Jianjun Yu, Yang Bojun, Keijian Guan, Member, IEEE Qimin Yang, Xiaoguang Zhang, and Jianguo Yu. Abstractâ In order to realize long amplifier spacing, long ...
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IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 9, NO. 7, JULY 1997
Dispersion-Allocated Soliton Technology with Long Amplifier Spacing and Long Distance Jianjun Yu, Yang Bojun, Keijian Guan, Member, IEEE Qimin Yang, Xiaoguang Zhang, and Jianguo Yu
Abstract— In order to realize long amplifier spacing, longdistance soliton transmission, dispersion-allocated fiber was optimized. Dispersion-decreasing-allocated fiber is favorable to transmit stable soliton over long distance. Fiber loss plays an important role in stable soliton transmission with the dispersion-allocated fibers. In order to realize soliton bidirectional transmission, symmetrical configuration of the dispersion-allocated fiber within an amplifier spacing must be designed, so the dispersion-decreasingallocated fiber is not favorable to soliton bidirectional transmission. Index Terms— Bidirectional transmission, dispersion-allocated technology, fiber loss, soliton.
R
ECENTLY, people are fascinated by the dispersionallocated soliton technology because of its many virtues [1]–[7]. The most apparent advantage is that it is not necessary for every fiber segment to have anomalous dispersion. As long as the average group velocity dispersion (GVD) is anomalous or zero [1]–[3], [7], a soliton can propagate even in fibers with normal GVD. Reference [2] presented three constraints that must be satisfied to realize stable soliton transmission. We must point out here that the conclusion was obtained with fiber loss not considered. By numerical analysis we find that the three constraints in [2] are only true with short amplifier spacing. When the amplifier spacing is longer, the soliton can not be maintained if just to satisfy the three constraints. This means the pulsewidth at the start of each amplifier cell can not regenerate its original width at the end of each amplifier cell no matter how large the input power is. In this letter, we present a model, and the analysis result shows that there exists a definite law to allocate different dispersion fibers in order to realize long amplifier spacing and long distance soliton transmission. In our model, the four kind typical configurations within an amplifier spacing are constituted by the four different dispersion fiber with the same length. They are shown in Fig. 1. The four segments have dispersions 0.5 ps/nm/km, 0.5 ps/nm/km, 1 ps/nm/km, 1.5 ps/nm/km, respectively. The average GVD of the four kind of configuration fiber is 0.625 ps/nm/km in the center wavelength 1.55 m, so it is in the anomalous region, and satisfies soliton transmission condition. Each segment is taken to be equal length. The fiber loss is 0.3 dB/km, the valid fiber area is taken to be 60 m , Manuscript received October 14, 1996; revised March 12, 1997. This work was supported by the Ministry of Posts and Telecommunications and by the National “863” High Technology Project. The authors are with the Beijing University of Posts and Telecommunications 192#, Beijing 100088, China. Publisher Item Identifier S 1041-1135(97)04945-8.
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Fig. 1. The four typical configurations of dispersion-allocated fibers.
Fig. 2. The evolution of the pulsewidth broadening coefficient in A, C, and D configurations over 40 km with no fiber loss being considered. A, C, and D curves represent the evolution of the pulsewidth broadening coefficient in A, C, and D configurations, respectively.
