Round-trip time and dispersion optimization in a dual-wavelengthactively mode-locked Er-doped fiber laser including nonchirped fiberBragg gratings

Round-trip time and intracavity dispersion were optimized in a dual-wavelength actively mode-locked Er-doped fiber laser including two nonchirped fiber Bragg gratings. This optimization allowed to generate nearly transform-limited pulses as short as 16 and 13 ps at 1547 and 1562 nm, respectively, at a 3-GHz repetition rate only limited by the modulator bandwidth. In the experiment, the round-trip time difference between pulses at two wavelengths was adjusted using a fiber stretcher. Intracavity dispersion was managed at each wavelength separately     

Practical technique for measurement of second-order nonlinearity in poled glass

A simple and nondestructive technique for measuring the thickness of the nonlinear optical layer in thermally poled glass, providing a minimum measurable thickness of 4 and 1 /spl mu/m resolution, is demonstrated. This technique is generally applicable to other nonlinear optical layers as well.     

UWB in Millimeter Wave Band With Pulsed ILO

A simple but efficient transmitter for ultra-wide-band impulse radio wavelet generator in millimeter-wave band is presented. It is suitable for RADAR, gigabit wireless personal area network, and localization applications. This front-end involves a subharmonic injection-locked oscillator driven by a pulse generator (PG) with fast transition time (<25 ps). Its frequency oscillation is locked on one of the numerous harmonic components generated by the PG around 30 GHz. This allows to obtain a stable pulse-to-pulse phase condition and a very low phase noise (<-110 dBc/Hz@100 kHz). Two monolithic microwave integrated circuits have been designed using a commercial pseudomorphic high-electron mobility transistor foundry process (ft = 100 GHz). The first one is a PG with position and width modulation capabilities, and the second one is an oscillator with a 30-GHz free-running output frequency. The start of the oscillations is studied, using the external quality factor as main factor.     

A Monolithic Approach to Fluid–Composite Structure Interaction

We study a nonlinear fluid–structure interaction (FSI) problem between an incompressible, viscous fluid and a composite elastic structure consisting of two layers: a thin layer (membrane) in direct contact with the fluid, and a thick layer (3D linearly elastic structure) sitting on top of the thin layer. The coupling between the fluid and structure, and the coupling between the two structures is achieved via the kinematic and dynamic coupling conditions modeling no-slip and balance of forces, respectively. The coupling is evaluated at the moving fluid–structure interface with mass, i.e., the thin structure. To solve this nonlinear moving-boundary problem in 3D, a monolithic, fully implicit method was developed, and combined with an arbitrary Lagrangian–Eulerian approach to deal with the motion of the fluid domain. This class of problems and its generalizations are important in e.g., modeling FSI between blood flow and arterial walls, which are known to be composed of several different layers, each with different mechanical characteristics and thickness. By using this model we show how multi-layered structure of arterial walls influences the pressure wave propagation in arterial walls, and how the presence of atheroma and the presence of a vascular device called stent, influence intramural strain distribution throughout different layers of the arterial wall. The detailed intramural strain distribution provided by this model can be used in conjunction with ultrasound B-mode scans as a predictive tool for an early detection of atherosclerosis (Zahnd et al. in IEEE international on ultrasonics symposium (IUS), pp 1770–1773, 2011).     

An Impulse System for 60-GHz Wireless Networks Based on Polymer Optical Fiber

A specific impulse optical fiber system has been achieved to enhance the connectivity of 60-GHz wireless networks. Using an impulse technology, this original configuration is an efficient alternative to the conventional 60-GHz radio-over-fiber systems. Baseband subnanosecond pulses first modulate the amplitude of a 60-GHz radio-frequency carrier and second the intensity of a distributed feedback laser operating at 1300 nm. Properties of the multimode plastic optical fiber based on a perfluorinated material are exploited to transmit such signals. The overall system performance has been tested experimentally in a multihop configuration; bit-error-rate measurements are better than for transmission data rates up to 200 Mb/s.     

Spin Carrier Exchange Interactions in (Ga,Mn)N and (Zn,Co)O Wide Band Gap Diluted Magnetic Semiconductor Epilayers

(Ga,Mn)N and (Zn,Co)O wide band gap diluted magnetic semiconductor epilayers have been investigated by magneto-optical spectroscopy. In both cases, absorption bands observed below the energy gap allow us to study the nature of the valence and spin state of the incorporated magnetic element. Exchange interactions between magnetic ions and carriers can be observed by analyzing the magnetic circular dichroism in transmission or the exciton Zeeman splitting in reflection for (Zn,Co)O. A first estimation of the exchange integrals can be given for both materials.     

An Efficient Discretization of the Navier–Stokes Equations in an Axisymmetric Domain. Part 1: The Discrete Problem and its Numerical Analysis

Any solution of the Navier–Stokes equations in a three-dimensional axisymmetric domain admits a Fourier expansion with respect to the angular variable, and it can be noted that each Fourier coefficient satisfies a variational problem on the meridian domain, all problems being coupled due to the nonlinear convection term. We propose a discretization of these equations which combines Fourier truncation and finite element methods applied to each two-dimensional system. We perform the a priori and a posteriori analysis of this discretization.     

Thermomechanical analysis and modeling of the extrusion coating process

During the extrusion coating process, a polymer film is extruded through a flat die, stretched in air, and then coated on a substrate (steel sheet in our case) in a laminator consisting of a chill roll and a flexible pressure roll. The nip, i.e. the area formed by the contact between the pressure and the chill rolls, constitutes the heart of the extrusion coating process. Indeed, in this region, some of the most critical properties, such as adhesion, barrier properties, optical properties, are achieved or lost. In this article, we first present an experimental investigation of the coating step, which enables to characterize the leading thermomechanical phenomena. It is shown that there is no polymer macroscopic flow in the nip, but a local flow within the asperities of the steel substrate surface. This microscopic flow, at the interface between the film and the substrate, is slowed by strong cooling conditions in the nip. Several models are then proposed, giving access to the temperature profile through polymer thickness and substrate, the pressure distribution in the nip as well as the behavior of the polymer melt in the nip at the interface with the substrate. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Alternative expression of the Bloch wave group velocity in loss-less periodic media using the electromagnetic field energy

In periodic optical media, the group velocity is defined as the gradient with respect to wave-vector of the corresponding Bloch mode frequency dispersion curve, forming the photonic band structure. Instead of deducing it from the numerically computed photonic crystal band structure, the group velocity can be calculated directly from the integral of the Poynting vector over the crystal unit cell, the physical meaning of which is immediately perceivable. The related formula, which can be regarded as the application of Hellmann–Feynman theorem to electromagnetism, has been reported previously though without proof. We provide hereafter a full derivation of that formula starting from Maxwell’s equations and we discuss its usefulness in photonics.