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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 18 — Sep. 3, 2007
  • pp: 11142–11153
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Performance comparison of 40 Gb/s ULH transmissions using CSRZ-ASK or CSRZ-DPSK modulation formats on UltraWave™ fiber

E. Pincemin, A. Tan, A. Tonello, S. Wabnitz, J.D. Ania-Castañón, V. Mezentsev, S. Turitsyn, Y. Jaouën, and L. Grüner-Nielsen  »View Author Affiliations


Optics Express, Vol. 15, Issue 18, pp. 11142-11153 (2007)
http://dx.doi.org/10.1364/OE.15.011142


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Abstract

In this work we present extensive comparisons between numerical modelling and experimental measurements of the transmission performance of either CSRZ-ASK or CSRZ-DPSK modulation formats for 40-Gb/s WDM ULH systems on UltraWaveTM fiber spans with all-Raman amplification. We numerically optimised the amplification and the signal format parameters for both CSRZ-DPSK and CSRZ-ASK formats. Numerical and experimental results show that, in a properly optimized transmission link, the DPSK format permits to double the transmission distance (for a given BER level) with respect to the ASK format, while keeping a substantial OSNR margin (on ASK modulation) after the propagation in the fiber line. Our comparison between numerical and experimental results permits to identify what is the most suitable BER estimator in assessing the transmission performance when using the DPSK format.

© 2007 Optical Society of America

1. Introduction

In spite of their availability since a few years as commercial products, 40 Gb/s optical transmission systems have not yet been extensively deployed in the field by carriers [1

1. “Mintera achieves record ultra long haul transmission distance at 40 Gb/s”, March 2002; “Migrating to 40-Gbit/sec DWDM networks,” FibreSystems Europe, September 2002, www.mintera.com.

3

3. “Lambdaxtreme Transport successfully completes field trial in Deutsche Telekom network,” Lucent press release, July 2002, www.lucent.com.

]. The main reason for this delay was the competition from ultra long-haul (ULH) 10 Gb/s WDM transmission systems, whose mature technology enabled maximum transmission distances well beyond 2000 km, without electronic regeneration [4

4. “CoreStream Agility Optical Transport system data sheet,” January 2007, www.ciena.com.

5

5. “Alcatel 1626 Light Manager data sheet,” January 2007, www.alcatel-lucent.com.

]. At present however there is a renewed interest in the deployment of 40 Gb/s transport solutions, thanks to transponder technology advances and the associated cost reductions. As a consequence, it is expected that upgrading ULH transmission systems to a 40 Gb/s per channel granularity will enable further cost savings [6

6. “MCI, Xtera, Mintera, and Juniper Networks Show High-Bandwidth Optical Technology Capable of Reaching Farther Distances over Existing Fiber Networks,” FibreSystems Europe, December 2005, www.mintera.com.

7

7. “40G moves back onto the agenda,” FibreSystems Europe, May 2004, www.strataligtht.com.

]. A crucial issue for carriers intending to deploy 40 Gbit/s systems is to be able to perform a critical evaluation of the performances of ULH 40 Gb/s WDM transmission systems when introducing innovative fiber bases (such as the UltraWaveTM fiber), which have been specially designed for enabling 40 Gb/s transmissions on more than 2000 km [8

8. B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, “Transmission of 1.6 Tb/s (40×42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.

15

15. C. J. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. van der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, “DWDM 40G transmission over trans-Pacific distance (10,000km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100km UltraWave fiber spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD18. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD18.

], when used in combination with advanced modulation formats [8

8. B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, “Transmission of 1.6 Tb/s (40×42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.

17

17. A. H. Gnauck, G. Raybon, S. Chandrasekhar, J. Leuthold, C. Doerr, L. Stulz, A. Agarwal, S. Banerjee, D. Grosz, S. Hunsche, A. Kung, A. Marhelyuk, D. Maywar, M. Movassaghi, X. Liu, C. Xu, X. Wei, and D. M. GillA. Sawchuk, “2.5 Tb/s (64×42.7 Gb/s) transmission over 40×100 km NZDSF using RZ-DPSK format and all-Raman-amplified spans,” in Optical Fiber Communications Conference,ed., Vol. 70 of OSA Trends in Optics and Photonics (Optical Society of America, 2002), paper FC2.

, 20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

22

22. R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, “Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber,” IEEE Photon. Technol. Lett. 12, 1624–1626 (2000). [CrossRef]

].

In this work we present, we believe for the first time, a detailed numerical and experimental inter-comparison of ULH 40 Gbit/s WDM system performance, using either the CSRZ-ASK or the CSRZ-DPSK modulation format [8

8. B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, “Transmission of 1.6 Tb/s (40×42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.

17

17. A. H. Gnauck, G. Raybon, S. Chandrasekhar, J. Leuthold, C. Doerr, L. Stulz, A. Agarwal, S. Banerjee, D. Grosz, S. Hunsche, A. Kung, A. Marhelyuk, D. Maywar, M. Movassaghi, X. Liu, C. Xu, X. Wei, and D. M. GillA. Sawchuk, “2.5 Tb/s (64×42.7 Gb/s) transmission over 40×100 km NZDSF using RZ-DPSK format and all-Raman-amplified spans,” in Optical Fiber Communications Conference,ed., Vol. 70 of OSA Trends in Optics and Photonics (Optical Society of America, 2002), paper FC2.

, 20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

22

22. R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, “Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber,” IEEE Photon. Technol. Lett. 12, 1624–1626 (2000). [CrossRef]

] over exactly the same link configuration of UltraWaveTM fiber spans [8

8. B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, “Transmission of 1.6 Tb/s (40×42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.

15

15. C. J. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. van der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, “DWDM 40G transmission over trans-Pacific distance (10,000km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100km UltraWave fiber spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD18. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD18.

