Klaas Allaart

Spontaneous emission in a V-type three-level atom driven by a classical field

Abstract We have studied the spectrum of spontaneous emission of a V-configuration three-level atom, whose two upper levels are linked by a classical driving field and their energy spacing is much larger than the spontaneous emission widths. It is shown that the spectrum can be controlled by the driving field and peaks with subnatural linewidth can be produced.

Spontaneous emission in multilayer semiconductor structures

A theoretical analysis of spontaneous emission from a quantum well in dielectric multilayer structures, especially the influence of dielectric geometry on the relative intensities of guided and radiation modes and on polarization, is presented. We first discuss a relatively simple three-layer case, and subsequently a technologically more interesting five-layer structure that has been proposed for a high-power laser. The expression for the partial as well as total, emission rates is derived within a broader framework of coupled Heisenberg equations of motion for charge carriers and the quantized electromagnetic field. Thereby, the explicit mode decomposition of the Green tensor is avoided. Still, the beta factor for individual guided modes, which is a relevant quantity for the lasing threshold of a device, can be identified and a competition between modes is shown to exist in specific cases.

Entangled photons from small quantum dots

We discuss level schemes of small quantum-dot turnstiles and their applicability in the production of entanglement in two-photon emission. Due to the large energy splitting of the single-electron levels, only one single-electron level and one single-hole level can be made resonant with the levels in the conduction band and valence band. This results in a model with nine distinct levels, which are split by the Coulomb interactions. We show that the optical selection rules are different for flat and tall cylindrically symmetric dots, and how this affects the quality of the entanglement generated in the decay of the biexciton state. The effect of charge-carrier tunneling and of a resonant cavity is included in the model.

Bound modes in dielectric microcavities

We demonstrate how exactly bound cavity modes can be realized in dielectric structures other than 3D photonic crystals. For a microcavity consisting of crossed anisotropic layers, we derive the cavity resonance frequencies, and spontaneous emission rates. For a dielectric structure with dissipative loss and central layer with gain, the β factor of direct spontaneous emission into a cavity mode and the laser threshold is calculated.

Properties of spontaneous emission in semiconductor structures

A quantum mechanical description is presented of the electromagnetic field produced by a semiconductor quantum well within a passive dielectric multilayer structure. The method is suitable to deal with relatively complicated structures as it avoids an explicit mode decomposition of the electromagnetic field. Instead, only the classical Greens tensor, which is characteristic of a certain passive structure, is required. Our central result is a general expression for the spontaneous emission rate, that we apply to a quantum well embedded in a three-layer (waveguide) structure. The dependence of the spontaneous emission rate on the thickness of the middle layer, or on the position of the quantum well in it, is shown to be smooth. But the separate continuous (radiation modes) and discrete (guided modes) contributions to this rate show peculiar cusps as a function of this thickness, and these discontinuities are analyzed.

Model simulations of a reflective semiconductor optical amplifier

A reflective semiconductor optical amplifier is modeled using a rate equation for the inversion and an expression for the outgoing field in terms of the incoming field and the instantaneous inversion, for both the cases of linear and nonlinear gain, while assuming modulation speeds well below the round-trip frequency. Simulations are performed on the basis of these equations. Results for both the static and dynamic performance are presented and discussed.

Ultrafast birefringence in semiconductor optical amplifier due to the carrier momentum orientation relaxation

This paper reports ultrafast birefringence dynamics in a semiconductor optical amplifier on subpicosecond or even femtosecond time scales. This is due to the carrier momentum orientation relaxation, induced by a polarized short optical pulse

Gain anisotropy in a semiconductor optical amplifier: confinement factors or material gain

We show that if gain anisotropy in a bulk semiconductor optical amplifier (SOA) is attributed to different confinement factors for the TE and TM modes, the anisotropy as a function of pump current is quite different from the case when another mechanism, material gain anisotropy due to weak strain in the active layer, is the cause of anisotropy. With a simple model for the latter mechanism we obtain a good description of trends seen in a recent experiment and give a prescription for the phenomenological hole reservoir anisotropy factor f that has been introduced before in model simulations.

Twin photons from small quantum dots

Due to the large energy splitting of the single-electron levels in a small quantum dot, only one single electron level and one single hole level can be made resonant with the levels in the conduction band and valence band. This results in a closed system with nine distinct levels, which are split by the Coulomb interactions. We show that flat and tall cylindrically symmetric dots have level schemes with different selection rules. In both cases entangled photon pairs can be efficiently produced.