Cross-phase Modulation In Wavelength Division Multiplexing Systems

Wavelength Division Multiplexing(WDM) is a new domain in optics communication, and is attracting more and more attention. Though WDM can improve the bandwidth of high speed net effectively, it also causes some disadvantages. This paper will discuss the effect of cross-phase modulation(XPM). For a less channel system, people have gained many results in theory and practice; but for the condition which capacity is bigger than 10Gb and channel spacing smaller than 0.8nm; the XPM on erbium-doped fiber amplifiers(EDFA) is obvious, although there are several experimental reports on this, the theory research is almost empty, so to establish the theory model is significant.This paper will use small signal analysis and split-step Fourier to solve the complex nonlinear Schrodinger equation (NLSE). In the frequency domain, the analysis resolve of NLSE can explain the initial stage of the modulation instability. On the other hand, the whole character of the modulated unstable continuous waves can be discussed by the small signal analysis. The results are suitable to normal or abnormal dispersion regimes. In addition, the conversion matrix which describes the conversion between the intensity and phase modulation (or noise) in nonlinear dispersion medium is derived, it will be valid for any frequency or intensity modulation, and the method can be used to analyze the dispersion effect (including the β₃) in fiber.Based on the result of small signal analysis, the effect of modulation instability on wavelength-division multiplexing (WDM) system can be discussed in details as follows: modulation instability decrease the signal's power, amplifier the noise and decreases the SNR of WDM system. Besides, the effect of modulation instability is different from different channel. The effect on short waves is stronger than that of the long wave; it will make every channel's SNR have a deviation and there is a big SNR on the long wave. The deviation will accumulate with fiber length. For a system or a...