]. In other words, in order to ensure a fair comparison of the system performance when using the two different modulation formats, we kept unchanged throughout the experiments both the fiber base (and the dispersion map), as well as the amplifier configuration. Moreover, we guided our experiments by means of extensive numerical simulations, in order to point out the contribution of the major sources of transmission penalty, and to determine the optimal signal and link configuration. For the DPSK format, we compared the experimental bit-error-rate (BER) with the predictions of different Q-factor estimators (such as the amplitude Q-factor [25

25. D. Marcuse, “Derivation of analytical expressions for the bit-error probability in lightwave systems with optical amplifiers,” J. Lightwave Technol. 8, 1816–1823 (1990). [CrossRef]

26

26. P. A. Humblet and M. Azizoglu, “On the bit error rate of lightwave systems with optical amplifiers,” J. Lightwave Technol. 9, 1576–1582 (1991). [CrossRef]

], the differential-phase Q-factor [20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

], as well as the semi-stochastic BER estimation using moment generating functions and the saddle point approximation [27

27. A. Richter, I. Koltchanov, K. Kuzmin, E. Myslivets, and R. Freund, “Issues on Bit-Error Rate Estimation for Fiber-Optic Communication Systems,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, Technical Digest (CD) (Optical Society of America, 2005), paper NTuH3. http://www.opticsinfobase.org/abstract.cfm?URI=NFOEC-2005-NTuH3

28

28. M.K. Liu, A.C. Vrahas, and M.J.B. Moretti, “Saddle point bit error rate computations for optical communication systems incorporating equalizers,” IEEE Trans. Commun. 43, 989–1000 (1995). [CrossRef]

]). In this way, we could determine which BER estimator is best suited to predict the experimentally observed BER, as well as the optimal system configuration. Transmission losses were compensated by bi-directional all-Raman distributed amplification: the corresponding optimal amplifier configuration (i.e., the ratio between forward and backward Raman gain) was determined by means of the nonlinearity management approach [18

18. J.D. Ania-Castañón, I.O. Nasieva, N. Kurukitkoson, S.K. Turitsyn, C. Borsier, and E. Pincemin, “Nonlinearity management in fiber transmission systems with hybrid amplification,” Opt. Commun.233, 353(2004). [CrossRef]

]. On the other hand, for each modulation format we independently optimized the span input power per channel, as well as the pre- and the post-compensation: as we shall see, the numerical and experimental optimization results are in good agreement.

2. Experimental set-up

Our experimental set-up is shown in Fig. 1. The transmitter involved sixteen DFB laser sources, ranging from 1544.53 nm to 1556.56 nm on a 100-GHz ITU-grid. Odd and even channels were separately multiplexed, independently modulated, combined and co-polarized through a polarization maintaining 3-dB coupler. Each transmitter was composed of two cascaded external LiNbO 3 Mach-Zehnder modulators.

The first modulator was used for either amplitude or phase modulation, when biased at the transmission mid or null-point, respectively. This modulator was driven by a 40-Gb/s pseudo-random bit sequence (PRBS) of 231-1 bit length. The second modulator was biased at the transmission null-point, and it was driven by a 20 GHz clock for generating the 40-GHz RZ train with a 66% duty cycle. The different WDM channels were transmitted through a pre-compensation fiber, amplified by an Erbium-doped fiber amplifier (EDFA), and injected into the loop.

Fig 1. Schematic of the experimental set-up.

In Fig. 2 we illustrate the temporal and spectral properties of our transmitter for each of the two modulation formats under test. In the left column of Fig. 2 we show the eye diagrams as measured by means of an oscilloscope equipped with a 65 GHz optical sampling module and a high-precision time base. In the right column of Fig. 2 we show the signal optical spectra from an optical spectrum analyser with 10 pm resolution bandwidth. The small residual carrier in the CSRZ-ASK spectrum of Fig. 2 is due to the imperfect modulator response.

Fig 2. Temporal and spectral characterization of our transmitters: CSRZ-ASK (top), CSRZ-DPSK (bottom).

As shown in Fig.1, the re-circulating loop contained four 100-km dispersion-managed fiber (DMF) spans of SLA-IDF-SLA UltraWaveTM fiber [8

8. B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, “Transmission of 1.6 Tb/s (40×42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.

15

15. C. J. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. van der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, “DWDM 40G transmission over trans-Pacific distance (10,000km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100km UltraWave fiber spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD18. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD18.

]. The SLA and IDF fibers at 1550 nm had a loss of 0.18 and 0.235 dB/km, a chromatic dispersion of 20 and -40 ps/nm/km, and an effective area of 107 and 31 µm2, respectively [19

19. A. Judy, “Dispersion Managed Spans in Terrestrial Routes: Technical Advantages and Practical Considerations,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper TuS1. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-TuS1

]. Each span involved a symmetrical fiber arrangement, namely: 34 km of SLA, 32 km of IDF, and 34 km of SLA. Figure 3 illustrates the details of the dispersion map over the two first circulations in the loop. The residual span cumulated dispersion was of about 40 ps/nm at 1550 nm. Therefore we inserted after the four transmission spans an additional 3.5 km of IDF, in order to bring back the loop cumulated dispersion to ~0 ps/nm. Note that the experimental loop cumulated dispersion was affected by contributions from the different devices. Therefore it was necessary to accurately measure the residual loop cumulated dispersion by means of a custom designed set-up [29

29. “CHROMOS11 optical network chromatic dispersion and PMD test set data sheet,” September 2005, www.pefiberoptics.com.

], yielding the value of 40 ps/nm. The dispersion measurement set-up implemented the differential phase shift method, where a monochromatic tuneable light source is used as transmitter. The same measurement set-up (using this time the fixed analyser method) also permitted us to determine the net polarization mode dispersion (PMD) (or average differential group delay (DGD)) in the loop. We obtained a loop PMD value close to 1 ps, whereas the nominal span PMD was equal to 0.04 ps/km1/2. In order to minimize the loop-induced polarization effects, we used a polarisation scrambler, which was synchronously modulated with the loop circulation period. The cumulated loss of each fiber span of 22.5 dB (including splices, pump-signal WDM multiplexers and connectors) was fully compensated by means of bi-directional distributed Raman amplification.

