共查询到18条相似文献,搜索用时 155 毫秒
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反常色散介质“超光速”现象研究的新进展 总被引:2,自引:0,他引:2
文章介绍了王力军等人的光脉冲在反常色散介质传播实验的测量结果,说明了实验测量的不完全性,因而它不能在是否超光速的问题的答案,文章还介绍了近一年来相应的理论研究工作,文章作者依据物理概念和理论研究结果论证了该实验所得的负群速度本身并不超光速;如果把负群速度看成是某种能量的传播那私超光速出现在负群速度开始时间间,因而它是超距作用,违反能量守恒或动量守恒,因此,负群速度只是表观速度,能流的研究结果也证明了这一点。这就是说,该实验并没有观察 到超观察到超光速传播。 相似文献
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《中国光学与应用光学文摘》2007,(4)
O432007043016超光速群速度与信息传输的有效速度=Superluminalgroup velocity and effective velocity of information transfer[刊,中]/郭奇志(上海大学物理系.上海(200444)),谭维翰//光学学报.?2007,27(2).?344-349研究了反常色散介质中脉冲形变对超光速群速度的影响,发现即 相似文献
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研究了反常色散介质中脉冲形变对超光速群速度的影响,发现即使光脉冲完全不产生形变群速度仍会超过真空中的光速。但波包的群速度并不等同于信号的传输速度,采用信息论方法,定义了信号的有效传输速度,并用于解释WKD(Wang,Kuzmich,Dogariu)实验。通过计算入射光与出射光信号所携带的信息量,发现由于光的波动衍射及光子散粒噪声的影响,出射光所携带的信息量会损失,使得光信号的有效传播速度不会超过真空中的光速。 相似文献
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通过在能量较高、考虑非线性时,求解光纤光栅非线性耦合模方程连续波条件下的解,得到光纤光栅失谐量δ与光脉冲传播常量q的非线性色散关系和光栅致群速度色散系数βg2与δ的关系.用MATLAB绘图,得到非线性参量γ和光脉冲能量P0的乘积γP0对色散和βg2的影响.结果表明:随着βg2的增加,非线性色散曲线的上、下两支向δ的负值区移动,当超过某一临界值时,曲线上支开始形成环,这时光纤光栅引起的群速度色散中的反常色散区消失,全部变成正常色散. 相似文献
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光子晶体中缺陷的色散导致的群速度降低 总被引:8,自引:4,他引:4
利用传输矩阵方法计算了包含色散媒质缺陷的一维光子晶体的复透射系数,其中色散媒质用洛仑兹振子模型描述。计算了由复透射系数定义的等效复折射率并由此研究了频谱位于缺陷模频率附近的光脉冲的群速度。结果发现,由于缺陷模附近的透射谱敏感地依赖于缺陷层的光学厚度,而缺陷层的色散使缺陷层光学厚度随频率变化而改变,从而使包含缺陷的光子晶体的等效色散性质明显地依赖于缺陷的色散行为。由于光脉冲是由多种频率成分的单色场迭加构成的,透射脉冲由各单色场透射后重新迭加构成,因此波包的传播由介质的等效色散性质决定。与包含无色散缺陷的光子晶体相比,缺陷的色散可导致极慢的群速度。通过改变振子强度,群速度可从极慢光速转变为超光速(superluminal)。 相似文献
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在耦合模理论的基础上,分析了线性周期结构的色散关系,给出了一维无限长的克尔类非线性介质周期结构中的慢布拉格类孤子解。并且指出,增加脉冲能量会导致群速度色散效应增强,在非线性作用下,禁带宽度会变小,波的频率也会发生偏移,其偏移量主要取决于失谐因子、传播速度、波振幅强度以及非线性系数等参量。 相似文献
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We report a low-loss photonic crystal slab waveguide formed by deforming the innermost circle air holes in the conventional photonic crystal slab waveguide into elliptical ones. We obtain the photonic bands and group index of guided modes in this photonic crystal waveguide by guided-mode expansion method and investigate the dependence of photonic bands and group index of guided modes on the parameters of the innermost elliptical air holes. The group velocity and group velocity dispersion of this waveguide strongly depend on the innermost elliptical air holes. Photonic crystal slab waveguide with the optimum innermost elliptical air holes possesses a wider single mode region below the light line, in which light can easily propagate without intrinsic loss. At the same time, the guided mode supported by this waveguide has nearly constant group velocity and vanishing group velocity dispersion in a 3-5 nm bandwidth. 相似文献
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研究了单光子晶体界面介质波导中的慢光效应.芯层-空气层界面的全内反射效应以及光子晶体基底的禁带效应共同形成了对光场能量的横向约束.用基于超元胞的平面波展开法计算得到了导模色散曲线,并据此对其色散、群速以及群速色散性质做了详尽分析.由于利用了色散曲线慢光区域内拐点附近低群速色散的部分,该单光子晶体界面介质波导具有良好的慢光特性.对两个不同导模计算得到的平均群速分别为c/98和c/376,可用相对频带宽度分别达到2.1×10-3和4.1×10-4.另外,该慢光结构可以侧向耦合的方式克服光子晶体慢光波导耦合困难的缺点. 相似文献
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The energy input and frequency shift of geodesic acoustic modes (GAMs) due to turbulence in tokamak edge plasmas are investigated in numerical two-fluid turbulence studies. Surprisingly, the turbulent GAM dispersion relation is qualitatively equivalent to the linear GAM dispersion but can have drastically enhanced group velocities. In up-down asymmetric geometry the energy input due to turbulent transport may favor the excitation of GAMs with one particular sign of the radial phase velocity relative to the magnetic drifts and may lead to pulsed GAM activity. 相似文献
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Previously, experiments with microwave signals have shown that evanescent modes can travel faster than light. Several theoretical
investigations have proven that in the case of signals with unlimitedly high frequency components, such superluminal velocities
do not violate Einstein causality, thus group, signal, and energy velocities are
c where c is the vacuum velocity of light. In this letter I shall show that frequency band limitation is a fundamental property of signals and that such signals containing only evanescent modes can violate Einstein causality.
Received: 12 December 1998 / Accepted: 14 December 1998 相似文献
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Slowing a light pulse in a degenerate two-level system is observed with a
double-frequency sweeping technique. The effects of coupling beam intensity,
cell temperature and frequency detunings of the coupling and probe beams in
resonance, on the slowing of light propagation in such a system are
investigated. It is found that group velocities depend strongly on
polarization combinations. A group velocity $v_{\rm g}$=6760m/s of light pulses in
caesium vapour is obtained under the optimal parameters. 相似文献
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Guided wave dispersion curves for a bar with an arbitrary cross-section,a rod and rail example 总被引:1,自引:0,他引:1
Theoretical and experimental issues of acquiring dispersion curves for bars of arbitrary cross-section are discussed. Since a guided wave can propagate over long distances in a structure, guided waves have great potential for being applied to the rapid non-destructive evaluation of large structures such as rails in the railroad industry. Such fundamental data as phase velocity, group velocity, and wave structure for each guided wave mode is presented for structures with complicated cross-sectional geometries as rail. Phase velocity and group velocity dispersion curves are obtained for bars with an arbitrary cross-section using a semi-analytical finite element method. Since a large number of propagating modes with close phase velocities exist, dispersion curves consisting of only dominant modes are obtained by calculating the displacement at a received point for each mode. These theoretical dispersion curves agree in characteristic parts with the experimental dispersion curves obtained by a two-dimensional Fourier transform technique. 相似文献