Self-organized synthetic opals possessing a face centered cubic (fcc) lattice are promising for fabrication of a three-dimensional photonic crystal with a full photonic band gap in the visible. The fundamental limiting factor of this method is the large concentration of lattice defects and, especially, planar stacking faults, which are intrinsic to self-assembling growth of colloidal crystal. We have studied the influence of various types of defects on photonic band structure of synthetic opals by means of optical transmission, reflection and diffraction along different crystallographic directions. We found that in carefully chosen samples the stacking probability alpha can be as high as 0.8-0.9 revealing the strong preference of fcc packing sequence over the hexagonal close-packed (hcp). It is shown that scattering on plane stacking faults located perpendicular to the direction of growth results in a strong anisotropy of diffraction pattern as well as in appearance of a pronounced doublet structure in transmission and reflection spectra taken from the directions other than the direction of growth. This doublet is a direct manifestation of the coexistence of two crystallographic phases--pure fcc and strongly faulted. As a result the inhomogeneously broadened stop-bands overlap over a considerable amount of phase space. The latter, however, does not mean the depletion of the photonic density of states since large disordering results in filling of the partial gaps with both localized and extended states.

Optical spin-dynamic measurements in a high-mobility n-doped GaAs/AlGaAs quantum well show oscillatory evolution at 1.8 K consistent with a quasi-collision-free D'yakonov-Perel'-Kachorovskii regime. Above 5 K evolution becomes exponential as expected for collision-dominated spin dynamics. Momentum scattering times extracted from Hall mobility and Monte Carlo simulation of spin polarization agree at 1.8 K but diverge at higher temperatures, indicating the importance of electron-electron scattering and an intrinsic upper limit for the spin-relaxation rate.

Time-resolved optical measurements in (110)-oriented GaAs/AlGaAs quantum wells show a tenfold increase of the spin-relaxation rate as a function of applied electric field from 20 to 80 kV cm(-1) at 170 K and indicate a similar variation at 300 K, in agreement with calculations based on the Rashba effect. Spin relaxation is almost field independent below 20 kV cm(-1) reflecting quantum well interface asymmetry. The results indicate the achievability of a voltage-gateable spin-memory time longer than 3 ns simultaneously with a high electron mobility.

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We demonstrate an on-demand single-photon source that is compatible with standard telecom optical fiber. Through careful control of the critical strains of InAs∕GaAs self-assembled quantum dots, we produce a microcavity sample with a low density of large dots emitting into the fiber-optic transmission band at 1.3μm. The second-order correlation function of the source reveals a strong suppression in the rate of multiphoton pulses at both 5K and above 30K. The source may be useful for fiber-optic-based single-photon applications, such as quantum metrology, quantum communications, and distributed quantum computing.