Fig 3. Left: Dispersion map on the first two loop round-trips for the channel at 1550 nm. Right: Theoretical nonlinear phase shift versus the ratio of backward to total Raman gain.

After a pre-determined number of circulations, the channel under measurement was selected by means of a square flat-top optical filter with the 20-dB bandwidth of 0.7 nm. The optimization of the filter bandwidth was performed in back-to-back configuration, and led to the same results for both the CSRZ-ASK and the CSRZ-DPSK modulation formats. The value of post-compensation was also optimized by means of a tuneable dispersion compensation module (TDCM) for each configuration under test [19

19. A. Judy, “Dispersion Managed Spans in Terrestrial Routes: Technical Advantages and Practical Considerations,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper TuS1. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-TuS1

]. Finally, the CSRZ-ASK signal was detected by a PIN photodiode and fed into a 40-Gb/s 1:4 electrical time division de-multiplexer (ETDM). For the DPSK format, before detection, the optical signal was demodulated by a Mach-Zehnder 1-bit delayed fiber interferometer (MZDI). A balanced PIN photodiode circuit acted as the DPSK detector. After the ETDM, the average BER of the four 10-Gb/s tributaries was determined. Indeed, due to the loop operation, the BER was randomly measured on each of the four 10 Gb/s tributaries, for every signal burst that was sent to the BER tester.

3. Simulation results

Next, Fig. 5 shows the dependence of the output Q factor (as in Fig. 4, the Q factor is evaluated for the central channel when propagating a comb of 5 WDM channels with 100 GHz spacing) as a function of pre-compensation and input channel power in the UltraWaveTM fiber spans. In the simulations of Fig. 5, we fixed the value of the residual loop dispersion to 40 ps/nm, which again corresponds to the measured value in our experimental setup. The white dots in the plots of Fig. 5 indicate the experimental optimal working points. Figure 5 shows that, for both the ASK and the DPSK modulation formats, the simulations predict optimal pre-compensation and channel input powers which turn out to be in good quantitative agreement with the corresponding experimental optimal values. In the simulations leading to Fig. 4 and 5, the optimization of the dispersion map and of the CSRZ-DPSK signal power was based on the evaluation of Personick’s signal quality Q factor as it is measured by a balanced detector. On the other hand, the experimental optimization of the CSRZ-DPSK transmissions was carried out by minimizing the bit-error-rate (BER) at the balanced receiver. As it is well known, with the DPSK format the simple relationship BER=(1/2)Erfc[Q√2] does not hold between the value of Q and the corresponding BER [27

27. A. Richter, I. Koltchanov, K. Kuzmin, E. Myslivets, and R. Freund, “Issues on Bit-Error Rate Estimation for Fiber-Optic Communication Systems,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, Technical Digest (CD) (Optical Society of America, 2005), paper NTuH3. http://www.opticsinfobase.org/abstract.cfm?URI=NFOEC-2005-NTuH3

].

Fig 4. Left: numerical estimation of the output Q factor [dB] as a function of the pre-compensation and of the residual loop dispersion for a transmission over 2000 km using the CSRZ-ASK format. Right: case of the CSRZ-DPSK format for a transmission over 4000 km. The input power per channel is equal to -3 dBm.
Fig 5. Left: numerical estimation of the output Q factor [dB] at 2000 km as a function of the pre-compensation and per-channel input power for CSRZ-ASK format transmission. Right: output Q factor at 4000 km for the CSRZ-DPSK format transmission.

Fig 6. Comparisons of BER predictions (versus received OSNR in 1 nm after a 4000 km UltraWaveTM link) and experiments for the CSRZ-DPSK format. △ Numerical BER from the Q factor; ◦: BER from experiments; ▫: BER from semi-analytical approach; ∙ BER from differential phase Q. Insets: phasor diagrams (optical field) for input channel powers of either - 6 dBm (left plot) or 0 dBm (right plot).

Next, we evaluated the Personick’s amplitude Q factor at the output of a balanced receiver with both our own receiver module and with the corresponding VPI receiver module. In both cases, we obtained (via the Q factor and the hypothesis of a Gaussian pdf for the electrical current fluctuations) virtually the same BER estimate as a function of the output OSNR: this estimate is shown in Fig. 6 by the open triangles, joined by a violet solid curve. Finally, we also computed the differential phase Q factor, which is obtained as discussed in reference [20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

] from mean values and standard deviations of the phases of the optical pulses (see filled black circles joined by a black solid curve in Fig. 6). By comparing all curves in Fig. 6, it is clear that the direct BER calculation based on moment generating functions and the saddle point approximation compares much better with the measured BER (both in terms of the absolute BER values for all OSNRs, as well as in terms of the selection of the optimum output OSNR ~11.8 dB value) than the BER estimation based on the different Q factors. Indeed, the BER estimation based on the amplitude Q factor results in a minimum BER (or maximum Q value) for the output OSNR value of 12.5 dB, i.e., the Q factor estimation differs by 0.7 dB from the experimentally determined value. On the other hand, Fig. 6 shows that the differential phase Q factor leads to a significant under-estimation (by about 2 dB) of the optimal receiver OSNR. Note that in our numerical simulations we neglected, besides receiver electrical noise, the presence of both PMD and gain equalizers. We believe that neglecting these impairments explains the observed difference between numerical best fit (empty squares) and the experimental (empty circles) BER curves as shown in Fig. 6. Nevertheless, the results of Fig. 6 are important in that they show the excellent agreement between the experimental and numerical best-fit optimal OSNR value. Moreover, Fig. 6 also shows that a relatively good agreement exists between the predicted and the actual observed BER values when the semi-analytical direct BER estimation is carried out at the receiver. As a final remark, the phasor plots which are shown in the insets of Fig. 6 reveal that, in the case of the CSRZ-DPSK modulation format, nonlinear phase noise is the main source of penalty for input powers above -1 dBm/ch, that is for OSNR values (1 nm calculated after 4000 km) larger than 13.5 dB.

