Four-wave mixing analysis in WDM optical communication systems with higher-order dispersion

Four-wave mixing (FWM) is one of the major limiting factors in WDM optical fiber communication systems. In this paper, we analyze the individual and combined effect of second-, third-, fourth- and fifth-order dispersion parameters on FWM at different input channel powers and core effective areas, which have not been calculated earlier. FWM power versus channel power graphs for individual and combined effects of dispersion parameters have been presented, and it has been observed that FWM reduces for combined effect of dispersion parameter.     

Designing a graded index depressed clad non-zero dispersion shifted optical fiber for wide band transmission system

Non-zero dispersion shifted fibers (NZ-DSFs) find extensive use in wavelength division multiplexed (WDM) system as it reduces the non-linear effects like four-wave mixing (FWM) generation. A depressed clad graded index fiber with a central dip in the refractive index profile, as well as without dip, has been modeled to perform as an NZ-DSF using the spot size optimization technique. The performance characteristics of the proposed NZ-DSF have been studied by changing different fiber parameters; such as inner core radius (a), relative refractive index differences (Δ⁺), normalized end position of depressed clad (C), depression parameter (ρ), etc. for a given value of Petermann-2 spot size . By suitably adjusting the fiber parameters, the effective core areas (A_eff) as simulated here are very large (80 μm²) so that the effect of non-linearities upon them can be minimized. These NZ-DSFs have also been optimized for WDM transmission system. The dispersion slopes of the proposed fibers with and without dip have been estimated which are comparable with the reported results.     

A two-step strategy for numerical simulation of radiative transfer with anisotropic scattering and reflection

This article presents a two-step procedure for the computation of radiative heat transfer with anisotropic scattering and reflection. It is based on a concept that the coincident processes of absorption and scattering/reflection can be separated factitiously. All medium elements and wall surfaces are supposed to be pure-absorbing when receiving incident radiation. Afterwards they emit the scattered/reflected radiations. The absorption of both the initial and the secondary radiations can be assessed by the direct exchange area. It is needed to repeat the processes for a few times until the radiations are substantially absorbed. For anisotropic scattering/reflection, a vector summation obtains the directional distribution of emissive power. The method is validated by several benchmark computations in terms of emissive power and heat transfer coefficients. It is shown that the method gives more accurate solution than the isotropic scaling for the heat transfer in anisotropically scattering media.     

Thermal stability of the structural features in the superhydrophobic boehmite films on austenitic stainless steels

Boehmite thin film with 50–100 nm surface flake structure has been synthesized on AISI 316 type austenitic stainless steel by immersing boehmite gel film into boiling water. When further coated with hydrolyzed (heptadecafluoro-1,1,2,2-tetrahydrodecyl) trimethoxysilane (FAS), the boehmite film becomes superhydrophobic with a contact angle for water of 152°. The superhydrophobic property results from both the nanoscale surface flake structure and the low surface energy of the FAS top layer. The topography of such film was revealed by atomic force microscope (AFM) and a set of roughness parameters of such film was discussed. The degradation of superhydrophobicity of the surface was studied as a function of the heat-treatment temperatures. Below 600 °C, the surface remained to be superhydrophobic with the FAS top layer. Above 700 °C, the surface was not superhydrophobic anymore due to a gradual loss in surface roughness which was revealed by field emission scanning electron microscope (FESEM). A phase change from boehmite to γ-Al₂O₃ occurred during the heat-treatments from 700 to 900 °C which was studied by the selected area electron diffraction (SAED) patterns from the transmission electron microscope (TEM) measurement.     

Low temperature ageing of silicas Gasil-I and TK800

Gasil-I (a mesoporous silica) and TK800 (a non-porous pyrogenic silica) were investigated in the early 1970s as standard reference materials. Since then the specific surface areas of both silicas have decreased to ∼85% of their initial values, suggesting that the surface character and the ageing mechanism may be the same for both. Comparisons of the shapes of nitrogen-adsorption isotherms, confirmed by comparisons of the shape ratios for Gasil-I and TK800, indicate that Gasil-I has greater microbore character and a higher absorption at p/p₀ > 0.5 than TK800 and that the isotherm shapes have changed little since 1974. The specific volume of Gasil-I has remained nearly constant during the ageing period but the pore size distribution (PSD) has shifted markedly to higher values.Electron micrographs show that low (room) temperature gas-solid ageing results in similar enlargement at the point of contact between attached secondary particles as that which occurs in hydrothermal ageing. In the gas-solid case, this change, which accounts for the decrease in overall surface area, is attributed to the surface transport of silica material in the presence of near monolayer quantities of adsorbed water. Ageing in this manner is geometry-limited so that the rate of ageing is expected to approach zero, resulting in time-stable silicas.     

Ultra‐large effective‐area,higher‐order mode fibers: a new strategy for high‐power lasers

This paper describes the physics and properties of a novel optical fiber that would be attractive for building high‐power fiber lasers and amplifiers. Instead of propagating light in the fundamental, Gaussian‐shaped mode, we describe a fiber in which the signal is forced to travel in a single, desired higher order mode (HOM). This provides for several advantages over the conventional approach, ranging from significantly higher ability to scale mode areas (and hence laser powers) to managing dispersion for ultra‐short pulses – a capability that is practically nonexistent in conventional fibers. Particularly interesting is the fact that this approach challenges conventional wisdom, and demonstrates that for applications requiring meter‐length fibers (as in high‐power lasers), signal stability actually increases with mode order. Using this approach, we demonstrate mode areas exceeding 3200 μm², and propagate signals with negligible mode distortions over up to 50‐meter lengths. We describe several pulse propagation experiments in which we test the nonlinear response of this fiber platform, ranging from managing dispersive effects in femtosecond pulse systems, to reducing Brillouin scattering impairments in systems operating with the nanosecond pulses.     

大面阵数码相机快门驱动机构的设计分析与改进

设计了一套用于大面阵数码相机的全电控快门驱动机构。连杆机构驱动幕帘快门上弦,杠杆机构驱动快门释放。对上弦连杆机构的设计进行了较详细的分析和计算,并对机构在调试中出现的一些问题进行了分析和改进。     

强流电子束泵浦百焦耳级氟化氪激光

本文介绍中国原子能科学研究院建造的强流电子束泵浦的百焦耳级氟化氪激光装置的主要性能,重点介绍脉冲功率技术和激光振荡器的一些关键技术。     

停车场规划的分片凸规划-建模、算法及应用

本研究停车场选址问题。本抓住主要矛盾，建立实用停车场选址的分片凸规划模型。设计往复调整、下降迭代相结合的算法。并在常州市交通管理规划应用中取得了良好的效果。     

A partial surface area measurement method for multicomponent catalysts and adsorbents

A new universal method for partial surface area measurements (PSAM) of multicomponent catalysts and adsorbents is proposed. The method is based on the dependence of specific adsorption on the surface area composition. It was realized in fast gas-chromatographic regime. The effectiveness of this method was shown for SiO₂-carbon mechanical mixtures withn-butane used as an adsorbate.