共查询到20条相似文献,搜索用时 31 毫秒
1.
研究了导波在正交各向异性黏弹性复合板中传播的色散特性、波结构及功率流密度。基于二维平面运动方程,采用谱有限元方法得到了导波色散的特征方程。分析了正交各向异性黏弹性板中各向异性和黏性对能量速度和波结构的影响,以及基底对导波功率流密度的影响。数值研究结果表明:导波沿纤维方向传播的能量速度大,材料的黏性对速度影响较小,但会减小波结构的幅度;在高频时,基底的存在使两个基本模态的功率流密度分别集中到波导的上下表面,形成弱色散、高衰减及无色散、零衰减的表面波。数值模拟结果为导波用于复合材料定量无损检测和性能评价提供理论依据。 相似文献
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提出谱有限元方法研究层状各向异性复合板中导波的色散特性和波结构。基于三维弹性动力学方程,用有限元方法离散波导截面,波传播方向的位移用简谐波表示,得到了导波色散的特征方程。分析了单层和双层复合板中导波沿不同方向传播的色散特性和波结构,讨论了双层复合板中层厚比对相速度的影响。数值研究结果表明:导波的对称模态沿纤维方向传播时在较宽的频率范围内保持弱色散状态。双层复合板中导波基本模态的相速度在低频时受层厚比的影响较明显,随着频率的增加趋向于相速度较低的材料。数值模拟结果为导波用于复合材料定量无损检测和性能评价提供理论依据。 相似文献
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We report the observation of a novel nonlinear optoacoustic phenomenon, that we name forward stimulated interpolarization scattering. When two frequency-offset laser signals are colaunched into orthogonally polarized guided modes of a birefringent small-core (1.8 μm diameter) photonic crystal fiber, a pattern of axially moving polarization fringes is produced, with a velocity and spacing that depends on the frequency offset. At values of frequency offset in the few-GHz range, the pattern of moving fringes can perfectly match the phase velocity and axial wavelength (3.9 mm) of the torsional-radial acoustic mode tightly guided in the core. An intense optoacoustic interaction ensues, leading to efficient nonlinear exchange of power from the higher frequency (pump) mode to the orthogonally polarized lower frequency (Stokes) mode. A full-vectorial theory is developed to explain the observations. 相似文献
4.
Maryam Karimi 《Optik》2014
Holey fibers (HFs) can be used as amplifier in optical communication systems. These new fiber structures have flexibility to change the fiber parameters such as refractive index of guided mode, air filling factor (AFF), V number, group velocity dispersion (GVD) and numerical aperture, only by the change of the hole size and air-hole spacing. In this paper we will use improved fully vectorial effective index method (IFEIM) to analyze the erbium doped holey fiber amplifier (EDHFA) with hexagonal unit cell. The range that core size can change in any air-hole spacing will determine and the growth of core size in the amplifier character such as maximum gain and optimum length will study. By determination of single mode region the effect of pump power and dopant concentration growth, on the amplifier parameter will define. 相似文献
5.
Gain guided and index anti-guided fiber, being a new kind of fiber with a great potential application on large mode area lasing devices, has the inevitable geometric curvature, which induces field deformation and bending losses. In this paper, the method of complex-value extended Fourier-Bessel series is introduced on optical field deformation and bending losses by geometric curvature in the case of this new fiber. Comparing with conventional fibers, gain guided and index anti-guided fiber has better performance on anti-curvature; the quantity of optical intensity centre being shifted from fiber geometric center is less than the case of conventional index guided fibers; and the bending losses decrease dramatically with the increase of curvature radius. 相似文献
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手征参数对光纤中模式特性的影响 总被引:10,自引:2,他引:8
对圆芯和包层都是手征介质的阶跃型手征光纤进行了解析求解,导出了模式特征方程,给出了手征光纤中模式场,光强和光功率分布的表达式。分别研究了纤芯和包层中的手征参数对模式特性的影响.。 相似文献
8.
