The role of second‐order radial density gradient for helicon power absorption

To demonstrate the mysterious and still controversial mechanism of high ionization efficiency during helicon discharges, this work focuses particularly on the role of second‐order radial density gradient (SRDG) in helicon power absorption, both analytical and numerical. It was found that the positive or negative sign of SRDG and radial location of vanishing SRDG determine the radial profile of power absorption remarkably. First, by measuring SRDG at two radial locations (near plasma core and edge) where power absorption usually peaks, and varying it as a function of free parameter, we see that: (a) the power absorption from the antenna to plasma increases for positive SRDG and decreases for negative SRDG when viewed in the same x‐coordinate direction of SRDG and (b) the power absorption is maximized near the position where this local SRDG vanishes, consistent with the theory of radially localized helicon mode (B. N. Breizman and A. V. Arefiev, Phys. Rev. Lett., 84:3863, 2000). Second, by choosing the whole radial profiles of typical plasma distribution that have zero‐crossing SRDG, we find that the power absorption redistributes significantly when the location of vanishing SRDG moves radially outwards, and specifically when the radial locations of maximum power absorption and vanishing SRDG move in the same direction near the plasma core but noticeably in the opposite direction near the plasma edge. These findings are very interesting for helicon plasma applications that require certain power distribution or heat flux configuration, for example, material processing, which can be controlled by adjusting the radial profile of SRDG, especially the zero‐crossing SRDG.     

The critical effect of the surface density gradient on surface plasmon dispersion

An analytical expression is given for the linear dispersion coefficient of surface plasmons on metals and semiconductors. The influence of the surface density profile in the selvage region is included by a model which yields a critical width.     

Non-Maxwellian probability density function of fibers with lumped polarization mode dispersion elements

We give an analytical expression for the probability density function of the differential group delay for a concatenation of Maxwellian fiber sections and an arbitrary number of lumped elements with constant and isotropically oriented birefringence. When the contribution of the average squared of the constant birefringence elements is a significant fraction of the total, we show that the outage probability can be significantly overestimated if the probability density function of the differential group delay is approximated by a Maxwellian distribution.     

能够补偿二阶偏振模色散的三阶段偏振模色散补偿器

简要分析了偏振相关色散对光通信系统性能的影响,提出了一种三阶段高阶偏振模色散补偿方案,从理论上分析了它同时补偿偏振相关色散和偏振主态旋转的可能性,并提出了其可能存在的两种工作方式.通过数值模拟与两阶段补偿方案进行了性能比较,其偏振模色散容限比两阶段补偿提高约17%个比特周期 关键词： 光通信 光偏振 光纤色散     

Effect of cross-phase-modulation-induced polarization scattering on optical polarization mode dispersion compensation in wavelength-division-multiplexed systems

Interchannel cross-phase-modulation-induced polarization scattering (XPMIPS) and its effect on the performance of optical polarization mode dispersion (PMD) compensation in wavelength-division-multiplexed (WDM) systems are studied. The level of XPMIPS in long-haul WDM transmission systems is theoretically quantified, and its effect on optical PMD compensation is evaluated with numerical simulations. We show that in 10-Gbit/s ultra-long-haul dense WDM systems XPMIPS could reduce the PMD compensation efficiency by 50%, whereas for 40-Gbit/s systems the effect of XPMIPS is smaller.     

