Research On All-optical Wavelength Conversion And Its Application In Radio-Over-Fiber System

Currently,two areas of optical communication network are transmission and access network,which are moving towards the direction of the development of high-speed large-capacity.Researchers pay attention to the problems that how to improve the communication capacity,in the case of limited bandwidth.Polarization multiplexing technique can be used to increase the communication capacity of a single optical fiber.Single carrier technique is used to improve the communication rate of single channel.Moreover,polarization-division-multiplexing quaternary phase shift keying(PDM-QPSK)signal combined by single carrier technique and polarization multiplexing technique,can be used to compensate impairments in the transmission system in digital domain by using optical coherent detection.OFDM technique has the advantage of high spectral efficiency,and in optical communication system,OFDM signal has strong dispersion and polarization mode dispersion(PMD)resistance.Due to the current backbone transmission system using new modulation format has become a trend.In order to enhance the network interconnection and networking,all optical wavelength conversion(AOWC)is adoppted in the optical transmission network node.The characteristics analysis of the AOWC for polarization multiplexing signal,PDM-QPSK signal and OFDM signal are in-depth discussed and studied.And the AOWC based on FWM is applied to the ROF system to produce polarization insensitive optical millimeter.Theses researches are significant in both theory and practice for the future development of optical communication network.The paper includes the following parts:Firstly,according to lack of research on polarization crosstalk of polarization-multiplexed signals during all optical wavelength conversion,we proposed a polarization diversity all-optical wavelength conversion scheme to reduce the crosstalk among the two multiplexed channels for polarization multiplexing system.First,the polarization rotation effect in SOA for polarization-multiplexed signals was presented.Based on the theoretical analysis,two single-polarization wavelength conversions are performing in the two SOAs,and the crosstalk among the two multiplexed channels is reduced.The simulation results demonstrate that the performance of the proposed scheme is improved compared to the conventional scheme.In addition,this scheme can be applied to AOWC multicast system.The simulation results demonstrate that the proposed polarization diversity AOWC multicast system is improved compared to the conventional system.The method provides new idea for the design of all-optical wavelength converter.Secondly,we have theoretically analyzed and experimentally investigated the the AOWC for PDM-QPSK signal using two nonlinear mediums in optical coherent reception system,and the optimal performance of the system was obtained.First,we have theoretically studied the correlation between the SOA's injection current and conversion efficiency,and it between the SOA's injection current and pattern effect.and the effect of the SOA's injection current on the system performance.The results show that there is an optimal SOA's injection current,and the pattern effect on PDM-QPSK signals is much lower than polarization multiplexing nonreturn-to-zero(PDM-NRZ)signals.We have also theoretically and experimentally analyzed that wavelength conversion for the co-polarized pumps wavelength conversion for PDM-QPSK signals in HNLF.We found that the received polarization multiplexing signal can be obtained without crosstalk by adopting polarization diversity coherent reception.Thirdly,we have theoretically and numerically investigated the AOWC for OFDM signal based on four-wave mixing effect in a SOA,and the optimal performance of the system was obtained.We found that FWM effect between the subcarriers of OFDM signal occurs in the AOWC for OFDM signal,and the FWM products have been covered on the original subcarriers.After wavelength conversion,the interferences deteriorate the converted signal.And we found that the FWM between pump and signal become more significant and FWM effect between subcarriers has small effect on the system performance when the injected pump power is high.The optimum condition for the system performance is obtained by adjusting a favarable pump power.Moreover,the transparence of FWM to modulation formats of OFDM signal has been investigated,and the results show that OFDM signals pose limitations to AOWC transparency.In addition,we have theoretically and numerically investigated coherent optical OFDM wavelength conversion system.The simulation results show that the frequency space of the two pumps,line width of the laser and modulation rate have effects on the converted signal.Finally,the principle of AOWC is applied to the ROF system to realize polarization insensitive all-optical up-conversion for multiplicated frequency milimeter-wave generation.Odd order sidebands suppression method was used in two LiNbO3 modulators,and a filter was used to generate optical milimeter-wave.We have also numerically studied the effects of the MZM DC-bias and modulation depth on the system performance,and the optimal performance of the system was obtained.This scheme can reduce the bandwidth requirements of the modulator.The application of OFDM signal can enhance the system transmission performance.On the basis of former reasearch,the principle of AOWC is applied to the ROF system to realize multiplicated frequency milimeter-wave generation was polarization insensitive.We have also numerically studied the effects of the current of SO A on the system performance,and the optimal performance of the system was obtained.In this scheme,polarization controllers to keep the polarization direction of lightwave can be reduced.Therefore,this scheme can reduce the system complexity and cost,it has a strong practical value.