Statistics of the DGD in PMD emulators

We give the statistics of the differential group delay at the output of a polarization-mode dispersion emulator made of a chain of fiber sections with constant birefringence, fixed and arbitrarily selected lengths, and randomly oriented polarization controllers in between.     

Four-wave mixing in traveling-wave semiconductor amplifiers

The traveling-wave equations of four-wave mixing in semiconductor amplifiers are solved analytically including saturation of the amplifier. Excellent agreement is obtained with numerical solutions of the traveling-wave equations. The analytical model is used to analyze a highly nondegenerate four-wave mixing experiment in a bulk semiconductor amplifier     

Small-signal theory of wavelength converters based on cross-gain modulation in semiconductor optical amplifiers

We give the exact closed form solution of the coupled-mode equations describing frequency converters based on cross-gain modulation in semiconductor optical amplifiers. We show that the frequency response of the converter is strongly affected by the waveguide internal loss.     

Efficiency and noise performance of wavelength converters based onFWM in semiconductor optical amplifiers

All optical frequency converters are key devices for new-conception optical networks. A theoretical model is presented to evaluate performances of frequencies converters based on highly nondegenerate four-wave mixing (FWM) in semiconductor amplifiers. Conversion efficiency and noise performances are evaluated in generic saturation conditions and compared with experimental results     

Analysis of the <Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">α</Emphasis> transformation in a C-Mn steel by phase-field modeling

This article deals with the austenite (γ) decomposition to ferrite (α) during cooling of a 0.10 wt pct C-0.49 wt pct Mn steel. A phase-field model is used to simulate this transformation. The model provides qualitative information on the microstructure that develops on cooling and quantitative data on both the ferrite fraction formed and the carbon concentration profile in the remaining austenite. The initial austenitic microstructure and the ferrite nucleation data, derived by metallographic examination and dilatometry, are set as input data of the model. The interface mobility is used as a fitting parameter to optimize the agreement between the simulated and experimental ferrite-fraction curve derived by dilatometry. A good agreement between the simulated α-γ microstructure and the actual α-pearlite microstructure observed after cooling is obtained. The derived carbon distribution in austenite during transformation provides comprehension of the nature of the transformation with respect to the interface-controlled or diffusion-controlled mode. It is found that, at the initial stage, the transformation is predominantly interface-controlled, but, gradually, a shift toward diffusion control takes place to a degree that depends on cooling rate.     

A Theory of Polarization-Mode Dispersion of Spun Fibers

We give a compact theory of the polarization-mode dispersion (PMD) in spun fiber. For periodically spun fibers, the theory shows that the asymptotic behavior of the PMD can be predicted by a simple procedure from the two-dimensional Fourier transform of the birefringence correlation function.     

Hydrogen enhanced fatigue in full scale metallic vessel tests – Results from the MATHRYCE project

This study investigates the fatigue life of CrMo pressure vessels for hydrogen storage by hydraulic and hydrogen pressure cycle tests. Two different sized cylinders have been tested; 35 L inner volume and 28 MPa working pressure (WP) and 198 L volume and 41 MPa WP. On the inner surface of the cylinders U-shaped notches of different depths were machined by electro discharge machining technique. The initial notch sizes were designed based on a two stage fatigue predictive model based on fracture mechanics to develop through wall cracks in the deepest notches after about 50,000 hydraulic cycles together with crack propagation of the intermediate notches and crack initiation in the smallest. The cylinders were cycled between the nominal pressure of 2 MPa and the WP until leak before break (LBB). Strain gauges were placed at the external surface of the cylinders in correspondence of the internally machined notches. On the notches which developed through wall, the strain showed a progressive decrease followed by an increase of the hoop strain during the final stage of crack propagation until LBB failure. Hydrogen effect was clearly identified by the reduction in the number of cycles to failure comparing tests in hydrogen and in oil. Subsequent failure analysis at the end of each test revealed a typical trans-granular fatigue crack surface morphology (with fatigue striations) for tests in oil, while quasi cleavage and intergranular fracture appearance were found for hydrogen tests.     

Phase field simulation of the carbon redistribution during the quenching and partitioning process in a low-carbon steel

Phase-field modelling is used to simulate the quenching and partitioning process in a low-carbon transformation-induced plasticity (TRIP) steel, in order to understand the carbon redistribution in the microstructure during the heat treatment. The simulations show that, depending on local characteristics of the microstructure, including phase distributions and carbon-concentration gradients, different features in the carbon evolution during the partitioning step occur that are physically and practically relevant, but are not accessible for experimental observation. The overall carbon partitioning from martensite to austenite occurs not only by direct diffusion from martensite to austenite, but also through the bulk ferrite grains. The simulations also show interface migration driven by the free-energy difference between austenite and martensite, which affects the fractions of phases and the dimensions of the austenite grains. The carbon content of individual austenite, martensite and ferrite grains as well as average values are analysed, showing that the carbon concentration within the austenite grains is strongly inhomogeneous at short partitioning times, which contributes to a variable mechanical stability of individual austenite grains, affecting the occurrence of TRIP.     

System impact of intra-channel nonlinear effects in highlydispersed optical pulse transmission

We provide accurate analytical estimates of timing- and amplitude-jitter caused by nonlinear pulse interaction in systems based on highly dispersed optical pulses, both for coherent and noncoherent pulse streams. We show that the system penalties reduce monotonically with pulsewidth and with increasing fiber dispersion. We demonstrate that proper dispersion pre-compensation can result in a significant reduction of the nonlinear inpairments and provide analytical tools for obtaining the optimal pre-compensation parameters