Effect of intrapulse Raman scattering on broadband amplitude noise of supercontinuum generated in fiber normal dispersion region

Based on the generalized stochastic nonlinear Schr?dinger equation, the effect of intrapulse Raman scattering (IRS) on broadband amplitude noise of supercontinuum (SC) generated in the normal dispersion regime is investigated numerically. The results show that, in the normal dispersion regime, where the IRS contributes less to the bandwidth of the SC spectrum, the broadband amplitude noise of SC is amplified significantly in the process of SC generation because of the existence of IRS effect. Using fiber with an optimal negative dispersion slope, the IRS effect can be suppressed, and thus the SC amplitude noise is reduced without spectral bandwidth loss.     

Supercontinuum generation in quantum wells facilitated by electromagnetically induced transparency

In this paper, employing numerical simulation, we examine the possibility of generation of optical supercontinuum (SC) in a multiple quantum well (MQW) system facilitated by electromagnetically induced transparency. Within the transparency window created by a control laser beam in a MQW, another probe pulse experiences negligible loss and large optical non-linearity that has been exploited to obtain the optical SC. With 1.0 pico-second ‘sech’ probe pulses of 500 W peak power at wavelength 739.7 nm, the numerically simulated SC spectrum at the end of the 9.377 μm long MQW extends from 550 to 1000 nm. The spectrum is asymmetric, contains large number of oscillations which is attributed to the nonlinearity induced self-phase modulation and modulation instability. This investigation may lead to the fabrication of on-chip SC sources that can be easily integrated with other semiconductor devices.     

Influence of acoustic waves on supercontinuum generation in photonic crystal fibers

In this work, the influence of applying acoustic frequencies to photonic crystal fibers (PCF) on the supercontinuum (SC) generation is presented. We will show numerically the strong influence of coupling modes in PCF in the latest stage of SC and simulations of different scenarios of phase math condition between the modes.     

Combination of highly nonlinear fiber, an optical bandpass filter, and a Fabry-Perot filter to improve the signal-to-noise ratio of a supercontinuum continuous-wave optical source

We present a theoretical study of a supercontinuum (SC) continuous-wave (cw) optical source generation in highly nonlinear fiber and its noise properties through numerical simulations based on the nonlinear Schr?dinger equation. Fluctuations of pump pulses generate substructures between the longitudinal modes that result in the generation of white noise and then in degradation of coherence and in a decrease of the modulation depths and the signal-to-noise ratio (SNR). A scheme for improvement of the SNR of a multiwavelength cw optical source based on a SC by use of the combination of a highly nonlinear fiber (HNLF), an optical bandpass filter, and a Fabry-Perot (FP) filter is presented. Numerical simulations show that the improvement in modulation depth is relative to the HNLF's length, the 3-dB bandwidth of the optical bandpass filter, and the reflection ratio of the FP filter and that the average improvement in modulation depth is 13.7 dB under specified conditions.     

Supercontinuum and rogue soliton generation by induced modulational instability in photonic crystal fibre

Abstract

We present an approach that enables active control of supercontinuum (SC) and rogue soliton (RS) generation through the modulation of a 500 fs input pulse by numerical simulations. The induced modulational instability contributes to the initial comb-like SC generation, which is fundamentally different from SC initiated by high-order soliton fission. The output spectrum shows great dependence on modulation frequencies and depths. It is interesting that we can manipulate the RS generation by adjusting the modulation parameters. And we also demonstrate the conditions which can be beneficial to RS generation: (i) very weak or large values of modulation depth; (ii) seeding in the vicinity of the peak of the modulational instability gain spectrum. Although RS degrades the smoothness of the SC, it is of great significance in the generation of tailored SC.     

Tilting tolerance analysis of a broadband polarization-preserving beam displacer

We numerically investigated the performance of an achromatic polarization-preserving beam displacer that was proposed by Galvez [Opt. Lett.26,971(2001)]. First, the four-prism configuration of the Galvez scheme is verified by simulation. We examined the extension of wavelength beyond visible light by considering the corresponding power loss. The degree of polarization is also considered. The tolerance of tilts of reflecting surfaces is comprehensively discussed. It is shown that the second reflector of a four-prism system is the most critical component. Performance of various materials, including plastics, is evaluated. We explain a simplified implementation based on two prisms (the classic Porro configuration), which also improves material performance.     