4. Experimental results and discussion

The experimental optimization of the transmission performance involved the determination of the best pre-compensation, span input power per channel and post-compensation for the two modulation formats under study. As suggested by the numerical simulations, the optimal percentage of total span gain from either forward or backward Raman gains was fixed in the experiments to 20%–80%, and it was kept unchanged when using either the CSRZ-ASK or the CSRZ-DPSK format. Figures 7 and 8 summarise the results of our experimental optimizations. In Fig. 7(a) we show the measured BER for the central channel at 1550 nm, versus pre-compensation. The measurements were taken at 2000 km for the CSRZ-ASK format and at 4000 km for the CSRZ-DPSK format. In Fig. 7(b) we display the central channel BER versus its residual chromatic dispersion for the two modulation formats, when measured at the same transmission distances as in Fig. 7(a). Note that in Fig. 7 we used a spline fit to join the experimental points as a guide to the eye.

Fig 7. (a) BER versus pre-compensation at 2000 km for CSRZ-ASK and at 4000 km for CSRZ-DPSK for the central channel at 1550 nm, (b) BER versus residual chromatic dispersion of the central channel at 1550 nm at 2000 km for CSRZ-ASK and at 4000 km for CSRZ-DPSK.

From the observations of Fig. 7(a), one may notice that the same optimal pre-compensation of -350 ps/nm holds for both the CSRZ-ASK and CSRZ-DPSK modulation formats. Note that in the measurements of Fig.7(a) and (b) the span input power per channel was kept fixed to -5 dBm for the CSRZ-ASK format and to -3 dBm for the CSRZ-DPSK format. The results of Fig. 7(a) also show that the observed optimal negative values of pre-compensation are in good agreement with the simulation predictions of Fig. 4. On the other hand, Fig. 7(b) shows that it is necessary to accurately adjust the post-compensation in order to improve the transmission performance for the central channel by means of a proper control of the residual chromatic dispersion (with the pre-compensation fixed to -350 ps/nm). We achieved this optimal post-compensation by means of our TDCM. Figure 7(b) shows that the optimal residual dispersion for the central channel remains close to 0 ps/nm: in particular, the residual dispersion is slightly positive (+25 ps/nm) for the CSRZ-DPSK format, and it is slightly negative (-15 ps/nm) for the CSRZ-ASK format. In the following, we kept fixed the pre-compensation at its optimal value of -350 ps/nm for both modulation formats.

Figures 8(a) and (b) show the output BER as a function of the span input power per channel for the CSRZ-ASK and the CSRZ-DPSK formats. The BER was measured at various transmission distances (as indicated on the plots of Fig. 8(a) and (b)). As it can be seen in Fig.(8), at 4000 km with the CSRZ-DPSK format the optimal span input power is about 2 dB larger than at 2000 km with the CSRZ-ASK format (i.e., -3 dBm against -5 dBm); whereas the BER is nearly the same (~10-7) in the two cases. We may also observe from Fig. 8(a) that the optimal span input signal power with the CSRZ-ASK format significantly changes with the transmission distance.

Fig 8. (a) BER versus span input power of the central channel at 1550 nm at different transmission distances for CSRZ-ASK, (b) BER versus span input power of the central channel at 1550 nm at different transmission distances for CSRZ-DPSK.

Indeed, the optimal input power with the CSRZ-ASK decreases by about 1 dB per additional signal circulation through the loop. On the other hand, Fig. 8(b) shows that, when using the CSRZ-DPSK format, the transmission distance dependence of the optimal span input power per channel is significantly reduced. These measurements confirm that the CSRZ-ASK modulation format is largely more sensitive to the accumulation of nonlinear impairments than CSRZ-DPSK [20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

22

22. R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, “Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber,” IEEE Photon. Technol. Lett. 12, 1624–1626 (2000). [CrossRef]

]. Indeed, it is well known that the main sources of nonlinear degradation for pulse-overlapped 40 Gb/s optical transmissions are intra-channel cross-phase modulation (IXPM) and intra-channel four-wave mixing (IFWM). In ASK transmission, IXPM and IFWM lead to pulse timing and amplitude jitters for the marks, and to “ghost” pulse generation in the spaces [22

22. R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, “Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber,” IEEE Photon. Technol. Lett. 12, 1624–1626 (2000). [CrossRef]

]. It is also established that a symmetric dispersion map (as the one which is implemented in the present experiments) significantly improves the performance of ASK-based transmissions [23

23. E. Pincemin, D. Grot, C. Borsier, J.D. Ania-Castañòn, and S.K. Turitsyn, “Impact of the fiber type and dispersion management on the performance of an NRZ 16x40 Gb/s DWDM transmission system,” IEEE Photon. Technol. Lett. 16, 2362–2364 (2004). [CrossRef]

], by limiting the impact of both IXPM and IFWM. Nonetheless, when using the DPSK format over the same symmetric dispersion map, one obtains a net reduction of the overall intra-channel nonlinear impairments as compared with the ASK format. First of all, it is clear that for a given level of the signal average power the pulse peak power with the DPSK format is twice lower than with the ASK format. Moreover, the Gordon-Mollenauer effect [24

24. J. P. Gordon and L. F. Mollenauer, “Phase noise in photonics communications systems using linear amplifier,” Opt. Lett. 15, 1351–1355 (1990). [CrossRef] [PubMed]

