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We report on a new design of terahertz quantum cascade laser based on a single, potential-inserted quantum well active region. The quantum well properties are engineered through single monolayer InAs inserts. The modeling is based on atomistic, spds* tight-binding calculations, and performances are compared to that of the classical three-well design. We obtain a 100% increase of the oscillator strength per unit length, while maintaining a high, nearly temperature-independent contrast between phonon-induced relaxation times of the upper and lower lasing states. The improved performances are expected to allow THz lasing at room temperature. [ABSTRACT FROM AUTHOR]

We evaluate the potential of confined Tamm plasmon structures for single photon extraction. A single quantum dot is inserted in a structure consisting of a gold microdisk deposited on a distributed Bragg reflector. The quantum dot exciton line experiences acceleration of spontaneous emission while the biexciton line experiences inhibition. This property leads to non-linearities in the emission dynamics and the photon statistics as a function of the excitation rate. We show that the device operates as a single photon source with a measured brightness of 0.20 ± 0.02 collected photons per pulse. By modeling the extraction efficiency, we show that efficiencies around 60% can be reached in optimized structures. [ABSTRACT FROM AUTHOR]

The exciton and biexciton lines of a single quantum dot are deterministically coupled to the optical modes of a photonic molecule. The resonance between the quantum dot emission lines and the molecule cavity modes is reached at 53 K. The device operates as a very bright source of entangled photon pairs, with an extraction efficiency of 40% for each photon of the pair. Our measurements show that the use of Purcell effect allows to quench the exciton spin relaxation during the radiative cascade, at 53 K and at high excitation power. [ABSTRACT FROM AUTHOR]

Using low temperature in situ optical lithography, we fabricate pillar microcavities with quality factors around 2×104. Each pillar embeds a spatially and spectrally resonant single InGaAs quantum dot (QD). Light-matter strong coupling regime is reached for 100% of the fabricated pillars for which the resonance can be tuned through temperature. This is a demonstration of scalable and deterministic implementation of strongly coupled cavity-QD devices. [ABSTRACT FROM AUTHOR]

We use optical orientation technique to monitor the degeneracy control of exciton states in a single InAs/GaAs quantum dot, achieved by applying an in-plane electric field. Under circularly polarized quasiresonant excitation, the exciton photoluminescence shows a pronounced maximum of circular polarization at electric field corresponding to zero fine structure splitting. By analyzing the width of this maximum we are able to determine the homogeneous linewidth of the excitonic transition. This experimental method is shown to be very efficient to test and possibly tune the photonic properties of an individual quantum dot for the emission of entangled photon pairs. [ABSTRACT FROM AUTHOR]

The far field radiation pattern of microdisk cavities embedding a quantum well is measured through angle resolved microphotoluminescence. The radiation pattern presents two narrow lobes slightly off the disk plane, in apparent contradiction with previous theoretical predictions. The observed radiation pattern is shown to result from interferences with light reflected by the sample substrate. It can be fully reproduced given the microdisk precise geometry as well as the whispering gallery mode azimuthal number. [ABSTRACT FROM AUTHOR]

The authors report a study of the linear electro-optic coefficient in waveguides containing InGaAs/GaAs quantum dots with a band gap at 1.3 μm. The Pockels effect is investigated in the 1.55 μm telecommunication window. The measured linear electro-optic coefficient for InGaAs/GaAs is ∼3.4×10-11 m/V, much higher than that of the bulk or quantum well material. An ∼35% enhancement of the phase variation is achieved compared to that obtained in bulk GaAs waveguides. Finally, a spectral bandwidth of ∼100 nm is demonstrated in the 1.5–1.6 μm window. [ABSTRACT FROM AUTHOR]

The influence of an in-plane electric field on the optical properties of single quantum dots is investigated. On a sample containing a plane of InAs/GaAs dots, micrometer-size electro-optical structures were produced in order to apply an external electric field in the dot plane. A large decrease of the anisotropic exchange splitting, correlated with the in-plane Stark shift, is observed. [ABSTRACT FROM AUTHOR]

