光纤知识点概念.docVIP

1模式的概念 Concept of Modes: Propagation of light along a waveguide can be described in terms of a set of guided electromagnetic waves called Mode of waveguide. 2模式的分布特性 Each Mode is a pattern of electric and magnetic field distribution that is repeated along the fiber at equal intervals. A certain discrete number of Modes are capable of propagating along the waveguide. 本征值方程是一个关于( 的以( 为参量的超越方程，通常使用数值方法求解。对于不同的( ，可存在一组离散的( 解，每一个( 对应能在光纤中传播的光场的一种空间分布，这种空间分布在传播过程中只有相位的变化，而没有分布形状的变化，将这种空间分布称为模式。根据不同的条件，光纤中可能存在许多模式 3 5简并模方法： 每个LP0m模由HE1m模导出；每个LP1m模由TE0m、TM0m、HE2m构成；每个LPvm模（v1）由HEv+1,m、EHv-1,m构成。 例如LP01模只包含基模HE11LP11模由TE01、TM01、HE21构成； 6阶跃光纤中的功率分布 当V→∞时，它的能量将聚集在纤芯中； 当V→Vc时，能量的大部分是在包层里，这时的导波将成为辐射模。 第三章 Signal attenuation:is one of the most important properties of an optical fiber. It largely determines the maximum unamplified or repeaterless between a transmitter and a receiver. The basic attenuation mechanisms in a fiber: Absorption Scattering losses Radioactive losses microscopic variations in the material density compositional fluctuations structural inhomogeneities defects occurring during fiber manufacture. Radiative losses fiber undergoes a bend of finite radius of curvature. Fiber can be subject to two types of bends: 1.macroscopic bends: having radii that are large compared with the fiber diameter. 2 random microscopic bends: can arise when the fibers are incorporated into cables. Intramodal Dispersion Intramodal Dispersion is pulse spreading that occurs within a single mode. The spreading arises from the finite spectral emission width of an optical source. This phenomenon is also known as group velocity dispersion. 1Material Dispersion ：arises from the variation of the refractive index of the core material as a function of wavelength . 2Waveguide Dispersion：occurs because a single-model fiber confines only about 80% of the optical power to the core. 3The other factor giving rise to pulse spreading is intermodal delay, which is a result of e