Gb / s soliton transmission in a densely dispersion - managed ber in the presence of variable dispersion and polarization - mode dispersion

One of the major limitations on transmission speed per single-channel in dispersion-managed soliton (DMS) systems is soliton interactions between neighboring pulses induced by large pulse breathing within one dispersion-management period [1]. To o vercome this limitation, densely dispersion-managed soliton (DDMS) system was recently proposed, and it is numerically demonstrated that 80 Gb/s soliton transmission over 9,000 km may be possible without any active controls [2]. For further increase of bit-rate per single-channel up to 160 Gb/s, however, it is indispensable to assess the impact of dispersion slope and polarization mode dispersion (PMD), which may deteriorate transmission characteristic signicantly in such ultra high-speed transmission. Furthermore, one should assume large variation of group-velocity dispersion (GVD) for practical dispersion attened bers. In dispersion-managed systems schematically shown in Fig. 1, soliton interaction between neighboring pulses can be minimized by satisfying the condition S 1:6 in a lossless case [1], where S is dened as S = j 1 z 1 0 2 z 2 j=t s and t s is FWHM of DMS when it is transform-limited. Given the amplier spacing z a and the value of both anomalous and normal dispersion, this condition is satised by a proper choice of the number of DM period n within one amplication period (n = z a =(z 1 + z 2)). For instance, when z a = 4 0 k m , d 1 = 2 :5 ps/nm/km and d 2 = 02:49 ps/nm/km, n becomes 20. Fig. 2 shows dependence of collision distance on n (and corresponding S). The interaction forces become stronger for n > 20 (n < 20), since the stationary pulse approach to sech solitons [3,4] (the pulse width oscillates too much.). Based on this observation, it is expected that even when ber GVD varies owing to the fabrication of dispersion attening, soliton interaction may be minimized by arranging dispersion prole such that it satises the condition S = 1 :6. As one approach, given a pair of bers having anomalous and normal dispersion d 1 and d 2 respectively, the length of each section z 1 and z 2 may be determined so that S becomes 1.6 and the average dispersion is constant along the line. Fig. 3 shows an example of dispersion prole based on this method, where we assume bers having Gaussian distribution in GVD with the average of 0 and the variance of 3.0, and total average …