单晶高温合金发展现状EI

从８０年代初第一代单晶高温合金研制成功以来，单晶合金的发展甚为迅速，第二代、第三代单晶合金相继出现和应用，为航空发动机和地面燃气轮机的性能大幅度提高作出了重大贡献。单晶合金及其工艺的发展具有一系列重要特点。其应用范围日益扩大。预计今后相当长一段时期，单晶高温合金仍将是先进燃气涡轮发动机最主要的叶片材料。我国在单晶合金及工艺研究方面已取得显著成绩，但是仍落后于当前国际先进水平。     

Studies in an optical millimeter-wave generation scheme via two parallel dual-parallel Mach–Zehnder modulators

A novel filterless optical millimeter-wave generation scheme via two parallel dual-parallel Mach–Zehnder modulators (MZMs) is proposed. Theoretical analysis suggests that it can be used for the generation of millimeter-wave signal with octupling or 16-tupling of the local oscillator. An 80?GHz millimeter-wave is generated by octupling of a 10?GHz RF oscillator, or 16-tupling of a 5?GHz RF oscillator. Several influence factors on the performance of the optical sideband suppression ratio (OSSR) and the radio frequency spurious suppression ratio (RFSSR) are numerically studied. Simulation results show that the generated millimeter-wave can keep good performance, especially for octupling millimeter-wave generation; its performance is stable and insensitive to the extinction ratio of MZMs and the DC bias drift.     

Two Modified Semicircle Control Charts for Detecting Process Improvement

A semicircle control chart can be used in detecting both increases and decreases in the mean and/or variance. In this paper, we propose two modified semicircle charts for detecting a reduction in the process variance, a.k.a. process improvement. Each of these modified semicircle charts, namely, SC1 and SC2 has two limits, defined by the inner and outer semicircles. A process improvement is detected by the SC1 scheme if a point is plotted inside the smallest semicircle, or if two successive points are plotted between the inner and outer semicircles and by the SC2 scheme if a point plots inside the smallest semicircle or if two of three successive points plot between the inner and outer semicircles. It will be shown that the two modified semicircle charts have superior average run length (ARL) performances to the basic semicircle chart in the detection of process improvement. The ARL study is conducted by means of a simulation.     

Series compensation method to mitigate harmonics and voltage sags and swells

The use of a series compensator (SC) to improve power quality is investigated. The role of the compensator is not only to mitigate the effects of voltage sag and swell, but also to control the level of harmonic distortions in the network. This is accomplished through extension of the voltage injection scheme of the SC by the incorporation of load current feedback and an external inductive filter. The compensation process is accompanied by an exchange of energy between the SC and the external network. Through a phase adjustment technique, it is shown that the voltage quality across the terminals of the protected load can be controlled. Simulation studies, supported by laboratory experiments, show that the resulting series compensation scheme is effective in improving the supply quality of the power system.     

Low cycle fatigue modeling for nickel-based single crystal superalloy

The low cycle fatigue (LCF) characteristics of nickel-based single crystal (SC) superalloy have been experimentally and numerically investigated. The effects of crystallographic orientation, load ratio and stress concentration are studied. In order to model the effect of crystallographic orientation, a new orientation factor, which is relevant to the yield strength, is constructed. On the other hand, a new asymmetrical loading factor is introduced to describe the effect of load ratio. The LCF model for SC superalloy smooth specimen is established with these new damage parameters. The effect of the strain gradient on the LCF life of SC superalloy is further studied, which is applied to the evaluation of the LCF life of SC superalloy notched specimen. The LCF model proposed is validated by the experimental data of SC superalloy DD3 and PWA1480.     

Kerma rate effects on thermoluminescent response of CVD diamond

The thermoluminescence (TL) response of chemical vapour deposition diamond is studied after X-irradiation (45 kV) at room temperature for various air kerma rates ranging from 0.7 to 100 Gy.min(-1). For a given air kerma, the TL signal as a function of air kerma rate exhibits large variations and is higher for low air kerma rates than for higher ones. In order to explain these results, the simplest energy-level scheme has been considered, that is, with only one electron trap and one recombination centre. Kinetic equations are numerically solved. Calculations are made for various electron-hole generation rates and show that the trap filling as a function of electron-hole generation rate follows, actually, the same evolution as the one of experimental TL response. The kerma rate effect on TL response is explained by the competitivity between the recombination and the trapping processes during irradiation.     

Magnetohydrodynamic natural convection flow on a sphere with uniform heat flux in presence of heat generation

Summary Magnetohydrodynamic natural convection boundary layer flow on a sphere with uniform heat flux in presence of heat generation has been investigated in this paper. The governing boundary layer equations are transformed into a non-dimensional form and the resulting nonlinear system of partial differential equations is then solved numerically by two distinct efficient methods, namely (i) implicit finite difference method together with the Keller box scheme and (ii) perturbation or series solution technique. The results of the surface shear stress in terms of local skin friction and the rate of heat transfer in terms of local Nusselt number, velocity distribution as well as temperature distribution are shown graphically for a selection of parameter sets consisting of the heat generation parameter and the magnetic parameter.     

Magnetic Field Analysis of Inset and Surface-Mounted Permanent-Magnet Synchronous Motors Using Schwarz–Christoffel Transformation

In this paper, we apply an original numerical Schwarz–Christoffel (SC) transformation to analyze magnetic field originating from permanent magnets and the armature winding currents in a slotted air gap of an inset permanent-magnet synchronous motor. We obtained the solution of the SC integral numerically using Matlab SC Toolbox. We used this field solution to calculate both cogging torque and electromagnetic torque by integrating the Maxwell stress tensor inside the air gap. The case without inter-polar piece, which is equivalent to a surface-mounted permanent-magnet motor, is also treated. The accuracy of the developed method is verified by comparing its results with those obtained from the developed numerical finite-element models.      

