平成21年度 実績報告書
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教育研究プラットフォームIDER研究成果/ポストドクター・GCOE研究員Mitigation of Phase Fluctuations in Dispersion - Managed Optical Fiber Transmission Systems Mohammad Faisal D ivision of Electrical, Electronic and Information Engineering , Graduate School of Engineering , Osaka University Kitayama Laboratory Abstract Phase - modulated data formats are much promising for future high - speed long - haul optical fiber communication systems. Phase fluctuations due to fiber nonlinearity could be the major limiting factors to achieve the advantages predicted for phase - modulated formats. Phase fluctuations mechanism, as well as estimation of SPM - induced phase noise has been investigated for dispersion - managed (DM) systems. Therefore, upgradation of DM maps has been pr oposed to obtain long transmission line. Phase fluctuations due to XPM are also explored and their mitigation techniques are studied for DM WDM transmission systems. Brief Description In order to meet the ever increasing demand of global broadband data se rvices and advanced Internet applications, telecommunication networks based on fiber - optics are getting huge popularity. The next generation lightwave transmission systems should provide this high capacity and at the same time, at a lower cost. This shifts the research trend from OOK - based system to the phase modulation formats such as DPSK and multilevel PSK/DPSK to enhance the per - fiber transmission capacity. P hase noise due to interaction of fiber nonlinearity and amplifier’s ASE noise has been examined for various DM maps. Therefore, upgraded DM maps are proposed to obtain phase modulated long transmission line by achieving lower phase noise and higher Q - factor [1]. It is found that weaker DM map is suitable for DM soliton transmission whereas stronger D M map is preferable for quasi - linear transmission systems regarding phase noise. The fundamental mechanism of collision - induced phase shift in a DM WDM system has also been investigated. Phase fluctuations due to XPM are calculated for different DM maps and for different bit - rate systems considering RZ pulse. Furthermore, impact of initial pulse spacing, channel spacing and residual dispersion on phase shift has been explored [2]. XPM - induced phase fluctuations could be considerably mitigated by properly choosing channel spacing and residual dispersion. Analytical results are obtained by variational method and are validated by solving the nonlinear Schrödinger equation numerically using split - step Fourier algorithm . Conclusions Finally, it is concluded th at phase fluctuations due to fiber nonlinearity might be a major limiting factor in the way to realize long - haul high speed phase modulated transmission systems. However, these impairments could be mitigated by properly designing DM transmission systems al ong with consideration of other design factors like amplifier spacing, channel spacing, and residual dispersion. References [1] M. Faisal and A. Maruta, “Upgradation of dispersion compensation map for photonic transmission systems,” Proc. of 2 nd Global COE International Symposium (EDIS 2009), Paper WS3 - B1, pp. 111 - 112, Osaka, Japan, Dec 2, 2009 - Feb 2, 2010. [2] M. Faisal and A. Maruta, “Effects of XPM on phase of RZ pulse in dispersion compensated transmission line,” Proc. of ICOCN 2009, Paper co nf09b361, in CD - ROM, Beijing, China, 15 - 17 September, 2009. 109

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