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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 26 — Dec. 12, 2011
  • pp: B805–B810
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Polarization multiplexed 16QAM transmission employing modified digital back-propagation

Danish Rafique, Marco Mussolin, Jonas Mårtensson, Marco Forzati, Johannes K. Fischer, Lutz Molle, Markus Nölle, Colja Schubert, and Andrew D. Ellis  »View Author Affiliations


Optics Express, Vol. 19, Issue 26, pp. B805-B810 (2011)
http://dx.doi.org/10.1364/OE.19.00B805


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Abstract

We experimentally demonstrate performance enhancements enabled by weighted digital back propagation method for 28 Gbaud PM-16QAM transmission systems, over a 250 km ultra-large area fibre, using only one back-propagation step for the entire link, enabling up to 3 dB improvement in power tolerance with respect to linear compensation only. We observe that this is roughly the same improvement that can be obtained with the conventional, computationally heavy, non-weighted digital back propagation compensation with one step per span. As a further benchmark, we analyze performance improvement as a function of number of steps, and show that the performance improvement saturates at approximately 20 steps per span, at which a 5 dB improvement in power tolerance is obtained with respect to linear compensation only. Furthermore, we show that coarse-step self-phase modulation compensation is inefficient in wavelength division multiplexed transmission.

© 2011 OSA

1. Introduction

Exponentially growing global bandwidth demand is fueling the need to increase the capacity and spectral efficiency of the deployed wavelength-division multiplexed (WDM) optical networks [1

1. A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol. 28(4), 423–433 (2010). [CrossRef]

]. In recent years, coherent detection and digital signal processing have become the most favourable technologies to enhance the available transport capacity in optical fibre [2

2. S. J. Savory, G. Gavioli, R. I. Killey, and P. Bayvel, “Electronic compensation of chromatic dispersion using a digital coherent receiver,” Opt. Express 15(5), 2120–2126 (2007). [CrossRef] [PubMed]

]. For a further increase of channel capacity, a promising modulation format is polarization multiplexed 16-level quadrature amplitude modulation (PM-16QAM), which allows for a spectral efficiency of 4 bits/s/Hz, when transmitted at a symbol rate of 28/56 Gbaud over the 50/100 GHz channel grid [3

3. P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, and L. L. Buhl, “Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM,” J. Lightwave Technol. 28(4), 547–556 (2010). [CrossRef]

]. Nevertheless, such an increase in transmission capacity emerges at the expense of increased susceptibility to linear and nonlinear fibre impairments. As linear compensation methods have matured in the past few years [2

2. S. J. Savory, G. Gavioli, R. I. Killey, and P. Bayvel, “Electronic compensation of chromatic dispersion using a digital coherent receiver,” Opt. Express 15(5), 2120–2126 (2007). [CrossRef] [PubMed]

,4

4. C. R. S. Fludger, T. Duthel, D. van den Borne, C. Schulien, E.-D. Schmidt, T. Wuth, J. Geyer, E. De Man, G.-D. Khoe, and H. de Waardt, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightwave Technol. 26(1), 64–72 (2008). [CrossRef]

,5

5. M. Kuschnerov, F. N. Hauske, K. Piyawanno, B. Spinnler, M. S. Alfiad, A. Napoli, and B. Lankl, “DSP for coherent single-carrier receivers,” J. Lightwave Technol. 27(16), 3614–3622 (2009). [CrossRef]

], research has intensified on nonlinear impairments compensation [6

6. S. L. Jansen, D. van den Borne, B. Spinnler, S. Calabrò, H. Suche, P. M. Krummrich, W. Sohler, G.-D. Khoe, and H. de Waardt, “Optical phase conjugation for ultra long-haul phase-shift-keyed transmission,” J. Lightwave Technol. 24(1), 54–64 (2006). [CrossRef]

8

8. X. Li, X. Chen, G. Goldfarb, E. Mateo, I. Kim, F. Yaman, and G. Li, “Electronic post-compensation of WDM transmission impairments using coherent detection and digital signal processing,” Opt. Express 16(2), 880–888 (2008). [CrossRef] [PubMed]

]. In particular, electronic signal processing using digital back-propagation (DBP) has been applied to the compensation of channel nonlinearities [7

7. E. Ip, “Nonlinear compensation using backpropagation for polarization-multiplexed transmission,” J. Lightwave Technol. 28(6), 939–951 (2010). [CrossRef]

11

11. X. Chongjin and R. J. Essiambre, “Electronic nonlinearity compensation in 112-Gb/s PDM-QPSK optical coherent transmission systems,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper Mo.1.C.1.

