Björn M. Möller

Coupled-resonator optical waveguides doped with nanocrystals.

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual cavity modes into coherently coupled waveguide modes is studied using polarization-sensitive microphotoluminescence spectroscopy. To demonstrate the formation of multisphere photon states, we use a bent linear array of microresonators and probe the properties of the cavity photon field by the spatially and spectrally resolved measurement of the nanocrystal emission. Photon mode coupling is evidenced by the observed mode splitting and emission intensity distributions along the CROW structure.

Photons in coupled microsphere resonators

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual resonator modes into coherently coupled waveguide modes is studied using imaging spectroscopy and polarization-sensitive mode mapping. Photon mode coupling is evidenced by the measured mode splittings and emission intensity distributions along the coupled microsphere structure. The observed modifications in both mode splitting and field intensity between odd and even resonator constituents are explained in the frame of a simple coupled-oscillator model. With increasing coupling strength the level splitting increases and the oscillator strength becomes redistributed among the different coupled microsphere states. For each resonator constituent of a six-sphere system a specific mode splitting spectrum is found, in agreement with theoretical predictions.

Mode control by nanoengineering light emitters in spherical microcavities

Quantum-confined semiconductor nanorods are used as highly polarized nanoemitters to actively control the polarization state of microcavity photons. A wet-chemical method to tangentially align CdSe nanorods on a polymer surface is applied to a spherical R≈2λ-microcavity. The cavity emission is studied by imaging spectroscopy and polarization-sensitive mode mapping. The efficient confinement of photons spontaneously emitted by nanorods into single transverse electric (TE) cavity modes is achieved while transverse magnetic modes are suppressed. A microscopic tricolor TE-emitter operating at room temperature in the visible spectral range is demonstrated.

Mode identification in spherical microcavities doped with quantum dots

Using imaging spectroscopy at the diffraction limit, a polarization-sensitive mode mapping allows the experimental identification of transverse electric and transverse magnetic modes for spherical microcavities. The method is applied to microspheres surface covered by CdSe quantum dots. A theoretical estimate of the minimum mode volume excited by a single, anisotropic quantum dot is given with Q/V larger than 1000 μm−3 for the parameters of the experimentally studied microcavities.

Band Formation in Coupled-Resonator Slow-Wave Structures

Sequences of coupled-resonator optical waveguides (CROWs) have been examined as slow-wave structures. The formation of photonic bands in finite systems is studied in the frame of a coupled oscillator model. Several types of resonator size tuning in the system are evaluated in a systematical manner. We show that aperiodicities in sequences of coupled microspheres provide an additional degree of freedom for the design of photonic bands.

Extended and Localized Photon States in 1D-Coupled Resonators

The evolution of individual microsphere-resonator modes into coherently coupled photon states is studied using polarization-sensitive imaging spectroscopy. Photon localization is found both due to Bloch-mode formation and size disorder in agreement with a coupled-oscillator model.