The Meissner-Ochsenfeld effect as a possible tool to control anisotropy of thermal conductivity and pinning strength of type II superconductors

This paper proposes the Meissner-Ochsenfeld effect as a possible tool for quality control of type II superconductors (SC). Visual or optical inspection of the levitation process allows rough determination of the anisotropy of thermal conductivity and of the pinning strength of type II SC material, in a materials quality control. An assembly of permanent (e.g. NdFeB) or electromagnets and a flat cryostat allowing visual or optical inspection would be required. The method is demonstrated by numerically simulating the field cooling process of a superconducting cylindrical pellet and of a coated conductor.     

Efficient 550-600-nm tunable laser based on noncritically phase-matched frequency doubling of room-temperature LiF:F2- in lithium triborate

We report on efficient conversion of a 1064-nm Nd:YAG laser to tunable visible light. The conversion scheme uses noncritically phase-matched second-harmonic generation of a pulsed Nd:YAG-pumped LiF:F2- laser in lithium triborate. Optimization yields 42% LiF:F2- laser efficiency and 56% frequency-doubling efficiency, providing >20% conversion from 1064 nm to broadly tunable visible output. A dramatic sensitivity of laser efficiency to pump pulse duration is recorded, with a fundamental efficiency improvement of over 30-fold measured for an increase in pump pulse duration from 5 to 34 ns.     

Optical properties of the scales of Morpho rhetenor butterflies: theoretical and experimental investigation of the back-scattering of light in the visible spectrum.

A study of the optical properties of the largely periodic microstructure occurring on the wings of the iridescent tropical butterfly Morpho rhetenor and responsible for its structural colouration is reported. An extensive measurement of the back-scattering of visible light from butterfly scales was performed for various angles of incidence. Efficient low-pass filter behaviour was observed for all angles of incidence and polarizations, with near-complete transmission at wavelengths above the threshold of 550 nm. The angular spread of the back-scattered light was found to be organized in lobes with total extinction of the specular reflection for all conditions of incidence. Retro-reflector behaviour was also observed for angles of incidence of 30 degrees and above. Additionally, the role of periodic geometrical features found in the microstructure for the generation of its spectral response was analysed theoretically. Using finite-difference time-domain and near-field to far-field transformation techniques, the back-scattering of visible light by models was computed numerically and the relevance of geometrical features for the production of structural colour and diffraction was demonstrated.     

Optimal control of high harmonics for the generation of double attosecond pulses by using a chirped laser pulse

An efficient scheme for the optimization of ultrashort femtosecond pulse shapes interacting with an atom to control high harmonics spectrum and double attosecond pulse generation is presented. The time-dependent Schrödinger equation of one-dimensional hydrogen atom is solved numerically to obtain electric field emission. The genetic algorithm optimization method is used to control the phase and amplitude of ultrashort excitation laser pulses to generate the desired attosecond-shaped pulses. An appropriate cost function is introduced for genetic algorithm optimization of double attosecond pulse generation. It is shown that the relative intensity of two generated pulses, their delay time and duration can be controlled in this approach. Finally, the parameters of the optimized emitted attosecond pulse are compared with those of desired pulses, and the underlying physical mechanisms are discussed in detail.     

Methodological approaches to supply chain design1

This paper reviews methodological approaches to the design (or redesign) of the supply chain (SC), including comprehensive approaches (proposals concerning the entire process of designing the SC) and those that deal with four specific aspects of the process (definition of the SC objectives, reverse SC, finance, and generation and use of scenarios) that have a decisive influence on the whole design of the SC. The comprehensive approaches include those based on typologies of products, markets and SCs and those that propose a succession of the stages to follow through the design process. The discussion shows that the use of typologies is not adequate to face SC design and that the methods proposing a succession of stages may suit, provided that they are developed and presented in a manner appropriate to their use for practitioners. The discussion leads also to suggest several research lines.     

Characterization of inks and ink application for ink-jet printing: model and simulation

Ink-jet printing quality is determined primarily by, among other factors, the printing engine and its inks. The printing engine controls the process of ink application and the scheme of ink mixing for th e generation of secondary and tertiary colors. The inks selectively absorb different wavelengths from the illumination and result in the visible color output. Therefore characterizations of the output print in terms of ink distribution and volume, the scheme of ink mixing, light absorption, and light scattering are of essential importance in controlling and understanding the quality of the color reproduction. I present a method to characterize the ink volume and the properties of the ink by means of spectral reflectance measurements and simulations. The simulations are based on the Kubelka-Munk theory, whose applicability to ink-jet printing is also discussed.