Study On The Performance Of Phase Modulation In 40Gbit/s WDM System

With the rapid development of optical communication technologies, it is possible that Dense Wavelength Division Multiplexing (DWDM) systems would appear, with the single optical channel bit rate up to, even more than 40Gbit/s, with the transmission reach beyond 1,000 kilometers, and with a capacity of network exceed to one Terabit/s. Especially with the maturation of the high speed optoelectronic devices in recent years,40 Gbit/s systems are capable to business-oriented. However, the upgrade of signal bit rate will bring about several more obvious transmission injury in optical fiber. Compared to intensity modulation format, phase modulation format have greater tolerance to the Optical Signal to Noise Rate (OSNR), Chromatic Dispersion, Polarization Mode Dispersion and Non-linear effect. But there are still many problems in phase modulation format application and need futher study.First we studied the modulation and demodulation principle of phase modulation format DPSK and DQPSK in this paper, and then introduced an experiment base on these two modulation formats in long haul 40Gbit/s WDM transmission system. Through the experiment we get different performance response to transmission injury for different modulation formats, and to obtain several critical transmission system parameters that not only can be used as references to select an appropriate modulation format for existing high speed communication systems and optimize the performance. In addition, we analysis the nonlinear phase noise induced by XPM, and the BER of DPSK and DQPSK systems to compare their different performance with XPM. The result indicates that DQPSK is easier to be affected by nonlinear noise. Finally we introduce an 40Gbit/s and lOGbit/s mixed transmission experiment, to discover the optimal configuration of DPSK and DQPSK transmission systems, that can be used as a reference to application in reality.