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CH10_Modulation Formats for Optical communications (Amplitude modulation…
CH10_Modulation Formats for
Optical communications
Amplitude modulation formats
nonreturn-to-zero (NRZ)
return-to-zero(RZ)
carrier suppressed return-to-zero (CSRZ)
Field modulation formats
Quadrature phase shift keying (QPSK)
differential QPSK (DQPSK)
Quadrature amplitude modulation (QAM)
通常與coherent detection receiver.搭配
Key factor
Bandwidth efficiency
tolerance to chromatic dispersion and PMD
receiver sensitivity
相同bitrate下，RZ需要更寬的帶寬，因為時域中，脈波寬度僅是NRZ的一半. (一個bit來看)
意味著，RZ格式易與帶寬相依的參數衝突.
CD (chromatic dispersion)
色散。不同波長，在光纖中傳輸速度不等造成長距離傳輸後，訊號變寬. 形成誤碼.
PMD (polarization mode dispersion)
偏極化模態色散。 光波(電磁波)因為快慢軸在光纖中傳輸速度不同，經傳輸後訊號變寬，造成誤碼。
transfer function ripples
10.2 Generation of PRBS patterns and clock recovery