Cavity quantum electrodynamics, a central research field in optics and solid-state physics, addresses properties of atom-like emitters in cavities and can be divided into a weak and a strong coupling regime. For weak coupling, the spontaneous emission can be enhanced or reduced compared with its vacuum level by tuning discrete cavity modes in and out of resonance with the emitter. However, the most striking change of emission properties occurs when the conditions for strong coupling are fulfilled. In this case there is a change from the usual irreversible spontaneous emission to a reversible exchange of energy between the emitter and the cavity mode. This coherent coupling may provide a basis for future applications in quantum information processing or schemes for coherent control. Until now, strong coupling of individual two-level systems has been observed only for atoms in large cavities. Here we report the observation of strong coupling of a single two-level solid-state system with a photon, as realized by a single quantum dot in a semiconductor microcavity. The strong coupling is manifest in photoluminescence data that display anti-crossings between the quantum dot exciton and cavity-mode dispersion relations, characterized by a vacuum Rabi splitting of about 140 microeV.

We demonstrate pronounced single-photon emission from InAs/AlGaInAs/InP quantum dots (QDs) at wavelengths above 1.5 μm that are compatible with standard long-distance fiber communication. The QDs are grown by molecular beam epitaxy on distributed Bragg reflectors. A low QD density of about 5 × 108 cm−2 was obtained using optimized growth conditions. Low-temperature micro-photoluminescence spectroscopy exhibits sharp excitonic emission lines from single QDs without the necessity of further processing steps. The combination of excitation power-dependent and polarization-resolved photoluminescence measurements reveal a characteristic exciton-biexciton behavior with biexciton binding energies that range from 3.5 to 4 meV and fine-structure splitting values down to 20 μeV.

Long wavelength lasers and semiconductor optical amplifiers based on InAs quantum wire-/dot-like active regions were developed on InP substrates dedicated to cover the extended telecommunication wavelength range between 1.4 and 1.65 µm. In a brief overview different technological approaches will be discussed, while in the main part the current status and recent results of quantum-dash lasers are reported. This includes topics like dash formation and material growth, device performance of lasers and optical amplifiers, static and dynamic properties and fundamental material and device modelling.

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We present lasing in optically pumped high-Q micropillar cavity lasers with low thresholds and high β factors. The micropillar cavities with diameters between 1.0 and 4.0μm contain a single layer of low density In0.3Ga0.7As quantum dots as active region. Cavity Q factors of up to 23.000 for 4.0μm micropillar cavities and lasing based on less than 70 quantum dots is demonstrated.

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Vertical-emitting AlAs∕GaAs microcavity pillars with a type of GaInAs quantum dots within a one λ cavity have been realized based on high reflectivity distributed Bragg reflectors. High-quality factors were achieved due to an improved fabrication technology with a maximum quality factor of 27 700 for a micropillar with a diameter of 4μm. The dot dimensions could be enlarged by one order of magnitude using a low strain Ga0.7In0.3As nucleation layer.

We report on molecular beam epitaxy growth of symmetric InAs/InP quantum dots (QDs) emitting at telecom C-band (1.55 µm) with ultra-small excitonic fine-structure splitting of ~2 µeV. The QDs are grown on distributed Bragg reflector and systematically characterized by micro-photoluminescence (µ-PL) measurements. One order of magnitude of QD PL intensity enhancement is observed in comparison with as-grown samples. Combination of power-dependent and polarization-resolved measurements reveal background-free exciton, biexciton and dark exciton emission with resolution-limited linewidth below 35 µeV and biexciton binding energy of ~1 meV. The results are confirmed by statistical measurements of about 20 QDs.