] which is responsible for a detrimental nonlinear phase noise with the DPSK format, may be highly reduced in a pulse-overlapped 40 Gb/s transmission owing to the strong impact of dispersive effects (as it is the case in the present transmission line owing to the high local dispersion of the SLA and IDF fibers). Finally, note that IFWM has only limited influence on DPSK transmissions: indeed the IFWM-induced nonlinear phase noise leads to a correlation between the nonlinear phase shifts that are experienced by any two adjacent bits [20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

21

21. X. Wei and X. Liu, “Analysis of intrachannel four-wave mixing in differential phase-shift keying transmission with large dispersion,” Opt. Lett. 28, 2300–2302 (2003). [CrossRef] [PubMed]

]. Clearly this does not affect the information which is contained, for the DPSK format, in the relative phase difference between bits [20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

21

21. X. Wei and X. Liu, “Analysis of intrachannel four-wave mixing in differential phase-shift keying transmission with large dispersion,” Opt. Lett. 28, 2300–2302 (2003). [CrossRef] [PubMed]

]. Figure 9(a) shows the measured dependence of the output OSNR (measured for the central channel in 1 nm) and BER versus the transmission distance for both the CSRZ-ASK and the CSRZ-DPSK formats. In these measurements, for each transmission distance we adjusted the span input power and the post-compensation to their optimal values. On the other hand, in Fig. 9(a) the pre-compensation was not changed with respect to the value that was previously obtained by optimising the transmission performance as in Fig. 7(a) (at 2000 km for the CSRZ-ASK and at 4000 km for the CSRZ-DPSK format). As it can be seen in Fig. 9(a), for a given level of the output BER, the DPSK format enables a dramatic increase of the transmission distance with respect to the ASK format. Namely, for a BER=10-10 the transmission distance grows from 800 km (with the ASK) up to 2400 km (with the DPSK). For a BER=10-9 one obtains 1200 km with the ASK format and 3200 km with the DPSK format.

Fig 9. (a) BER and OSNR of the central channel at 1550 nm versus transmission distance for CSRZ-ASK and CSRZ-DPSK, (b) BER versus OSNR of the central channel at 1550 nm after 2000 km for CSRZ-ASK (filled purple lozenges) and after 4000 km for CSRZ-DPSK (empty red triangles) and in back-to-back for the both modulation formats (filled purple circles for CSRZ-ASK and empty red circles for CSRZ-DPSK).

For a BER=10-8, Fig. 9(a) shows that one obtains 1600 km with the ASK and 3600 km with the DPSK. Finally, for a BER=10-7, we obtain a transmission distance of 2000 km with the ASK and of 4000 km with the DPSK format, respectively; that is, in this case the CSRZ-DPSK modulation format permits to double the transmission distance when compared with CSRZ-ASK. Figure 9(a) also shows that the output OSNR is equal to 13.8 dB at 2000 km (for the ASK format) and to 11.3 dB at 4000 km for the DPSK format, respectively. Although the output OSNR is 2.5 dB lower with the CSRZ-DPSK format at 4000 km when compared with the case of the ASK format at 2000 km, nevertheless one obtains the same BER performance (10-7) in the two cases. The superior behaviour of the DPSK format can be mostly ascribed to its well-known 2.5–3 dB improvement in receiver sensitivity with respect to the ASK format (such improvement was clearly observed on the back-to-back sensitivity curves as shown in Fig. 9(b)). Additionally, as discussed above the resilience of the DPSK format to nonlinear impairments is higher than that of the ASK format [20

20. C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

21

21. X. Wei and X. Liu, “Analysis of intrachannel four-wave mixing in differential phase-shift keying transmission with large dispersion,” Opt. Lett. 28, 2300–2302 (2003). [CrossRef] [PubMed]

]. Let us point out that the results of the experimental optimization fit well the numerical results that we described in section 3: for both the ASK and the DPSK modulation formats, numerical predictions agree well with experimental optimal span input power per channel values. At last, note that the BER level (=10-7) which is obtained at 2000 km and 4000 km (for the CSRZ-ASK and the CSRZ-DPSK formats, respectively) is well below the threshold for error-free operation of forward error correction codes (which is in the BER range of [1.10-3-4.10-3], depending of the equipment supplier which is considered), proving that on UltraWave fiber both CSRZ-ASK and CSRZ-DPSK modulation formats respond to the requirement of carriers’ core transport network for ULH transmissions reaching more than 2000 km.

In Fig. 9(b) we show the results of the comparison of the dependence of the output BER upon the received OSNR for both the ASK and the DPSK formats. The OSNR was measured in 1 nm for the central channel at 1550 nm, both in back-to-back and after transmission (over 4000 km for the CSRZ-DPSK and 2000 km for the CSRZ-ASK format, respectively). Clearly, the received OSNR is a monotonic increasing function of the span input power. Therefore, qualitatively similar plots to those in Fig. 9(b) result when one displays the output BER versus the span input power per channel. However, the advantage of showing the dependence of the ouput BER versus the received OSNR is that one may directly read from the plot of Fig. 9(b) the OSNR transmission penalty, by simply comparing the back-to-back OSNR value with that obtained after the transmission (for the same level of BER). The BER versus OSNR curves in Fig. 9(b) that are obtained after transmission clearly show that at low OSNRs (or, equivalently, low span input powers) the accumulated amplified spontaneous emission (ASE) noise sets the limit to the transmission performance. Whereas the same curves in Fig. 9(b) also show that at high OSNRs the transmission quality is mostly deteriorated by nonlinear impairments. Clearly, the optimal working point (and minimum BER level) is obtained when ASE and nonlinearities contribute to transmission penalties in equal manner. By comparing in Fig. 9(b) the back-to-back BER curves with those obtained after transmission, one obtains that, at the above discussed optimal working point (i.e., OSNR value that yields minimum BER, which in the case of Fig. 9(b) is equal to 10-7 for both modulation formats), the OSNR penalty is equal to 1 dB at 4000 km for the CSRZ-DPSK format, and to 2 dB at 2000 km for the CSRZ-ASK format. Namely, with the DPSK format we observed 1dB of transmission impairment reduction with respect to the ASK case, in spite of the doubled transmission distance. It is interesting to note that the well-known ~2.5 dB OSNR sensitivity difference between the CSRZ-ASK and the CSRZ-DPSK modulation formats that is obtained in back-to-back (at the BER level of 10-7) is maintained nearly unchanged after signal transmission over either 2000 km or 4000 km, respectively. Note finally that we measured the BER of all the sixteen channels in both transmission configurations (i.e., CSRZ-ASK over 2000 km and CSRZ-DPSK over 4000 km). The resulting observed BER for all these channels was varying within 1 decade around the BER value that we obtained for the central channel.

