光纖色散ppt課件(參考版)
2025-05-15 07:07本頁面
【正文】 G652: ). ? 短波長過補償，長波長欠補償。 ? External cavity DBR laser: .01 nm ? Using more plex signal coding rather than simple OOK. ? Using WDM(a Gbps signal has 1/4 of the problem with dispersion as a 10 Gbps signal). Dispersion Shifted Fibre ? dispersion shifted fibre is designed with a dispersion zero point at around 1550 nm. ? However, it is not always possible or indeed desirable： ? In many cases we can39。材料色散與模間色散合成的總色散為 色散和帶寬的關(guān)系： 總時延差： ?? 1ncB)())(( 12 HzDB?? ???材料色散限制帶寬 波導(dǎo) 色散限制帶寬 2/1222 )(gms ???? ??＝總其中 ?s， ?m， ?g分別為模式色散，材料色散和波導(dǎo)色散引起的時延差。但是，當(dāng)光源為發(fā)光二級管 (LED)時，由于其譜寬大約為 30— 50nm，故增加了材料色散的影響。對于多模漸變型光纖，如果采用激光器 (LD)作光源，其譜寬一般為 12nm，故可忽略材料色散。在多模光纖中，波導(dǎo)色散與材料色散相比，常常可以忽略。如果把模間色散平衡掉，則剩下的是材料色散和波導(dǎo)色散。 處材料色散近似為零 , 因而稱為零材料色散波長。 通常，材料色散比波導(dǎo)色散大兩個量級。它們分別用色散系數(shù) σ c和 σ ω 表示。 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 ?色散位移光纖 （ DSF , ）非零色散位移光纖 （ NZDSF , ）180DWDM波長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
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