Unconditional Continuous Variable Dense Coding

We investigate the conditions under which unconditional dense coding can be achieved using continuous variable entanglement. We consider the effect of entanglement impurity and detector efficiency and discuss experimental verification. We conclude that the requirements for a strong demonstration are not as stringent as previously thought and are within the reach of present technology

Employing Channel Probing to Derive End-of-Life Service Margins for Optical Spectrum Services

Optical Spectrum as a Service (OSaaS) spanning over multiple transparent optical network domains, can significantly reduce the investment and operational costs of the end-to-end service. Based on the black-link approach, these services are empowered by reconfigurable transceivers and the emerging disaggregation trend in optical transport networks. This work investigates the accuracy aspects of the channel probing method used in Generalized Signal to Noise Ratio (GSNR)-based OSaaS characterization in terrestrial brownfield systems. OSaaS service margins to accommodate impacts from enabling neighboring channels and end-of-life channel loads are experimentally derived in a systematic lab study carried out in the Open Ireland testbed. The applicability of the lab-derived margins is then verified in the HEAnet production network using a 400 GHz wide OSaaS. Finally, the probing accuracy is tested by depleting the GSNR margin through power adjustments utilizing the same 400 GHz OSaaS in the HEAnet live network. A minimum of 0.92 dB and 1.46 dB of service margin allocation is recommended to accommodate the impacts of enabling neighboring channels and end-of-life channel loads. Further 0.6 dB of GSNR margin should be allocated to compensate for probing inaccuracies

Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (ie when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a better resolution in the published version. New version reflects minor changes brought after proof editin

Overcoming degradation in spatial multiplexing systems with stochastic nonlinear impairments

Single-mode optical fibres now underpin telecommunication systems and have allowed continuous increases in traffic volume and bandwidth demand whilst simultaneously reducing cost- and energy-per-bit over the last 40 years. However, it is now recognised that such systems are rapidly approaching the limits imposed by the nonlinear Kerr effect. To address this, recent research has been carried out into mitigating Kerr nonlinearities to increase the nonlinear threshold and into spatial multiplexing to offer additional spatial pathways. However, given the complexity associated with nonlinear transmission in spatial multiplexed systems subject to random inter-spatial-path nonlinearities it is widely believed that these technologies are mutually exclusive. By investigating the linear and nonlinear crosstalk in few-mode fibres based optical communications, we numerically demonstrate, for the first time, that even in the presence of significant random mixing of signals, substantial performance benefits are possible. To achieve this, the impact of linear mixing on the Kerr nonlinearities should be taken into account using different compensation strategies for different linear mixing regimes. For the optical communication systems studied, we demonstrate that the performance may be more than doubled with the appropriate selection of compensation method for fibre characteristics which match those presented in the literature

Physics of Solar Prominences: II - Magnetic Structure and Dynamics

Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape

Diffraction from oxide confinement apertures in vertical-cavity lasers

Includes bibliographical references (page 756).Direct measurement of scattered fields from oxide confinement apertures in vertical-cavity lasers is presented. Diffraction fringes associated with each transverse lasing mode are detected in the far field from devices with varying oxide aperture dimensions and with quantum efficiencies as high as 48%. The diffracted pattern symmetries match the rectangular symmetry of the oxide apertures present in the devices and fringe locations are compared to Fraunhofer theory. The fraction of power diffracted from the lasing mode remains roughly constant as a function of relative pump rate, but is shown to depend on both transverse mode order and oxide aperture size.This work was supported by the NSF–EPSCOR, NASA–EPSCOR, ILX Lightwave, and the DOE

Microcrystalline silicon deposition process stability and process control

Applying in situ process diagnostics, we identified several process drifts occurring in the parallel plate plasma deposition of microcrystalline silicon (mu c-Si:H). These process drifts are powder formation (visible from diminishing dc-bias and changing spatial emission profile on a time scale of 10(0) s), transient SiH4 depletion (visible from a decreasing SiH emission intensity on a time scale of 10(2) s), plasma heating (visible from an increasing substrate temperature on a time scale of 10(3) s) and a still puzzling long-term drift (visible from a decreasing SiH emission intensity on a time scale of 10(4) s). The effect of these drifts on the crystalline volume fraction in the deposited films is investigated by selected area electron diffraction and depth-profiled Raman spectroscopy. An example shows how the transient depletion and long-term drift can be prevented by suitable process control. Solar cells deposited using this process control show enhanced performance. Options for process control of plasma heating and powder formation are discussed. (C) 2007 Elsevier B.V. All rights reserved