A clock synchronization skeleton based on RTAI

This paper presents a clock synchronization skeleton based on RTAI (Real Time Application Interface). The skeleton is a thin layer that provides unified but extendible interfaces to the underlying operating system, the synchronization algorithms and the upper level applications in need of clock synchronization. The skeleton provides synchronization support to a system, whereby the achieved accuracy is the best obtainable given this software structure. By connecting an algorithm and a communication module with the skeleton, a system becomes capable to run with synchronization support. To demonstrate and validate the design, the skeleton has been tested successfully with two different synchronization algorithms based on the CAN bus. Other algorithms and communication technologies can also work with the skeleton, as long as they provide the necessary functionalities for clock synchronization

Dielectric structures with bound modes for microcavity lasers

Cavity modes of dielectric microspheres and vertical cavity surface emitting lasers, in spite of their high Q, are never exactly bound, but have a finite width due to leakage at the borders. We propose types of microstructures that sustain three-dimensionally bound modes of the radiation field when dissipation is neglected. Unlike photonic crystals, the photonic systems that we consider here rely on periodicity in only one or two dimensions. In particular, we discuss a cavity composed of two crossed vertical layers combined with a periodic structure of horizontal layers. The layers have an anisotropic dielectric tensor, which could be obtained by making air holes in the vertical and horizontal directions within isotropic material. We calculate cavity resonance frequencies and spontaneous emission rates. The simplicity of this laser geometry allows an analytical study of light propagation and amplification in three dimensions

Entangled photons from small quantum dots

We discuss level schemes of small quantum-dot turnstiles and their applicability in the production of entanglement in two-photon emission. Due to the large energy splitting of the single-electron levels, only one single-electron level and one single-hole level can be made resonant with the levels in the conduction band and valence band. This results in a model with nine distinct levels, which are split by the Coulomb interactions. We show that the optical selection rules are different for flat and tall cylindrically symmetric dots, and how this affects the quality of the entanglement generated in the decay of the biexciton state. The effect of charge-carrier tunneling and of a resonant cavity is included in the model