and Kerr coefficient is 3.2 10 m /W. To simpify the problem we have chosen to neglect ASE noise of EDFA and higher order dispersion throughout. The propagation behavior of the ultra short pulse in the single-mode fiber is described by the nonlinear Sch¨odinger equation. The split-step Fourier Transform method is used for the calculation. With the fiber loss neglected, the amplifier 40 km, nonchirped initial pulsewidth 10 ps, spacing the evolution of the pulsewidth broadening coefficient in the four kind configurations within the amplifier spacing is shown in Fig. 2. Curves A, C, and D represent the evolution of the pulsewidth broadening coefficient in A, C, and D configurations, respectively. Because the soliton can not be maintained in configuration B, we do not show the evolution of the pulsewidth broadening coefficient in configuration B in Fig. 2. When the repetitive frequency is 1 GHz, the needed
1041–1135/97$10.00 1997 IEEE
JIANJUN et al.: DISPERSION-ALLOCATED SOLITON TECHNOLOGY
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40 km with fiber loss Fig. 3. (a) The evolution of the pulsewidth broadening coefficient in A, B, C, and D configurations over an amplifier spacing considered. A, B, C, and D curves represent the evolution of the pulsewidth broadening coefficient A, B, C, and D configurations, respectively. (b) The 60 km, curve B and curve D evolution of the pulsewidth broadening coefficient in configuration B and configuration D over an amplifier spacing represent the evolution of the pulsewidth broadening coefficient in configuration B and configuration D, respectively. (c) The evolution of the pulsewidth 80 km. broadening coefficient in configuration B over an amplifier spacing
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energy to maintain the fundamental soliton transmission in A, C, and D configurations is 0.093, 0.098, and 0.24 mW, respectively. We can see from Fig. 2 that the change of the pulsewidth in configuration A and configuration C is smaller than that in configuration D, which means that the stability in configuration A and configuration C is better than that in configuration D. But fiber has intrinsic loss in the real situation. If we take the fiber loss into account, we may find different results, so the results obtained without fiber loss may be inaccurate. Fiber loss will be taken into account in the following discussion. The evolution of the pulsewidth broadening coefficient over an amplifier spacing 40 km is shown in Fig. 3(a). Curves A, B, C, and D represent the evolution of the pulsewidth broadening coefficient in A, B, C, and D configurations, respectively. The input mean power to maintan the fundamental soliton and the stability of soliton transmission are shown in Table I. We can see the stability and input mean power are different in different configurations. When the amplifier spacing is 40 km, the evolution of the pulsewidth broadening coefficient over 4000 km in dispersionallocated fiber line with A, B, C, and D configurations as an amplifier cell is shown in Fig. 4. (The input power is equal to the power to maintain the fundamental soliton transmission, the amplifier gain is equal to the fiber loss within the amplifier spacing). A, B, C, and D curves represent the evolution of the pulsewidth broadening coefficient in dispersion-allocated fiber line with A, B, C, and D configurations as an amplifier cell, respectively. We can see that the soliton can be maintained in dispersion-allocated fiber line with A, B, C, and D configurations as an amplifier cell, and the stability is fairly good. When the amplifier spacing is 60 km, the soliton can be maintained in configuration B and configuration D. However, no matter how large the input power is, the soliton can not be maintained in configuration A and configuration C. Because the difference between the output pulsewidth and the input pulsewidth is not big (the output pulsewidth is about 1.2 times than the input width), we can define the type transmission as quasi-soliton transmission. The evolution of the pulsewidth broadening coefficient in configuration B and configuration
TABLE I THE INPUT MEAN POWER TO MAINTAIN THE FUNDAMENTAL SOLITON AND SOLITON TRANSMISSION STABILITY IN THE FOUR KINDS OF CONFIGURATIONS OF DISPERSION-ALLOCATED FIBERS
D over an amplifier spacing is shown in Fig. 3(b). Curve B and curve D represent the evolution of the pulsewidth broadening coefficient in configuration B and configuration D, respectively. In order to maintain the fundamental soliton in configuration B and configuration D, the needed input mean power is 0.39 mW and 0.6 mW, respectively. In order to maintain the fundamental quasi-soliton transmission in configuration A and configuration C, the needed input mean power is 0.8 and 0.7 mW, respectively. When the amplifier spacing is 60 km, the evolution of the pulsewidths broadening coefficient over 1200 km in dispersion-allocated fiber line with A, B, C, and D configurations as an ampifier cell are shown in Fig. 5. A, B, C, and D curves represent the evolution of the pulsewidth broadening coefficient in dispersion-allocated fiber link with A, B, C, and D configurations as an amplifier cell, respectively. We can see that the best stability is in configuration B, the second is in configuration D, and the stability in configuration C and configuration A is poor. When the amplifier spacing is 80 km, soliton can be maintained only in configuration B. The evolution of the pulse broadening coefficient in configuration B over an amplifier spacing 80 km is shown in Fig. 3(c). When the repetitive frequency is 1 Gb/s, the input mean power to maintain fundamental soliton is 0.53 mW. The evolution of the pulsewidth broadening coefficient over 1200 km in dispersion-allocated fiber line with configuration B as an amplifier cell and 80-km amplifier spacing is shown as E curve in Fig. 5.
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IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 9, NO. 7, JULY 1997
Fig. 4. The evolution of the pulsewidth broadening coefficient over 4000 km in dispersion-allocated fiber line with A, B, C, and D configurations as an amplifier cell, the amplifier spacing 40 km and fiber loss being considered. A, B, C, and D curves represent the evolution of the pulsewidth broadening coefficient in dispersion-allocated fiber line with A, B, C, and D configurations as an amplifier cell, respectively.
