Defects in one-dimensional photonic crystals have been studied by angle-resolved photoluminescence spectroscopy from which we obtain a comprehensive picture of the energies and field distributions of modes in the photon band gaps. The structures have been fabricated by coupling semiconductor microcavities that exhibit an index confinement of light in all three directions to linear chains. The defects are obtained by varying the size of one of the microcavities in the chain. Time-resolved spectroscopy demonstrates that the decay rate of the spontaneous emission of quantum dots into a defect mode is considerably enhanced ͑Purcell effect͒.
Isomeric photonic molecules were formed by connecting four identical cavities in different geometries: a chain, a square, and a T shape. The optical mode spectrum in these structures exhibits three-dimensionally confined photonic states, which have been studied by photoluminescence spectroscopy. The energies of the optical modes depend strongly on the molecule geometry. The experimental data are in good agreement with detailed calculations of the fields in the cavities.
A scanning near-field microscope design using the reflected light intensity as the feedback mechanism is described. Multiple fibers with high numerical apertures provide a high collection efficiency in a reflection geometry. The performance with regard to its response to large spatial variations has been tested by using a Si-grating sample and with regard to variations of local indices of refraction by using GaAs/AlGaAs heterostructure samples. In addition, spatially resolved spectroscopy on GaAs/AlGaAs heterostructures has been obtained.
The luminescence of GaAs quantum-well-based microstructures was investigated with a scanning near-field optical microscope at different ambient temperatures. The scanning tip was fabricated from an optical fiber. The excitation laser beam (514 nm, 100–300 mW) was focused onto the opposite end of the fiber. The carrier distribution in the sample was investigated using the high-energy tail of the luminescence peak. Temperature fits show no overheating of the sample despite the expected high temperatures of the tip.
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