5. Conclusion

Acknowledgments

The authors want to acknowledge particularly OFS Fitel for loaning us the UltraWaveTM fiber and J. Steenstrup for his kind support.

References and links

1.

“Mintera achieves record ultra long haul transmission distance at 40 Gb/s”, March 2002; “Migrating to 40-Gbit/sec DWDM networks,” FibreSystems Europe, September 2002, www.mintera.com.

2.

“Lucent Technologies ships its new, industry-leading optical system - LambdaXtremetransport - to Deutsche Telekom,” Lucent press release, March 2002, www.lucent.com

3.

“Lambdaxtreme Transport successfully completes field trial in Deutsche Telekom network,” Lucent press release, July 2002, www.lucent.com.

4.

“CoreStream Agility Optical Transport system data sheet,” January 2007, www.ciena.com.

5.

“Alcatel 1626 Light Manager data sheet,” January 2007, www.alcatel-lucent.com.

6.

“MCI, Xtera, Mintera, and Juniper Networks Show High-Bandwidth Optical Technology Capable of Reaching Farther Distances over Existing Fiber Networks,” FibreSystems Europe, December 2005, www.mintera.com.

7.

“40G moves back onto the agenda,” FibreSystems Europe, May 2004, www.strataligtht.com.

8.

B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, “Transmission of 1.6 Tb/s (40×42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.

9.

B. Zhu, L. Nelson, L. Leng, S. Stulz, S. Knudsen, and D. Peckham, “1.6 Tb/s (40×42.7 Gb/s) transmission over 2400 km of fibre with 100-km dispersion-managed spans,” Electron. Lett. 38, 647–648 (2002). [CrossRef]

10.

C. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. Van Der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, “DWDM 40 Gb/s Transmission over Transpacific distance (10000 km) using CSRZ-DPSK, enhanced FEC, and All-Raman amplified 100-km Ultrawave fiber spans,” J. Lightwave Technol. 10, 281–293 (2004).

11.

B. Zhu, L. E. Nelson, S. Stulz, A. H. Gnauck, C. Doerr, J. Leuthold, L. Gruner-Nielsen, M. O. Pedersen, J. Kim, R. Lingle, Y. Emori, Y. Ohki, N. Tsukiji, A. Oguri, and S. Namiki, “6.4-Tb/s (160×42.7 Gb/s) transmission with 0.8 bit/s/Hz spectral efficiency over 32×100 km of fiber using CSRZ-DPSK format,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD19. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD19.

12.

T. Tsuritani, K. Ishida, A. Agata, K. Shimomura, I. Morita, T. Tokura, H. Taga, T. Mizuochi, and N. Edagawa, “70GHz-spaced 40 x 42.7Gbit/s transmission over 8700km using CS-RZ DPSK signal, all-Raman repeaters and symmetrically dispersion-managed fiber span,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD23. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD23.

13.

B. Zhu, L. Leng, A. H. Gnauck, M. O. Pedersen, D. Peckham, L. E. Nelson, S. Stulz, S. Kado, L. Grüner-Nielsen, R. L. Lingle, S. Knudsen, C. Leuthold, S. Doerr, G. Chandrasekhar, P. Baynham, Y. Gaarde, S. Emori, and Namiki, “Transmission of 3.2 Tb/s (80×42.7 Gb/s) over 5200 km of UltraWave fiber with 100-km dispersion managed spans using RZ-DPSK format,” in proceedings ECOC’2002, DK, Copenhaguen, paper PD4.2.

14.

C. Rasmussen, S. Dey, F. Liu, J. Bennike, B. Mikkelsen, P. Mamyshev, M. Kimmitt, K. Springer, D. Gapontsev, and V. Ivshin, “Transmission of 40×42.7 Gb/s over 5200 km ultraWave fiber with terrestrial 100 km spans using turn-key ETDM transmitter and receiver,” in proceedings ECOC’2002, DK, Copenhaguen, paper PD4.4.

15.

C. J. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. van der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, “DWDM 40G transmission over trans-Pacific distance (10,000km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100km UltraWave fiber spans,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD18. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD18.

16.

T. Hoshida, O. Vassilieva, K. Yamada, S. Choudhary, R. Pecqueur, and H. Kuwahara, “Optimal 40 Gb/s modulation formats for spectrally efficient long-haul DWDM systems,” J. Lightwave Technol. 20, 1989–1996 (2002). [CrossRef]

17.

A. H. Gnauck, G. Raybon, S. Chandrasekhar, J. Leuthold, C. Doerr, L. Stulz, A. Agarwal, S. Banerjee, D. Grosz, S. Hunsche, A. Kung, A. Marhelyuk, D. Maywar, M. Movassaghi, X. Liu, C. Xu, X. Wei, and D. M. GillA. Sawchuk, “2.5 Tb/s (64×42.7 Gb/s) transmission over 40×100 km NZDSF using RZ-DPSK format and all-Raman-amplified spans,” in Optical Fiber Communications Conference,ed., Vol. 70 of OSA Trends in Optics and Photonics (Optical Society of America, 2002), paper FC2.

18.

J.D. Ania-Castañón, I.O. Nasieva, N. Kurukitkoson, S.K. Turitsyn, C. Borsier, and E. Pincemin, “Nonlinearity management in fiber transmission systems with hybrid amplification,” Opt. Commun.233, 353(2004). [CrossRef]

19.

A. Judy, “Dispersion Managed Spans in Terrestrial Routes: Technical Advantages and Practical Considerations,” in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper TuS1. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-TuS1

20.

C. Xu, X. Liu, and X. Wei, “DPSK for high spectral efficiency optical transmissions,” J. Selected Topics Quantum Electron. 10, 281–293 (2004). [CrossRef]

21.

X. Wei and X. Liu, “Analysis of intrachannel four-wave mixing in differential phase-shift keying transmission with large dispersion,” Opt. Lett. 28, 2300–2302 (2003). [CrossRef] [PubMed]

22.

R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, “Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber,” IEEE Photon. Technol. Lett. 12, 1624–1626 (2000). [CrossRef]

23.

E. Pincemin, D. Grot, C. Borsier, J.D. Ania-Castañòn, and S.K. Turitsyn, “Impact of the fiber type and dispersion management on the performance of an NRZ 16x40 Gb/s DWDM transmission system,” IEEE Photon. Technol. Lett. 16, 2362–2364 (2004). [CrossRef]

24.

J. P. Gordon and L. F. Mollenauer, “Phase noise in photonics communications systems using linear amplifier,” Opt. Lett. 15, 1351–1355 (1990). [CrossRef] [PubMed]

25.

D. Marcuse, “Derivation of analytical expressions for the bit-error probability in lightwave systems with optical amplifiers,” J. Lightwave Technol. 8, 1816–1823 (1990). [CrossRef]

26.

P. A. Humblet and M. Azizoglu, “On the bit error rate of lightwave systems with optical amplifiers,” J. Lightwave Technol. 9, 1576–1582 (1991). [CrossRef]

27.

A. Richter, I. Koltchanov, K. Kuzmin, E. Myslivets, and R. Freund, “Issues on Bit-Error Rate Estimation for Fiber-Optic Communication Systems,” in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, Technical Digest (CD) (Optical Society of America, 2005), paper NTuH3. http://www.opticsinfobase.org/abstract.cfm?URI=NFOEC-2005-NTuH3

28.

M.K. Liu, A.C. Vrahas, and M.J.B. Moretti, “Saddle point bit error rate computations for optical communication systems incorporating equalizers,” IEEE Trans. Commun. 43, 989–1000 (1995). [CrossRef]

29.

“CHROMOS11 optical network chromatic dispersion and PMD test set data sheet,” September 2005, www.pefiberoptics.com.

OCIS Codes
(060.4080) Fiber optics and optical communications : Modulation
(060.4510) Fiber optics and optical communications : Optical communications
(190.4370) Nonlinear optics : Nonlinear optics, fibers

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: April 24, 2007
Revised Manuscript: July 4, 2007
Manuscript Accepted: July 15, 2007
Published: August 21, 2007

Citation
E. Pincemin, A. Tan, A. Tonello, S. Wabnitz, J.D. Ania-Castañòn, V. Mezenstev, S. Turitsyn, Y. Jaouën, and L. Grüner-Nielsen, "Performance comparison of 40 Gb/s ULH transmissions using CSRZ-ASK or CSRZ-DPSK modulation formats on UltraWave fiber TM fiber," Opt. Express 15, 11142-11153 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-18-11142