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of dispersion-allocated fibers satisfies three constraints in [2]. However, when the amplifier spacing is increased, the soliton can not be maintained in some configurations of dispersion allocated fibers. So not only three constraints should be satisfied, but the different dispersion fibers must also be appropriately allocated. The soliton transmission stability in configuration B is the best, and the soliton can be stably transmitted in configuration B over an amplifier spacing 80 km. After having analyzed the feature in configuration B, we can find that it is favorable for soliton to transmit long amplifier spacing and long haul that different dispersion fiber is allocated according to dispersion decreasing (GVD from positive maximum to negative); Configuration C is the same as configuration B except that the input and output directions are exchanged with each other. When the amplifier spacing is 80 km, the soliton can be maintained in configuration B, however soliton can not be maintained in configuration C, and the soliton stability and input power to maintain the fundament soliton are not the same in configuration B and configuration C even if the amplifier spacing is 40 km, so the dispersion-decreasing-allocated fiber which was used to realize long amplifier spacing soliton transmission is not beneficial for soliton bidirectional transmission [8]. We think that the configuration of the dispersion-allocated fiber within an amplifier spacing must be designed to have symmetry to transmit soliton bidirectionally. The configuration can be designed as the configuration of Fig. 1 in [2]. Because there exists a contradiction between the dispersion-decreasingallocated fiber and soliton bidirectional transmission, we must solve it in a reasonable method. REFERENCES
Fig. 5. The evolution of the pulsewidth broadening coefficient over 1200 km in dispersion-allocated fiber line with A, B, C, and D configurations 60 km and fiber loss being as an amplifier cell, the amplifier spacing considered. A, B, C, and D curves represent the evolution of the pulsewidth broadening coefficient in dispersion-allocated fiber line with A, B, C, and D configurations as an amplifier cell, respectively. Curve E represents the evolution of the pulsewidth broadening coefficient in dispersion-allocated fiber line with configuration B as an amplifier cell of 80-km amplifying spacing.
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From the above numerical analysis, we can find that the results are different or reverse when fiber loss is taken into account. When the fiber loss is neglected and the ampli40 km, soliton can not be maintained in fier spacing configuration B, and the soliton can be maintained in A, C, and D configurations. But when the fiber loss is taken into account, soliton can be maintained in A, B, C, and D configurations. When the amplifier spacing is 60 km, the soliton can only be maintained in configuration B and configuration D, so fiber loss plays a very important role and it can not be neglected. A, B, C, and D configurations
[1] M. Nakazawa and H. Kubota, “Optical soliton communication in a positively and negatively dispersion-allocated optical fiber transmission line,” Electron. Lett., vol. 31, no. 3, pp. 216–217, Feb. 1995. [2] N. J. Smith, F. M. Knox, N. J. Doran, K. J. Blow, and I. Bennion, “Enhanced power solitons in optical fibers with periodic dispersion management,” Electron. Lett., vol. 32, no. 1, pp. 54–55, Jan. 1995. [3] M. Nakazawa and H. Kubota, “Nonlinear pulse transmission through an optical fiber at zero-average group velocity dispersion,” IEEE Photon. Technol. Lett., vol. 8, pp. 452–454, Mar. 1996. [4] S. Kawanishi, H. Takara, O. Kamatani, T. Morioka, and M. Saruwatari, “100 Gbit/s, 560 km optical transmission experiment with 80 km amplifier spacing employing dispersion management,” Electron Lett.,vol. 32, no. 5, pp. 470–471, Feb. 1995. [5] M. Nakazawa and H. Kubota, A. Sahara, and K. Tamura, “Marked In crease in the power margin through the use of a dispersion-allocated soliton,” IEEE Photon. Technol. Lett., vol. 8, pp. 1088–1090, Aug. 1996. [6] F. M. Knox, W. Forysiak, and N. J. Doran, “10-Gbit/s soliton communication over standard fiber at 1.55 m, and the use of dispersion compensation,” J. Lightwave Technol., vol. 13, pp. 1955–1962, Oct., 1995. [7] M. Suzuki, I. Morita, S. Yamamoto, N. Edagawa, H. Taga, and S. Akiba, “Timing jitter reduction by periodic dispersion compensation in soliton transmission,” presented at OFC’95, San Diego, CA, Mar. 1995, paper PDP 20. [8] P. Delavaux, O. Mizuhara, P. D. Yeates, and T. V. Nguyen, “10 Gbit/s 150 km bi-directional repeaterless optical fiber transmission,” IEEE Photon. Technol. Lett., vol. 7, pp. 1087–1089, Sept. 1995.
