Near-field to far-field transition of photonic crystal fibers: symmetries and interference phenomena

The transition from the near to the far field of the fundamental mode radiating out of a photonic crystal fiber is investigated experimentally and theoretically. It is observed that the hexagonal shape of the near field rotates two times by pi/6 when moving into the far field, and eventually six satellites form around a nearly gaussian far-field pattern. A semi-empirical model is proposed, based on describing the near field as a sum of seven gaussian distributions, which qualitatively explains all the observed phenomena and quantitatively predicts the relative intensity of the six satellites in the far field.Comment: 7 pages including 6 figures. Animated version of Fig. 5 is available at http://www.crystal-fibre.com/technology/movie.gi

Optical properties of InAlGaAs quantum wells: Influence of segregation and band bowing

Knowledge of the quaternary InAlGaAs material system is very limited for the composition range relevant for growth on GaAs substrates. We report on the characterization and modeling of InAlGaAs quantum wells with AlGaAs barriers, grown pseudomorphically on a GaAs substrate with molecular beam epitaxy. The quantum wells are characterized with photoluminescence, and the measured transition energies are modeled taking into account the influence of In segregation on the shape of the well potential. From the modeling we deduce a relation for the low temperature band gap of unstrained Inx(AlyGa1−y)1−xAs, for 0⩽x,y⩽0.20. The measured linewidths of the luminescence peaks are in agreement with the broadening expected from random alloy fluctuations and well width fluctuations with an effective interface roughness of 1.1 ML

Ultranarrow polaritons in a semiconductor microcavity

We have achieved a record high ratio (19) of the Rabi splitting (3.6 meV) to the polaritonlinewidth (190 μeV), in a semiconductor λ microcavity with a single 25 nm GaAsquantum well at the antinode. The narrow polariton lines are obtained with a special cavity design which reduces the exciton broadening due to scattering with free charges and has a very low spatial gradient of the cavity resonance energy. Since the static quantum-well disorder is very small, the polariton broadening is dominantly homogeneous. Still, the measured linewidths close to zero detuning cannot be correctly predicted using the linewidth averaging model