Photonic molecules have been fabricated by coupling pairs of micrometer-sized semiconductor cavities via a narrow channel. The optical modes in these structures have been studied spectroscopically as a function of the coupling and the mode energies are compared to detailed calculations. These results provide a rich picture of photonic modes in these molecules. [S0031-9007(98)

We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.

The optical modes of chains of coupled micron sized semiconductor cavities have been studied using photoluminescence spectroscopy and detailed calculations. With an increasing number of cavities, the chains exhibit photon band gaps at several Brillouin zone boundaries. The sizes of the band gaps are shown to depend on the coupling between the microcavities and also on the order of the Brillouin zone involved. PACS numbers: 78.55.Cr, 42.70.Qs Systems which exhibit photon band gaps analogous to the band gaps in the electronic states of periodic solids have been the subject of intense investigations in the past decade [1][2][3]. In the photonic case, the forbidden energy gaps in the frequency spectrum result from a periodic modulation of the refractive index. These systems are called "photonic crystals" and calculations of their properties for a number of structures have been made [1,2,4]. They permit the coupling between photons and electronic excitations to be studied and controlled in powerful ways, including the introduction of highly localized defect modes in the band gaps.Experimentally, to date photonic crystals have been realized over several parts of the electromagnetic spectrum [5][6][7][8][9][10][11][12][13][14]. The near infrared and the visible range is particularly important for potential applications as well as for fundamental studies [15,16]. Photonic crystals could be used, for example, to obtain semiconductor lasers with zero, or low, threshold due to the possibility of suppressing the spontaneous emission by photonic energy gaps. Defect modes in band gaps are of interest in connection with waveguides for ultrasmall integration.Recently it has been shown that micron sized semiconductor resonator cavities exhibit sharp photonic resonances resulting from the strong optical confinement in all three directions [17][18][19]. The vertical confinement of the photon modes is effected by Bragg mirrors, and the lateral confinement is caused by etching of the cavity. In this way, strong photonic resonances are created in the cavities whose energies are controlled by the cavity size. These modes are analogous to the sharp electronic states of atoms or quantum dots.In the present work we have created a photonic band gap system for frequencies in the near infrared by putting together microcavities in chains. We are able to construct a system by adding individual building blocks ("photonic atoms") one by one. Angle-resolved photoluminescence spectroscopy is used to study the emergence of a photonic band structure: In chains formed from an increasing number of cavities we observe a transition from discrete atomiclike modes to the photonic band structure of a solid with band gaps at several Brillouin zone boundaries. We are able to modify the modulation of the refractive index by varying the coupling between the cavities, and the energy gaps are found to increase with increasing modulation. We show that the experimental results are in quantitative agreement with numerical calculations of the photonic band struct...

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