]. However, the complexity of DBP is currently exorbitant, due to significantly high number of processing steps required in such calculations. Simplified DBP algorithms have been proposed [12

12. L. B. Du and A. J. Lowery, “Improved single channel backpropagation for intra-channel fiber nonlinearity compensation in long-haul optical communication systems,” Opt. Express 18(16), 17075–17088 (2010). [CrossRef] [PubMed]

14

14. D. Rafique, M. Mussolin, M. Forzati, J. Mårtensson, M. N. Chugtai, and A. D. Ellis, “Compensation of intra-channel nonlinear fibre impairments using simplified digital back-propagation algorithm,” Opt. Express 19(10), 9453–9460 (2011). [CrossRef] [PubMed]

] and investigated for a 14 Gbaud PM-16QAM experimental transmissions [15

15. S. Makovejs, D. S. Millar, D. Lavery, C. Behrens, R. I. Killey, S. J. Savory, and P. Bayvel, “Characterization of long-haul 112Gbit/s PDM-QAM-16 transmission with and without digital nonlinearity compensation,” Opt. Express 18(12), 12939–12947 (2010). [CrossRef] [PubMed]

].

2. Experimental setup

2.1 Transmitter (single-channel)

2.2 Transmitter (WDM)

Detailed experimental setup for 8 × 224 Gb/s PM-16QAM is reported in [16

16. J. K. Fischer, L. Molle, M. Nölle, C. Schmidt-Langhorst, J. Hilt, R. Ludwig, D. W. Peckham, and C. Schubert, “8×448 Gb/s WDM transmission of 56 GBd PDM 16-QAM OTDM signals over 250 km ultra-large effective area fiber,” IEEE Photon. Technol. Lett. 23(4), 239–241 (2011). [CrossRef]

,17

17. M. Nölle, J. Hilt, L. Molle, M. Seimetz, and R. Freund, “8×224 Gbit/s PDM 16QAM WDM transmission with real-time signal processing at the transmitter,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper We.8.C.4.

], where the transmitter configuration shown in Fig. 1 is also used in the WDM experiments at 224 Gb/s.

2.3 Receiver and digital signal processing

At the receiver, an EDFA was used as preamplifier and a variable optical attenuator (VOA) allowed for variation in received OSNR for back-to-back measurements (when the signal was transmitted over the link, this stage was removed, and OSNR was varied by varying the power launched into the fibre). After passing through the amplifier and a 10 dB coupler (for OSNR evaluation), the signal was filtered by a 0.5 nm optical filter and boosted by a second EDFA.

The signals corresponding to I and Q components of the two orthogonal polarizations were digitized in batches of 10M samples by asynchronous sampling in a real-time oscilloscope and subsequently processed in a computer. The bandwidths and sampling rates of the employed oscilloscopes were 20GHz, 50GS/s. The post-processing included several blocks (see [18

18. B. Olsson, J. Mårtensson, A. Kristiansson, and A. Alping, “RF-assisted optical dual-carrier 112 Gbit/s polarization-multiplexed 16-QAM transmitter,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OMK5.

] for more details about some of the algorithms). First sampling skew and I/Q-phase offset was corrected before upsampling to approximately 2 samples/symbol. Then either linear chromatic dispersion (CD) compensation using a static frequency domain filter, or CD and nonlinear compensation using digital back-propagation (DBP) was performed before timing recovery and resampling again to a synchronous 2 samples/symbol. Polarization demultiplexing and equalization was performed using four adaptive filters in MIMO configuration with 27 taps each. Constant modulus algorithm (CMA) was used for initial convergence before estimating and removing initial carrier frequency offset and then switching to decision-directed adaptation combined with phase-noise tolerant decision-aided carrier phase estimation. Special care is taken when calculating the decision-directed least-mean square (LMS) error in order to decouple filter tap updating from phase tracking. Finally, a number of symbols needed for convergence were discarded before mapping symbols, which were differentially coded, to bits and counting errors. About 5.5 million symbols in each polarization were used for the bit-error rate (BER) computation, which was eventually converted into Q-factor [19

19. R.-J. Essiambre, P. J. Winzer, and D. F. Grosz, “Impact of DCF properties on system design,” Opt. Fiber Commun. Rep. 5, 425–495(2007).

