非线性光学（第三章）.pptVIP

中心对称介质中，二阶非线性 极化率为零，最低阶非线性极化为三阶， 三阶非线性光学现象包括： 光学克尔效应 光致折射率效应 高斯光束自聚焦 四波混频 光孤子 受激拉曼散射 受激布里渊散射 （1）高斯光束的自聚焦 （2）高斯光束的自陷 （3）高斯光束的自散焦 光纤损耗单位：dB/km Chromatic Dispersion The refractive index of silica is approximately by Sellmeier equation Effects of fiber dispersion are account for expanding the mode-propagation constant in a Taylor series Single mode fiber support two degenerate modes that are polarized in two orthogonal direction. The modal birefringence is defined by a dimensionless parameter For a given value of birefringence, the two modes exchange their powers in a periodic fashion as they propagate inside the fiber, beat length is defined as 3.5.2 光纤的非线性特性 (1) Nonlinear Refraction The lowest-order nonlinear effects in optical fibers originate from the third-order susceptibility Third-harmonic generation Four-wave mixing Nonlinear refractive index (2) Stimulated Inelastic Scattering A second class of nonlinear effects results from stimulated inelastic scattering in which the optical field transfers part of its energy to the nonlinear medium. Stimulated Raman Scattering Stimulated Brillouin Scattering 习 题： 《非线性光纤光学原理及应用》（第二版） pp.16 1.1 1.2 1.8 1.9 3.5 光纤中的非线性现象 3.5.1 光纤的特性 Fiber Losses Fiber losses originate from contributing of the material absorption and Rayleigh scattering dominantly One feature of chromatic dispersion is that pulses at different wavelengths propagate at different speeds inside a fiber because of mismatch in their group velocities. This feature leads to a walk-off effect: The walk-off length is defined as Another feature of chromatic dispersion is pulses broadening. This feature is measured by dispersion length defined as Polarization-Mode dispersion is jth order susceptibility is a tensor of rank (j+1) As silica is a symmetric molecule, fiber do not normally exhibit second-order nonl