1,720,966 research outputs found
Weak and strong coupling limits for quantum well polaritons
No full textThe strong and weak coupling regimes are analyzed for quantum well excitons interacting with the light field. The strong-weak coupling transition point is described and quantified in terms of a discrete topological change (from an intersection to an anticrossing) of the quantum well polariton dispersion curves, which occurs at a critical damping rate of excitons
Quantum Theory of Spontaneous Emission in Multilayer Dielectric Structures
No full textThis paper is a theoretical one dealing with spontaneous emission in one-dimensional photonic structures.
We present a fully quantum-electrodynamical formalism suitable to evaluate the spontaneous emission rate and pattern from a dipole embedded in a nonabsorbing and lossless multilayer dielectric structure. In the model here developed the electromagnetic field is quantized by a proper choice of a complete and orthonormal set of classical spatial modes, which consists of guided and radiative (partially and fully) states. In particular, by choosing a set of radiative states characterized by a single outgoing component, we get rid of the problem related to the quantum interference between different outgoing modes, which arises when the standard radiative basis is used to calculate spontaneous emission patterns. After the derivation of the local density of states, the analytical expressions for the emission rates are obtained within the framework of perturbation theory. First we apply our model to realistic silicon-based structures such as a single Si/air interface and a silicon waveguide in both the symmetric and asymmetric configurations. Then, we focus on the analysis of the spontaneous emission process in a silicon-on-insulator (SOI) slot waveguide (a six-layer model structure) doped with Er3+ ions. In this latter case we find a very good agreement with the experimental evidence [M. Galli et al., Appl. Phys. Lett. 89, 241114 (2006)] of an enhanced TM/TE photoluminescence signal. Hence, this model is relevant to study the spontaneous emission in silicon-based multilayer structures which nowadays play a fundamental role for the development of highly integrated multifunctional devices
Instabilities and solitons in systems with spatiotemporal dispersion
No full textA simple model based on the 1D nonlinear Schrodinger equation is studied, which contains both spatially and temporally dispersive terms. Parametric instabilities for plane waves are analyzed in detail, and solitary waves (both bright and dark) are found. The model presented here is able to describe the non-trivial unstable dynamics of intense, nonlinear light propagation near a material resonance in presence of negative spatial dispersion. We provide as a practical example the light propagation near the tail of an exciton-polariton resonance in a specially designed semiconductor superlattice. (C) 2008 Optical Society of America.</p
Strong and weak coupling limits in optics of quantum well excitons
Full text linkA transition between the strong (coherent) and weak (incoherent) coupling limits of resonant interaction between quantum well (QW) excitons and bulk photons is analyzed and quantified as a function of the incoherent damping rate γx caused by exciton-phonon and exciton-exciton scatterings. For confined QW polaritons, a second, anomalous, γx-induced dispersion branch arises and develops with increasing γx. In this case, the strong-weak coupling transition is attributed to γx=γxtr or γ̃xtr, when the intersection of the normal and damping-induced dispersion branches occurs either in {k∥,Im[ω],Re[ω]} coordinate space (in-plane wave vector k∥ is real) or in {ω,Im[k∥],Re[k∥]} coordinate space (frequency ω is real), respectively. For the radiative states of QW excitons, i.e., for radiative QW polaritons, the transition is described as a qualitative change of the photoluminescence spectrum at grazing angles along the QW structure. We show that the radiative corrections to the QW exciton states with in-plane wave vector k∥ approaching the photon cone, i.e., at k∥→k0=(ω0√εb)∕(ℏc) (εb is the background dielectric constant), are universally scaled by the energy parameter (Γ02ω0)1∕3 with Γ0 the intrinsic radiative width and ω0 the exciton energy at k∥=0, rather than diverge. Similarly, the strong-weak coupling transition rates γxtr and γ̃xtr are also proportional to (Γ02ω0)1∕3. The numerical evaluations are given for a GaAs single quantum well with realistic parameters: Γ0=45.5 μeV and (Γ02ω0)1∕3≈1.5 meV
Theoretical and experimental investigation of radiative decay rates in active slot waveguides
No full textIl lavoro è rilevante per la problematica del controllo di emissione spontanea in nanostrutture fotoniche ed in particolare nelle guide d'onda "slot". Viene studiata dal punto di vista sperimentale e teorico l'emissone di luce di Erbio in silicon-rich-oxide (SRO) immerso in guida d'onda di Silicio su Isolante e viene determinata la riduzione del tempo di vita radiativo e non-radiativo. Il lavoro è condotto in collaborazione con l'Università e il centro MATIS-CNR di Catania.
We present a quantum-electrodynamical formalism to study the spontaneous emission from dipoles embedded in a non-absorbing and lossless multilayer dielectric structure. In this model the electromagnetic field is quantized by a proper choice of a complete and orthonormal set of classical modes and the analytical expressions for the emission rates are obtained within the framework of perturbation theory. We apply our model to investigate the 1.54 μm transition of Er3+-doped SiO2 thin layers acting as active material in planar slot waveguides in polycrystalline silicon. The theoretical results show that a strong reduction of the radiative lifetime does occur in the slot waveguide. Furthermore, by using the theoretical analysis together with photoluminescence measurements, we estimate also the radiative efficiency which is found to be only slightly reduced with respect to the value for Er3+ in a bulk of SiO2. These results are important for future realization of silicon-compatible active optical devices and show the relevance of our model to study the spontaneous emission processes in multilayer structures
Modification of erbium radiative lifetime in planar silicon slot waveguides
No full textNel lavoro vengono determinati i tempi di vita radiativi e non radiativi dello ione Erbio in guide d'onda slot con strato sottile di SiO2 in un core di silicio. I risultati sono ottenuti combinando esperimenti con una trattazione teorica quantistica.
The authors report a systematic study of the lifetime of the 1.54 micron transition of Er3+-doped SiO2 thin film as active material in planar slot waveguides in polycrystalline silicon. The lifetime shows a strong reduction when compared with values measured in three other configurations. The experimental results, combined with a rigorous quantum-electrodynamical formalism, are consistent with a sizable increase in both the radiative and nonradiative decay rates of Er3+ transition in slot waveguide. The radiative efficiency is only slightly reduced with respect to Er3+ in the bulk oxide, this result being important for future realization of Si-compatible active optical devices
Microcavity polaritonlike dispersion doublet in resonant Bragg gratings
No full textPeriodic structures resonantly coupled to excitonic media allow the existence of extra intragap modes ("Braggoritons") due to the coupling between Bragg photon modes and bulk excitons. This induces unique dispersive features, which can be tailored by properly designing the photonic band gap around the exciton resonance. We report that Braggoritons realized with semiconductor gratings have the ability to mimic the dispersion of quantum-well microcavity polaritons. This gives rise to peculiar nonlinear phenomena, such as slow-light-enhanced nonlinear propagation and an efficient parametric scattering at two "magic frequencies."</p
Exciton-polaritons in Bragg gratings
No full textWe study the strong coupling between photons and bulk excitons in a one-dimensional Bragg grating. The dispersion of the resulting Bragg-polariton states resembles the dispersion of quantum-well microcavity polaritons. We report on a parametric scattering process at two "magic frequencies" occurring due to the strong excitonic nonlinearity.</p
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