The potential of an InGaAs/GaAs quantum-dot-based phase modulator for broadband (>100 nm) applications at 1.55 µm is demonstrated. A ∼35% enhancement of the phase variation (Vπ ∼ 3.5 V for 4 mm-long devices) is achieved compared to that obtained with bulk GaAs waveguides. [ABSTRACT FROM AUTHOR]

We present measurements of the optical dipole of interband transitions in InAs/GaAs quantum dots. Both the transmission in guided-wave geometry and the in-plane polarization dependence of the photoluminescence are analyzed. The relative oscillator strength and polarization of up to four optical transitions have been determined, and the electronic structure is discussed, with focus on the heavy-hole versus light-hole character of valence states. [Copyright &y& Elsevier]

Giant optical nonlinearity is observed under both continuous wave and pulsed excitation in a deterministically coupled quantum dot-micropillar system, in a pronounced strong-coupling regime. Using absolute reflectivity measurements we determine the critical intracavity photon number as well as the input and output coupling efficiencies of the device. Thanks to a near-unity input-coupling efficiency, we demonstrate a record nonlinearity threshold of only 8 incident photons per pulse. The output-coupling efficiency is found to strongly influence this nonlinearity threshold. We show how the fundamental limit of single-photon nonlinearity can be attained in realistic devices, which would provide an effective interaction between two coincident single-photons. [ABSTRACT FROM AUTHOR]

We demonstrate strong confinement of the optical field by depositing a micron sized metallic disk on a planar distributed Bragg reflector. Confined Tamm plasmon modes are evidenced both experimentally and theoretically, with a lateral confinement limited to the disk area and strong coupling to TE polarized fields. Single quantum dots controllably coupled to these modes are shown to experience acceleration of their spontaneous emission when spectrally resonant with the mode. For quantum dots spectrally detuned from the confined Tamm plasmon mode, an inhibition of spontaneous emission by a factor 40 ± 4 is observed, a record value in the optical domain. [ABSTRACT FROM AUTHOR]

We report on optical orientation of electrons in n-doped InAs/GaAs quantum dots. Under non-resonant cw optical pumping, we measure a negative circular polarization of the luminescence of charged excitons (or trions) at low temperature (T=10 K). The dynamics of the recombination and of the circular polarization is studied by time-resolved spectroscopy. We discuss a simple theoretical model for the trion relaxation, that accounts for this remarkable polarization reversal. The interpretation relies on the bypass of Pauli blocking allowed by the anisotropic electron–hole exchange. Eventually, the spin relaxation time of doping electrons trapped in quantum dots is measured by a non-resonant pump–probe experiment. [Copyright &y& Elsevier]

We have studied the spin dynamics in nonintentionally doped and n-modulation doped self-organized InAs/GaAs quantum dots (QD) by time-resolved photoluminescence. Under strictly resonant excitation, we demonstrate that the carrier spins in these nanostructures are totally frozen on the neutral or charged exciton lifetime scale. In addition, we show that the spin state of the resident electron in n-doped self-assembled InAs–GaAs QD can be written and read using nonresonant, circularly polarized optical pumping. A simple theoretical model is presented and accounts for the remarkable dynamics producing counter-polarized photoluminescence in such structures. [Copyright &y& Elsevier]

We present measurements of electronic spin relaxation and manipulation in n-doped semiconductor quantum dots. A luminescence based nonresonant pump-probe method has been developed to determine the degree of spin polarization of electrons confined in the dots. We observe an electronic spin memory effect up to 20 ns. The mechanism of spin polarization and relaxation are thoroughly analyzed both by continuous wave and time resolved nonresonant luminescence. [Copyright &y& Elsevier]

Abstract: We have studied the variation of photoluminescence circular polarization as a function of temperature in self-organized InAlAs/AlGaAs quantum dots. We have found that the circular polarization depends on temperature. The relaxation time τ s is deduced from the circular polarization degree. It decreases from 2 ns at 40 K to 100 ps at 85 K. [Copyright &y& Elsevier]