偏振模色散矢量的研究

研究了无损光纤的密勒矩阵,进而得出了偏振模色散矢量的解析表达式、主偏振态对应的斯托克斯矢量的解析表达式,以及高阶偏振模色散矢量的解析表达式.这些解析表达式是由光纤参数决定的.讨论了局部偏振模色散矢量与整体偏振模色散矢量的关系,讨论了利用偏振模色散矢量进行偏振模色散补偿的原理.引入了偏振模色散补偿元件的偏振模色散补偿矢量C,具体计算了正规的非圆光波导类的补偿元件的C.从理论上证明了仅仅利用一个正规的非圆光波导类的补偿元件,例如一根保偏光纤或是一个双折射晶体,是不能实现偏振模色散补偿 关键词： 偏振模色散 密勒矩阵 色散补偿 主偏振态斯托克斯矢量     

Measurement of polarization mode dispersion in single mode fibre

Polarization mode dispersion (PMD) in fibre seriously limits the high-capacity optical fibre communication system. The measurement of PMD was realized by three methods — wavelength scanning method, modified OTDR method and modified York S-38 dispersion meter method. Different types of fibres have been measured using the above three methods and the results have been found to be consistent. Finally, we also found that the measured results of longer non-polarization-maintaining fibre satisfied the Maxwellian probability density function and the results of polarization maintaining fibre were derived. Supported by The National Natural Science Foundations of P. R. China.     

Jones matrix of polarization mode dispersion

We describe how to calculate the Jones matrix transfer function of a fiber if its principal states of polarization and its differential group delay as functions of frequency are known. Using two counterexamples related to second-order polarization mode dispersion (PMD), we also show that a previous method used for the same purpose induces overestimation of second-order PMD effects by a factor of 2. Our new method is used to solve the problem for both counterexamples.     

Statistical properties of polarization mode dispersion

Polarization mode dispersion (PMD) is one of the effects which limit bit rates in optical communications systems. The statistics of PMD is complicated because it is multi-dimensional, however, many useful results have been obtained. Much work has been done, but the subject is not yet closed, as witnessed by the existence of this conference. In this talk I will review the way some statistical equations are treated. I will briefly discuss the methods of Ito and Lax, and their application to the PMD problem.     

Performance of conformal guided mode resonance filters

Guided mode resonance (GMR) filters are highly functional micro-optics capable of narrowband spectral filtering. GMR devices have previously been demonstrated on flat substrates using a wide range of materials and configurations. In this Letter, we apply a soft lithographic technique followed by the deposition of dielectric layers to generate GMR filters on a concave lens surface. Resonances of the resulting conformal GMR filters are experimentally measured and characterized, and the results are compared to the performance of similar GMR filters fabricated on flat surfaces.     

Excellent polarization-independent reflector based on guided mode resonance effect

A broad band polarization-independent reflector working in the telecommunication C+L band is proposed using the guided mode resonance effect of a periodic surface relief element deposited by a layer of silicon medium. It is shown that this structure can provide high reflection (R>99.5%) and wide angular bandwidth (θ≈20°, R>98%) for both TE and TM polarizations over a wide spectrum band 1.5 μm～1.6 μm. Furthermore, it is found by rigorous coupled wave analysis that the polarization-independent reflector proposed here is tolerant of a deviation of grating thickness, which makes it very easy to fabricate in experiments.     

Simplified mode analysis of guided mode resonance gratings with asymmetric coatings

A simplified modal method to explain the resonance phenomenon in guided mode resonance(GMR) gratings with asymmetric coatings is presented.The resonance observed is due to the interaction of two propagation modes inside the grating.The reflectivity spectra and electric field distributions calculated from the simplified modal method are compared using rigorous coupled-wave analysis(RCWA).The influences of high-order evanescent modes on the resonance peak are analyzed.A matrix Fabry-Perot(FP) resonance condition is developed to evaluate the resonance wavelength.An explanation for the resonance phenomenon observed based on the FP resonance phase condition is also proposed and demonstrated.The simplified method provides clear physical insights into GMR gratings that are useful for the analysis of a variety of other resonance gratings.     

Theory of density functional gradient series

It is shown how a reformulation of a density functional gradient expression optimises the convergence of this series.     

Interaction of nonlinearity and polarization mode dispersion

The derivation of the coupled nonlinear Schrödinger equation and the Manakov-PMD equation is reviewed. It is shown that the usual scalar nonlinear Schrödinger equation can be derived from the Manakov-PMD equation when polarization mode dispersion is negligible and the signal is initially in a single polarization state as a function of time. Applications of the Manakov-PMD equation to studies of the interaction of the Kerr nonlinearity with polarization mode dispersion are then discussed.     

