Study On WDM Channel Crosstalk Suppression Methods

With the deepening of society informationalization, the IP services, as a representativeof data services, have an explosive growth. As a result, the field of communication hasdeveloped rapidly. New communication technologies and new programs have sprung up. But,there are also numerous problems in it. Application of new technologies can solve aparticular aspect of the problem, but coming with other problems inevitably. If theseproblems are not solved appropriately, the results of accumulation are the declining of thesystem performance and the increasing of the system cost, restricting the increasing of thecommunication capacity and can’t meet people’s growing needs of communication capacity.Compared to the cable communication, the fiber communication has greatertransmission capacity, longer transmission distance and stronger anti-jamming capability, soit has become the development trend of the communication technology. In the developingprocess of the fiber communication, the wavelength division multiplexing technology cameinto being. There is only one way of signal in one fiber in the past fiber communicationsystems. So, more fibers should be lay in order to increase the capacity of the system, itmakes the cost go up significantly. But the wavelength division multiplexing technology canachieve contemporary transmission of multiple signals in the same fiber, which can increasethe system capacity significantly, so it has been considered as an effective method to solvethe communication capacity problem. But, as been said before, the application of newtechnology will inevitably come with new problems, including group velocity dispersion(GVD), polarization mode dispersion (PMD), the amplifier noise, transient effect, thechannel crosstalk and fiber nonlinearity. The channel spacing is becoming smaller andsmaller in order to increase the system capacity in WDM system, which causes the channelcrosstalk problem in the system getting worse. This article is focused on the study of thechannel crosstalk problem. The main works lie:First, this article gave an introduction of developing process of WDM technology,developing status of WDM technology, discussed the advantages of WDM technology andintroduced the status of study on WDM channel crosstalk suppression methods.Second, the article analyzed the working principle of WDM system,gave a briefintroduction of the classification and composition of the WDM system, then discussed thecapacity of WDM system. This article also analyzed several factors affecting the transmission capacity and transmission distance of WDM system, introduced three keytechnologies of WDM system, which are light source technology, optical amplificationtechnology and optical filtering technology.Then, we classified the channel crosstalk in the WDM system, had a talk about themajor sources producing non-linear crosstalk, including four-wave mixing, stimulatedRaman scattering and cross-phase modulation, analyzed the reasons causing them and themethods to restrain it. Then we studied the linear crosstalk, especially the same frequencycrosstalk, discussed the reasons which cause them and attempt to find methods to restrain it.We find that filtering can reduce the same frequency crosstalk in WDM system and analyzedtwo solutions to this problem, of which one is the Nyquist wavelength division multiplexing,the other is the coherent optical orthogonal wavelength division multiplexing. Both of thesemethods can avoid the same frequency crosstalk, while ensuring high spectral efficiency ofthe system.Finally, we explored the way to eliminate the same frequency crosstalk by the Nyquistwavelength division multiplexing method, and used the VPI simulation software as anexperimental platform, had an attempt of electric domain filtering and optical domainfiltering. At last, we found an effective method of filtering by which we can get the ideal sincwaveform signals. We also stimulated the WDM system using the Nyquist wavelengthdivision multiplexing method. Stimulation results show that the adjacent channel crosstalk isgreatly reduced, proving the feasibility and rationality of the filtering method using Nyquistwavelength division multiplexing.