光纖色散ppt課件(存儲(chǔ)版)
【正文】 剩下的是材料色散和波導(dǎo)色散。 15 50 nm13 10 nm色散ps/ nm ? km普通光纖 (SMF)非色散位移光纖 （ NDSF ， ）已有光纖的 95%波長(zhǎng) ?色散位移光纖 （ DSF , ）非零色散位移光纖 （ NZDSF , ）180DWDM波長(zhǎng)范圍三種光纖色散情況比較 正常色散區(qū) 反常色散區(qū) Group Velocity Dispersion (GVD) ? Normal Dispersion Regime :the long wavelengths travel faster than the short ones! Thus after travelling on a fibre wavelengths at the red end of the pulse spectrum will arrive first. This is called a positive chirp! ? Anomalous Dispersion Regime: the short wavelengths (blue end of the spectrum) travel faster than the long wavelengths (red end). After travel on a fibre the shorter wavelengths will arrive first. This is considered a negative chirp. Material (Chromatic) Dispersion ? This is caused by the fact that the refractive index of the glass we are using varies (slightly) with the wavelength. Some wavelengths therefore have higher group velocities and so travel faster than others. Since every pulse consists of a range of wavelengths it will spread out to some degree during its travel. Waveguide Dispersion ? The shape (profile) of the fibre has a very significant effect on the group velocity. This is because the amount that the fields overlap between core and cladding depends strongly on the wavelength. The longer the wavelength the further the the electromagic wave extends into the cladding. ? since a greater proportion of the wave at shorter wavelengths is confined within the core, the shorter wavelengths “see” a higher RI than do longer wavelengths. Therefore shorter wavelengths tend to travel more slowly than longer ones. Polarisation Mode Dispersion (PMD) ? There is usually a very slight difference in RI for each polarization. It can be a source of dispersion, usuall
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