum dots.

A systematic and simple theoretical approach is proposed to analyze true degeneracies and polarized decay patterns of exciton complexes in semiconductor quantum dots. The results provide reliable spectral signatures for efficient symmetry characterization, and predict original features for low C(2v) and high C(3v) symmetries. Excellent agreement with single quantum dot spectroscopy of real pyramidal InGaAs/AlGaAs quantum dots grown along [111] is demonstrated. The high sensitivity of biexciton quantum states to exact high symmetry can be turned into an efficient uninvasive postgrowth selection procedure for quantum entanglement applications.

Phonon-mediated coupling of InGaAs/GaAs quantum-dot excitons to photonic crystal cavities.

We demonstrate that the emission characteristics of site-controlled InGaAs/GaAs single quantum dots embedded in photonic crystal slab cavities correspond to single confined excitons coupled to cavity modes, unlike previous reports of similar systems based on self-assembled quantum dots. By using polarization-resolved photoluminescence spectroscopy at different temperatures and a theoretical model, we show that the exciton-cavity interaction range is limited to the phonon sidebands. Photon-correlation and pump-power dependence experiments under nonresonant excitation conditions further establish that the cavity is fed only by a single exciton.

1.38-µm mode-locked Raman fiber laser pumped by semiconductor disk laser.

A mode-locked Raman fiber laser pumped by 1.3 µm semiconductor disk laser is demonstrated. Direct Watt-level core-pumping of the single-mode fiber Raman lasers and amplifiers with low-noise disk lasers is demonstrated to represent a highly practical solution as compared with conventional scheme using pumping by Raman wavelength convertors. Raman laser employing passive mode-locking by nonlinear polarization evolution in normal dispersion regime produces stable pedestal-free 1.97 ps pulses at 1.38 µm. Using semiconductor disk lasers capable of producing high power with diffraction-limited beam allows Raman gain to be obtained at virtually any wavelength of interest owing to spectral versatility of semiconductor gain materials and wafer-fusing technology.

Raman fiber laser pumped by a semiconductor disk laser and mode locked by a semiconductor saturable absorber mirror.

A 1.6µm mode-locked Raman fiber laser pumped by a 1480nm semiconductor disk laser is demonstrated. Watt-level core pumping of the single-mode fiber Raman lasers with low-noise disk lasers together with semiconductor saturable absorber mirror mode locking represents a highly practical solution for short-pulse operation.

Dynamic switching of hole character and single photon polarization using the quantum confined Stark effect in quantum dot-in-dot structures.

The engineering of the three-dimensional (3D) heterostructure potential in GaAs/AlGaAs pyramidal quantum dot-in-dots (DiDs) provides control over the valence band symmetry and hence on the polarization of the emitted photons. We propose a technique for dynamic switching of hole character and photon polarization in DiDs by means of an applied electric field. The structural parameters required for producing this effect are discussed. Asymmetric DiDs are found to be particularly suitable for obtaining switching with fields smaller than 1 kV cm( - 1). The proposed device enables generation of single photons with dynamic control on the photon polarization, with potential applications in quantum information technology.

Dense arrays of ordered pyramidal quantum dots with narrow linewidth photoluminescence spectra.

Arrays of site-controlled, pyramidal InGaAs/GaAs quantum dots (QDs) grown by organo-metallic chemical vapour deposition with densities comparable to those of self-assembled QDs (5 x 10(9) cm(-2)) are demonstrated. The QDs exhibit high quality photoluminescence spectra with inhomogeneous broadening of only 6.5 meV. The QD dipole moment was estimated through the analysis of time-resolved photoluminescence measurements. Such ordered QD arrays should be useful for applications in active nanophotonic systems such as QD lasers, modulators and switches requiring high overlap of the optical modes with the QD active region.

Transition from two-dimensional to three-dimensional quantum confinement in semiconductor quantum wires/quantum dots.

We report the photoluminescence (PL) and polarization-resolved PL characteristics of a novel GaAs/AlGaAs quantum wire/dot semiconductor system, realized by metalorganic vapor-phase epitaxy of site-controlled, self-assembled nanostructures in inverted tetrahedral pyramids. By systematically changing the length of the quantum wires, we implement a continuous transition between the regimes of two-dimensional and three-dimensional quantum confinement. The two main evidences for this transition are observed experimentally and confirmed theoretically: (i) strongly blue-shifted ground-state emission, accompanied by increase separation of ground and excited transition energies; and (ii) change in the orientation of the main axis of linear polarization of the photoluminescence, from parallel to perpendicular with respect to the wire axis. This latter effect, whose origin is shown to be purely due to quantum confinement and valence band mixing, sets in at wire lengths of only approximately 30 nm.