偏振模色散模拟器的特性

通过对微分群时延差(DGD)统计特性和偏振模色散(PMD)矢量自相关函数的数值模拟，分析比较了目前常用的三种PMD模拟器的性能. 结果表明：在DGD分布方面，由DGD发生器构成的模拟器，一个DGD发生器就可与实际光纤PMD的统计特性相符合，而由保偏光纤和可旋转的连接器构成的模拟器则至少需要15段. 在自相关函数方面，基于保偏光纤的模拟器取决于各段光纤的延时量，而基于DGD发生器的模拟器在中心频带外的自相关值很平稳，可视为常数. 关键词： 光纤通信 偏振模色散 偏振模色散模拟器 自相关函数     

Statistics of the polarization mode dispersion dynamics

We characterize the joint two-time statistics of the polarization-mode dispersion (PMD) vector. Good agreement with experimental PMD measurements taken on an installed system is achieved. The results can be used to obtain the temporal evolution of the average penalty of a system close to an outage condition.     

Peculiarities of the helicon mode propagation with m < 0 in radially nonuniform plasma cylinder

The peculiarities of the helicon mode propagation with m < 0 along plasma cylinder with radial density gradient are analysed. It is shown that the modes with m < 0 can propagate near cylinder axis region where the effects of density gradient are not important.     

Broadband non-polarizing beam splitter based on guided mode resonance effect

A broadband non-polarizing beam splitter (NPBS) operating in the telecommunication C+L band is designed by using the guided mode resonance effect of periodic silicon-on-insulator (SOI) elements. It is shown that this double layer SOI structure can provide ～50/50 beam ratio with the maximum divergences between reflection and transmission being less than 8% over the spectrum of 1.4 μm～1.7 μm and 1% in the telecommunication band for both TE and TM polarizations. The physical basis of this broadband non-polarizing property is on the simultaneous excitation of the TE and TM strong modulation waveguide modes near the designed spectrum band. Meanwhile, the electric field distributions for both TE and TM polarizations verify the resonant origin of spectrum in the periodic SOI structure. Furthermore, it is demonstrated with our calculations that the beam splitter proposed here is tolerant to the deviations of incident angle and structure parameters, which make it very easy to be fabricated with current IC technology.     

圆管超声导波频散与多模态特性研究*

超声导波检测技术作为一种新兴的无损检测技术广泛应用于圆管类结构。为选择合适于不同缺陷检测的导波模态,推导分析了圆管导波传播的运动方程和频散方程;利用数值计算的方法得到了超声导波在圆管中传播的频散曲线和各模态沿壁厚方向的位移分布图,分析得出各个模态对不同缺陷的敏感程度;以一种特定的圆管为例,建立圆管缺陷有限元模型,对不同类型圆管缺陷对导波传播特性的影响进行仿真计算。结果表明,纵向模态对周向缺陷比较敏感,而扭转模态则对轴向缺陷更敏感,仿真结果与理论分析结果相吻合,为圆管缺陷检测的超声导波模态选择提供了理论依据。     

Effect of refractive index of environment medium on electromagnetic mode density in photonic band gaps

The purpose of this work is to analyze the effect of the environmental medium on the density of mode (DOM) in a 1-D photonic crystal. The results show that for a symmetric environment, the DOM changes non-monotonously with an increase in the refractive index of the environment medium, while for an asymmetric environment, the DOM increases monotonously with an increase of the refractive index of the substrate. It is found that low DOM at midgap and high DOM at the band edge can be achieved simultaneously only when a photonic crystal works in an environment where the input medium and the substrate have the same refractive indices. The effect of the refractive index on the surrounding material on the band edge laser is also discussed. PACS 42.70.Qs; 71.20.Tx