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Nanophotonic structures combining electronic confinement in nanocrystals with photon confinement in photonic structures are potential building blocks of future Si-based photonic devices. Here, we present a detailed optical investigation of active planar waveguides fabricated by Si + -ion implantation (400 keV, fluences from 3 to 6×10 17 cm −2 ) of fused silica and thermally oxidized Si wafers. Si nanocrystals formed after annealing emit red-IR photoluminescence (PL) (under UV-blue excitation) and define a layer of high refractive index that guides part of the PL emission. Light from external sources can also be coupled into the waveguides (directly to the polished edge facet or from the surface by applying a quartz prism coupler). In both cases the optical emission from the sample facet exhibits narrow polarization-resolved transverse electric and transverse magnetic modes instead of the usual broad spectra characteristic of Si nanocrystals. This effect is explained by a theoretical model which identifies the microcavity-like peaks as leaking modes propagating below the waveguide/substrate boundary. We present also permanent changes induced by intense femtosecond laser exposure, which can be applied to write structures like gratings into the Si-nanocrystalline waveguides. Finally, we discuss the potential for application of these unconventional and relatively simple all-silicon nanostructures in future photonic devices.

In CuCl, biexcitons may be excited from the semiconductor ground state by two circularly polarized exciton polaritons of opposite helicity. We use this property to develop a new method in order to determine the spin-relaxation dynamics by means of non-degenerate pump–probe experiments. A pump beam first excites a spin-polarized exciton population. Then, we measure the induced absorption of a circularly polarized probe beam at the exciton biexciton transition. It depends on its polarization and the induced absorption dynamics gives information on the spin state of the exciton polariton population. When comparing results obtained in a (σ + σ + ) configuration with that of a (σ + σ − ) configuration, we determine the time evolution of the pseudo-spin of the exciton polaritons as well as their lifetime.