Towards Low Cost Coupling Structures for Short-Distance Optical Interconnections

The performance of short distance optical interconnections in general relies very strongly on coupling structures, since they will determine the overall efficiency of the system to a large extent. Different configurations can be considered and a variety of manufacturing technologies can be used. We present two different discrete and two different integrated coupling components which can be used to deflect the light beam over 90 degrees and can play a crucial role when integrating optical interconnections in printed circuit boards. The fabrication process of the different coupling structures is discussed and experimental results are shown. The main characteristics of the coupling structures are given. The main advantages and disadvantages of the different components are discussed

Visualisation and les simulation of cavitation cloud formation and collapse in an axisymmetric geometry

Visualisation and Large Eddy Simulations (LES) of cavitation inside the apparatus previously developed by Franc (2011) for surface erosion acceleration tests and material response monitoring are presented. The experimental flow configuration is a steady-state closed loop flow circuit where pressurised water, flowing through a cylindrical feed nozzle, is forced to turn 90° and then, move radially between two flat plates towards the exit of the device. High speed images show that cavitation is forming at the round exit of the feed nozzle. The cavitation cloud then grows in the radial direction until it reaches a maximum distance where it collapses. Due to the complexity of the flow field, direct observation of the flow structures was not possible, however vortex shedding is inferred from relevant simulations performed for the same conditions. Despite the axisymmetric geometry utilized, instantaneous pictures of cavitation indicate variations in the circumferential direction. Image post-processing has been used to characterize in more detail the phenomenon. In particular, the mean cavitation appearance and the cavity length have been estimated, showing good correlation with the erosion zone. This also coincides with the locations of the maximum values of the standard deviation of cavitation presence. The dominant frequency of the ‘large-scale’ cavitation clouds has been estimated through FFT. Cloud collapse frequencies vary almost linearly between 200 and 2000 Hz as function of the cavitation number and the downstream pressure. It seems that the increase of the Reynolds number leads to a reduction of the collapse frequency; it is believed that this effect is due to the agglomeration of vortex cavities, which causes a decrease of the apparent frequency. The results presented here can be utilized for validation of relevant cavitation erosion models which are currently under development

Electrical properties of CdTe near the melting point

A new experimental setup for the investigation of electrical conductivity (σ) in liquid and solid CdTe was built for a better understanding of the properties near the melting point (MP). The temperature dependence of σ was studied, within the interval 1,050-1,130°C, at defined Cd-partial pressures 1.3-1.6 atm, with special attention to the liquid-solid phase transition. We found that the degree of supercooling decreases with increasing Cd overpressure and reaches the lowest value at 1.6 atm without change of the melting temperature during heating

A Carleman type theorem for proper holomorphic embeddings

In 1927, Carleman showed that a continuous, complex-valued function on the real line can be approximated in the Whitney topology by an entire function restricted to the real line. In this paper, we prove a similar result for proper holomorphic embeddings. Namely, we show that a proper \cC^r embedding of the real line into \C^n can be approximated in the strong \cC^r topology by a proper holomorphic embedding of \C into \C^n

Opto-PCB: Three demonstrators for optical interconnections

We report on a research project targeting optical waveguide integrated PCBs conducted within the European FP6 Network of Excellence on Micro-Optics NEMO. For three identified feature requests we have built three specific demonstrators respectively addressing the integration of active components, the fabrication of peripheral fibre ribbons and the integration of multiple layers of waveguides on the board

High temperature mobility of CdTe

The Hall mobility of electrons μH is measured in CdTe in the temperature interval 450-1050°C and defined Cd overpressure in near-intrinsic conditions. The strong decrease of μH above 600°C is reported. The effect is explained within a model of multivalley conduction where both electrons in �1c minimum and in L1c minima participate. The theoretical description is based on the solution of the Boltzmann transport equation within the relaxation time approximation including the polar and acoustic phonon intravalley and intervalley scatterings. The �1c to L1c separation �E=0.29 - 10-4T (eV) for the effective mass in the L valley mL=0.35m0 is found to best fit the experimental data. Such �E is about four times smaller than it is predicted by first-principle calculations. © 2001 American Institute of Physics

Numerical simulation of cavitation and atomization using a fully compressible three-phase model

The aim of this paper is to present a fully compressible three-phase (liquid, vapour and air) model and its application to the simulation of in-nozzle cavitation effects on liquid atomization. The model employs a combination of homogeneous equilibrium barotropic cavitation model with an implicit sharp interface capturing VoF approximation. The numerical predictions are validated against the experimental results obtained for injection of water into the air from a step-nozzle, which is designed to produce asymmetric cavitation along its two sides. Simulations are performed for three injection pressures, corresponding to three different cavitation regimes, referred to as cavitation inception, developing cavitation and hydraulic-flip. Model validation is achieved by qualitative comparison of the cavitation, spray pattern and spray cone angles. The flow turbulence in this study is resolved using the Large Eddy Simulation approach. The simulation results indicate that the major parameters that influence the primary atomization are cavitation, liquid turbulence and, to a smaller extent, the Rayleigh-Taylor and Kelvin-Helmholtz aerodynamic instabilities developing on the liquid/air interface. Moreover, the simulations performed indicate that periodic entrainment of air into the nozzle occurs at intermediate cavitation numbers, corresponding to developing cavitation (as opposed to incipient and fully-developed cavitation regimes); this transient effect causes a periodic shedding of the cavitation and air clouds and contributes to improved primary atomization. Finally, the cone angle of the spray is found to increase with increased injection pressure but drops drastically when hydraulic-flip occurs, in agreement with the relevant experiments

A Universal Scaling Law for Jets of Collapsing Bubbles

Cavitation bubbles collapsing and rebounding in a pressure gradient grad(p) form a "micro-jet" enveloped by a "vapor jet". This letter presents unprecedented observations of the vapor jets formed in a uniform gravity-induced grad(p), modulated aboard parabolic flights. The data uncovers that the normalized jet volume is independent of the liquid density and viscosity and proportional to zeta=grad(p)*R0/p, where R0 is the maximal bubble radius and p is the driving pressure. A derivation inspired by "Kelvin-Blake" considerations confirms this law and reveals its negligible dependence of surface tension. We further conjecture that the jet only pierces the bubble boundary if zeta>0.0004.Comment: 4 page letter, 4 figure