].

3. Results and discussions

The difference between LC and NW-DBP (20 steps per span) is qualitatively illustrated for 35 dB OSNR, in the constellation diagrams shown in Fig. 3
Fig. 3 Constellation diagrams with only (a) LC and, (b) W-DBP (1 step per link), at OSNR level of 35 dB (launch power of 9 dBm). Single channel transmission at 28 Gbaud.
. It is clear that when using LC (Fig. 3a) alone, the constellation diagrams are degraded. However, the use of DBP (Fig. 3b) enables almost noise-free identification of the mean location of individual symbols. Note that in both cases, the noise distribution looks symmetric (except for additional phase noise on outer symbols) and appear to follow bi-Gaussian distribution. We attribute the Gaussian noise distributions in this configuration to the short correlation length due to highly dispersive transmission, sufficiently randomizing the nonlinear interactions, in consistent with recently reported results [20

20. P. Poggiolini, A. Carena, V. Curri, G. Bosco, and F. Forghieri, “Analytical modeling of nonlinear propagation in uncompensated optical transmission links,” IEEE Photon. Technol. Lett. 23(11), 742–744 (2011). [CrossRef]

]. In order to identify the maximum improvement achievable with DBP, we investigated the performance of NW-DBP algorithm, increasing the number of steps per span up to 50 as shown in Fig. 4
Fig. 4 Q versus steps per span (NW-DBP case). Single channel transmission at 28 Gbaud. OSNR level of 35 dB (launch power of 9 dBm)
. The scope of improvement with W-DBP is reduced for high number of steps, so it was not analyzed. It can be seen that Q increases as a function of required number of DBP steps up until 20 steps per span (giving a power tolerance improvement of 5 dB, Fig. 2), above which it saturates.

Figure 5
Fig. 5 Q versus launch power, for 8 channel 28 Gbaud transmission over 480 km SSMF transmission with LC (squares) and NW-DBP (3 steps per link).
shows the transmission performance as a function of launch power for WDM transmission employing 28 Gbaud PM-16QAM. It can be seen that intra-channel nonlinearity compensation is inefficient. This is because inter-channel effects are sufficiently strong to modify the optical fields in such a way that individual coarse-step channel compensation is inept. Nonetheless, if DBP based on optimum step-size is employed, one may expect higher baud-rate systems to show improved performance, since relative impact of inter-channel nonlinearities reduces as the baud-rate increases [21

21. P. Poggiolini, G. Bosco, A. Carena, V. Curri, V. Miot, and F. Forghieri, “Performance dependence on channel baud-rate of PM-QPSK systems over uncompensated links,” IEEE Photon. Technol. Lett. 23(1), 15–17 (2011). [CrossRef]

].

4. Conclusions

We experimentally demonstrate the effectiveness of digital back propagation in coherently-detected 28 PM-16QAM system, over 250km of uncompensated link, and report up to 3 dB improvements in power tolerance compared to linear compensation. We show that the same improvement can be obtained using standard DBP with one step per span and with weighted DBP with one step for the whole link. This confirms that the computational burden of DBP can be greatly reduced using weighing, without compromising performance improvement significantly. We also investigated the maximum improvement achievable using non-weighted DBP with several steps per span and observed that performance improvement saturated at 20 steps per span, showing an improvement of 5 dB in launch power tolerance. We also show that in a WDM system, the coarse-step DBP approach has reduced effectiveness.

Acknowledgments

The work described in this paper was carried out with the support of the EUROFOS project, Network of Excellence funded by the European Commission through the 7th ICT-Framework Programme, and Science Foundation Ireland under Grant 06/IN/I969. The ultra-large effective area fibres were kindly provided by OFS Labs.

References and links

1.

A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol. 28(4), 423–433 (2010). [CrossRef]

2.

S. J. Savory, G. Gavioli, R. I. Killey, and P. