Non-linear photonic crystals as a source of entangled photons

Non-linear photonic crystals can be used to provide phase-matching for frequency conversion in optically isotropic materials. The phase-matching mechanism proposed here is a combination of form birefringence and phase velocity dispersion in a periodic structure. Since the phase-matching relies on the geometry of the photonic crystal, it becomes possible to use highly non-linear materials. This is illustrated considering a one-dimensional periodic Al$_{0.4}$Ga$_{0.6}$As / air structure for the generation of 1.5 $\mu$m light. We show that phase-matching conditions used in schemes to create entangled photon pairs can be achieved in photonic crystals.Comment: 4 pages, 3 figure

Photon statistics from coupled quantum dots

We present an optical study of closely-spaced self-assembled InAs/GaAs quantum dots. The energy spectrum and correlations between photons subsequently emitted from a single pair provide not only clear evidence of coupling between the quantum dots but also insight into the coupling mechanism. Our results are in agreement with recent theories predicting that tunneling is largely suppressed between nonidentical quantum dots and that the interaction is instead dominated by dipole-dipole coupling and phonon-assisted energy transfer processes.Comment: 4 pages, 4 figures, to appear in Phys. Re

Measurement of the Phase and Intensity Profile of Surface Plasmon Laser Emission

We study the near- and far-field radiation patterns of surface plasmon (SP) lasers in metal hole arrays and observe radially polarized vortex-vector laser beams in both near and far field. Besides the intensity profile, also the complementary phase profile is obtained with a beam block experiment, where we block part of the beam in the near field, measure the resulting changes in the far field, and retrieve the phase using an iterative algorithm. This phase profile provides valuable information on the feedback mechanisms and coherence of the laser and shows that our SP laser operates in a phase-slip mode instead of a pure dark mode. To explain our observations, we extend the standard model for distributed feedback lasers by introducing a position dependence in the optical gain and refractive index