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References

  1. Mintera achieves record ultra long haul transmission distance at 40 Gb/s", March 2002; "Migrating to 40-Gbit/sec DWDM networks," FibreSystems Europe, September 2002, www.mintera.com.
  2. "Lucent Technologies ships its new, industry-leading optical system - LambdaXtreme™ transport - to Deutsche Telekom," Lucent press release, March 2002, www.lucent.com
  3. "Lambdaxtreme™ Transport successfully completes field trial in Deutsche Telekom network," Lucent press release, July 2002, www.lucent.com.
  4. "CoreStream Agility Optical Transport system data sheet," January 2007, www.ciena.com.
  5. "Alcatel 1626 Light Manager data sheet," January 2007, www.alcatel-lucent.com.
  6. "MCI, Xtera, Mintera, and Juniper Networks Show High-Bandwidth Optical Technology Capable of Reaching Farther Distances over Existing Fiber Networks," FibreSystems Europe, December 2005, www.mintera.com.
  7. "40G moves back onto the agenda," FibreSystems Europe, May 2004, www.strataligtht.com.
  8. B. Zhu, L. E. Nelson, L. Leng, M. O. Pedersen, D. W. Peckham, and S. L. Stulz, "Transmission of 1.6 Tb/s (40 x 42.7 Gb/s) Over Transoceanic Distance with Terrestrial 100-km Amplifier Spans," in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper FN2. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-FN2.
  9. B. Zhu, L. Nelson, L. Leng, S. Stulz, S. Knudsen, and D. Peckham, " 1.6 Tb/s (40 x 42.7 Gb/s) transmission over 2400 km of fibre with 100-km dispersion-managed spans," Electron. Lett. 38, 647-648 (2002). [CrossRef]
  10. C. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. Van Der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, "DWDM 40 Gb/s Transmission over Transpacific distance (10000 km) using CSRZ-DPSK, enhanced FEC, and All-Raman amplified 100-km Ultrawave fiber spans," J. Lightwave Technol. 10, 281-293 (2004).
  11. B. Zhu, L. E. Nelson, S. Stulz, A. H. Gnauck, C. Doerr, J. Leuthold, L. Gruner-Nielsen, M. O. Pedersen, J. Kim, R. Lingle, Y. Emori, Y. Ohki, N. Tsukiji, A. Oguri, and S. Namiki, "6.4-Tb/s (160 x 42.7 Gb/s) transmission with 0.8 bit/s/Hz spectral efficiency over 32 x 100 km of fiber using CSRZ-DPSK format," in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD19. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD19.
  12. T. Tsuritani, K. Ishida, A. Agata, K. Shimomura, I. Morita, T. Tokura, H. Taga, T. Mizuochi, and N. Edagawa, "70GHz-spaced 40 x 42.7Gbit/s transmission over 8700km using CS-RZ DPSK signal, all-Raman repeaters and symmetrically dispersion-managed fiber span," in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD23. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD23.
  13. B. Zhu, L. Leng, A. H. Gnauck, M. O. Pedersen, D. Peckham, L. E. Nelson, S. Stulz, S. Kado, L. Grüner-Nielsen, R. L. Lingle, S. Knudsen, J. Leuthold, C. Doerr, S. Chandrasekhar, G. Baynham, P. Gaarde, Y. Emori, and S. Namiki, "Transmission of 3.2 Tb/s (80 x 42.7 Gb/s) over 5200 km of UltraWave fiber with 100-km dispersion managed spans using RZ-DPSK format," in Proceedings ECOC '2002, DK, Copenhaguen, paper PD4.2.
  14. C. Rasmussen, S. Dey, F. Liu, J. Bennike, B. Mikkelsen, P. Mamyshev, M. Kimmitt, K. Springer, D. Gapontsev, and V. Ivshin, "Transmission of 40x42.7 Gb/s over 5200 km ultraWave fiber with terrestrial 100 km spans using turn-key ETDM transmitter and receiver," in Proceedings ECOC '2002, DK, Copenhaguen, paper PD4.4.
  15. C. J. Rasmussen, T. Fjelde, J. Bennike, F. Liu, S. Dey, B. Mikkelsen, P. Mamyshev, P. Serbe, P. van der Wagt, Y. Akasaka, D. Harris, D. Gapontsev, V. Ivshin, and P. Reeves-Hall, "DWDM 40G transmission over trans-Pacific distance (10,000km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100km UltraWave™ fiber spans," in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper PD18. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-PD18>.
  16. T. Hoshida, O. Vassilieva, K. Yamada, S. Choudhary, R. Pecqueur, and H. Kuwahara, "Optimal 40 Gb/s modulation formats for spectrally efficient long-haul DWDM systems," J. Lightwave Technol. 20, 1989-1996 (2002). [CrossRef]
  17. A. H. Gnauck, G. Raybon, S. Chandrasekhar, J. Leuthold, C. Doerr, L. Stulz, A. Agarwal, S. Banerjee, D. Grosz, S. Hunsche, A. Kung, A. Marhelyuk, D. Maywar, M. Movassaghi, X. Liu, C. Xu, X. Wei, and D. M. Gill, "2.5 Tb/s (64x42.7 Gb/s) transmission over 40x100 km NZDSF using RZ-DPSK format and all-Raman-amplified spans," in Optical Fiber Communications Conference, A. Sawchuk, ed., Vol. 70 of OSA Trends in Optics and Photonics (Optical Society of America, 2002), paper FC2.
  18. J. D. Ania-Castañón, I. O. Nasieva, N. Kurukitkoson, S. K. Turitsyn, C. Borsier, and E. Pincemin, "Nonlinearity management in fiber transmission systems with hybrid amplification," Opt. Commun. 233, 353 (2004). [CrossRef]
  19. A. Judy, "Dispersion Managed Spans in Terrestrial Routes: Technical Advantages and Practical Considerations," in Optical Fiber Communication Conference, Technical Digest (Optical Society of America, 2003), paper TuS1. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2003-TuS1
  20. C. Xu, X. Liu, and X. Wei, "DPSK for high spectral efficiency optical transmissions,"IEEE J. Sel. Top. Quantum Electron. 10, 281-293 (2004). [CrossRef]
  21. X. Wei and X. Liu, "Analysis of intrachannel four-wave mixing in differential phase-shift keying transmission with large dispersion," Opt. Lett. 28, 2300-2302 (2003). [CrossRef] [PubMed]
  22. R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, "Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber," IEEE Photon. Technol. Lett. 12, 1624-1626 (2000). [CrossRef]
  23. E. Pincemin, D. Grot, C. Borsier, J. D. Ania-Castañòn, and S. K. Turitsyn, "Impact of the fiber type and dispersion management on the performance of an NRZ 16x40 Gb/s DWDM transmission system," IEEE Photon. Technol. Lett. 16, 2362-2364 (2004). [CrossRef]
  24. J. P. Gordon and L. F. Mollenauer, "Phase noise in photonics communications systems using linear amplifier," Opt. Lett. 15, 1351-1355 (1990). [CrossRef] [PubMed]
  25. D. Marcuse, "Derivation of analytical expressions for the bit-error probability in lightwave systems with optical amplifiers," J. Lightwave Technol. 8, 1816-1823 (1990). [CrossRef]
  26. P. A. Humblet and M. Azizoglu, "On the bit error rate of lightwave systems with optical amplifiers," J. Lightwave Technol. 9, 1576-1582 (1991). [CrossRef]
  27. A. Richter, I. Koltchanov, K. Kuzmin, E. Myslivets, and R. Freund, " Issues on Bit-Error Rate Estimation for Fiber-Optic Communication Systems," in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, Technical Digest (CD) (Optical Society of America, 2005), paper NTuH3. http://www.opticsinfobase.org/abstract.cfm?URI=NFOEC-2005-NTuH3
  28. M. K. Liu, A. C. Vrahas, and M. J. B. Moretti, "Saddle point bit error rate computations for optical communication systems incorporating equalizers," IEEE Trans. Commun. 43, 989-1000 (1995). [CrossRef]
  29. "CHROMOS11 optical network chromatic dispersion and PMD test set data sheet," September 2005, www.pefiberoptics.com.

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