The authors investigate the multiple confined modes of GaAs L3 photonic crystal air-bridge cavities, using single layers of InAs quantum dots as active internal light sources. Theoretical results for the energies, quality factors, and emission polarizations of the first five modes are compared to experimental data for cavities with lattice periods ranging from 240to270nm. The authors also present in-plane field distributions for each mode. In addition to the well-known quality factor improvement of the fundamental mode, they show that outward displacement of the end-holes selectively redshifts modes with large end-hole-field overlaps, thus reordering the modes.

Abstract:We investigate the energy splitting, quality factor and polarization of the fundamental modes of coupled L3 photonic crystal cavities. Four different geometries are evaluated theoretically, before experimentally investigating coupling in a direction at 30 • to the line of the cavities. In this geometry, a smooth variation of the energy splitting with the cavity separation is predicted and observed, together with significant differences between the polarizations of the bonding and anti-bonding states. The controlled splitting of the coupled states is potentially useful for applications that require simultaneous resonant enhancement of two transitions. This compares with V = 0.76(λ /n) 3 for an isolated cavity in the same lattice. 20. Three other modes exist between the + − 1 and − − 2 modes. Unfortunately, the close spacings and low quality factors of these other modes [18] make it impractical to identify their peaks unambiguosly in Fig. 3. It is, however, likely that the predicted 1.5 meV splitting of the + + 1 mode is responsible for the most prominent features; the predicted splittings of the other two modes are insufficient to explain the peak around 1.32 eV. 21. Note that the results for the FDTD simluations become inaccurate for the largest cavity separation, since the intensity above the center of the double cavity becomes very low. 22. E. Gallardo, L. J. Martínez, A. K. Nowak, H. P. van der Meulen, J. M. Calleja, C. Tejedor, I. Prieto, D. Granados, A. G. Taboada, J. M. García, and P. A. Postigo, "Emission polarization control in semiconductor quantum dots coupled to a photonic crystal microcavity," Opt. Express 18, 13301-13308 (2010).

We study the linear polarization of the emission from single quantum dots embedded in an "L3" defect nanocavity in a two-dimensional photonic crystal. By using narrow linewidth optical excitation in resonance with higher-order modes, we are able to achieve strong quantum dot emission intensity whilst reducing the background from quantum dots in the surrounding lattice. We find that all the dots observed emit very strongly linearly polarized light of the same orientation as the closest mode, despite the fact that these quantum dots may be spectrally detuned by several times the mode linewidth. We discuss the coupling mechanisms which may explain this behavior.

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