不完全色散補償對光纖通訊系統的影響

• Main Authors: Tsung-Kun Lin, 林宗崑
• Other Authors: Senfar Wen
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/24098573493558416628

碩士 === 中華大學 === 電機工程學系碩士班 === 88 === To improve the fiber communication system of high speed and long distance, dispersion compensation technologies have been used to compensate for fiber dispersion that distorts signal pulse. On the other hand, fiber nonlinearities deteriorate signal pulse. In this thesis, to tailor the effect of fiber nonlinearities on signal pulse, the system of incomplete dispersion compensation is theoretically studied. The considered bit rate and transmission distance are 10 Gbit/s and 9000km, respectively. Fiber loss and dispersion are compensated every 50 km by optical amplifier and dispersion compensation fiber (DCF), respectively. NRZ signal format is used. During signal transmission, fiber dispersion is not completely compensated for every compensation period so that signal-noise four wave mixing (FWM) is reduced and self-phase modulation (SPM) enhances pulse broadening or compression. It is found that, when the pulse is compressed too much, it cannot be further compressed and it is broadened in stead. A DCF is used to tailor the pulse shape after signal transmission. Because of the frequency chirping induced by SPM, signal pulse can be compressed by the post dispersion compensation for either signal pulse is broadened or compressed during transmission. Formulas are derived to estimate the pulse width of the signal without amplifier noise at the output of every compensation period and after post dispersion compensation. Wave equation is numerically solved to verify the formulas. Including amplifier noise, the transmission system is numerically simulated and Q factor is obtained. It is found that proper pulse broadening or compression during signal transmission improves Q factor. For proper pulse broadening, the effect of fiber nonlinearities is reduced because of lower optical power and the quality of pulse shape is better when it is compressed at receiver. For proper pulse compression, though the effect of fiber nonlinearities is enhanced, signal power is well confined within its corresponding time slot and signal-to-noise ratio is improved. It is found that, when the pulse is broadened during transmission, the better change ratio of pulse width is about 10% to 70% after transmission and the optimal ratio is around 30%. When the pulse is compressed during transmission, the better condition is that the pulse is compressed and then is broadened but the change ratio of pulse width after transmission is still negative and is —10% to —20%. For either the pulse broadening or compression during transmission, the best pulse shape after the post dispersion compensation at receiver is that the pulse width is compressed about 30%. As system performance depends on signal pulse width, the derived formulas estimating pulse width are helpful for system design.