We report a novel fiber design for obtaining long period gratings (LPGs) having a broad transmission spectrum. These gratings are based on guided to guided mode coupling in a staircase profile fiber. Numerical simulations predict 20 dB bandwidths as high as 100 nm and an estimated insertion loss of less than 1 dB. Such broadband LPGs are expected to find applications in many all fiber components. 相似文献
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长周期光纤光栅中的包层模谐振 总被引:6,自引:1,他引:5
本文给出了光纤中包层模的电场形式,指出包层膜的电场形式与弱导光纤中导模的电场形式不同,对光纤中基模与包层模电场沿光纤横截面分布的重叠情况的分析表明,长周期光纤光栅除了能将HE11导模耦合到HE1p包层模外,也可以将其耦合到EH1p包层模。基于耦合模理论的计算表明,耦合到EH1p和EH1,p-1包层模的耦合波长相近,对于典型的单模光纤,当p>4时耦合到这两个模式的耦合系数是可比的。 相似文献
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Jianfeng Dong 《Optics Communications》2010,283(4):532-536
Guided and surface modes in the chiral nihility fiber consisting of a chiral nihility metamaterial core with an achiral cladding have been investigated. The dispersion equations of guided and surface modes in the chiral nihility fiber and their cutoff frequencies are derived. Dispersion curves of guided and surface modes are presented and the effect of chirality parameter on dispersion curves is discussed in detail. Some novel propagation characteristics are found. 相似文献
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The coupling of an ultrashort laser pulse into a single-mode optical communication fiber gives rise to two propagating pulses as a result of the excitation of two guided modes, the fundamental, LP(01) , and the leaky, LP(11) . Such a phenomenon provides a new approach to the study of the propagation properties of the LP(11) mode. An experiment with tunable 110-fs pulses at a wavelength near 1550 nm is described. Information about the group velocity, the polarization-rotation length, the attenuation coefficient, and the cutoff wavelength of the LP(11) mode is obtained in a simple and direct way for various fibers. 相似文献
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Electromagnetic field confined and tailored with a few air holes in a photonic-crystal fiber 总被引:1,自引:0,他引:1
A. M. Apetrei J. M. Moison J. A. Levenson M. Foroni F. Poli A. Cucinotta S. Selleri M. Legré M. Wegmüller N. Gisin K. V. Dukel’skii A. V. Khokhlov V. S. Shevandin Yu. N. Kondrat’ev C. Sibilia E. E. Serebryannikov A. M. Zheltikov 《Applied physics. B, Lasers and optics》2005,81(2-3):409-414
Conventional and scanning near-field optical microscopy techniques are cross referenced to femtosecond nonlinear-optical measurements and finite-element numerical simulations to visualize and analyze a strong confinement of electromagnetic radiation in guided modes of a photonic-crystal fiber with only a few air holes surrounding the fiber core. A nonlinear coefficient of about 120 W−1 km−1 is achieved at the wavelength of 670 nm for a fused-silica fiber with a full hexagonal cycle of closely packed air holes around the fiber core. The removal of a single element from this array of air holes is shown to frustrate field confinement in guided modes, leading to mode leakage. 相似文献
17.
S. O. Konorov A. B. Fedotov O. A. Kolevatova V. I. Beloglazov N. B. Skibina A. V. Shcherbakov A. M. Zheltikov 《JETP Letters》2002,76(6):341-345
Waveguide modes of microstructure fibers with a hollow core and a two-dimensionally periodic cladding are studied experimentally and theoretically. The spectrum of modes guided in the hollow core of these fibers displays isolated maxima, indicating that waveguiding is supported due to the high reflectivity of the fiber cladding within photonic band gaps. The main properties of the spectrum of modes guided in a hollow core of a photonic-crystal fiber and radiation intensity distribution in these modes are qualitatively explained in terms of the model of a periodic coaxial waveguide. 相似文献
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We propose an idea to excite localized modes in a photonic crystal (PC) waveguide without ruining the discrete translational symmetry of the lattice. This can be done by arranging dispersive elements having negative permittivity over a desired frequency range into a periodic structure. We demonstrate numerically the realization of a cavity mode inside the air region of a geometrical defectless two-dimensional square-lattice PC consisting of polaritonic cylinders placed in air matrix. The corresponding waveguide structure in the form of a PC fiber supports the cavity mode as a guided mode to propagate along the guiding direction at very small propagation constant with near zero group velocity. These localized modes can be recognized as localized defectless modes inside the structure with four-fold symmetry. 相似文献
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The novel characteristics of guided modes in the chiral negative refractive index fiber are investigated theoretically in this letter.We derive the characteristic equation of guided modes.Based on two types of chiral metamaterial parameters,we present the dispersion curves,energy flux,and power of guided modes.Some abnormal features,such as the existence of surface mode and dispersion curves with different shapes,intersection of dispersion curves of different guided modes,negative energy flux in the achiral cladding,and zero power at some normalized frequencies,are found in the chiral negative refractive index fiber. 相似文献
20.
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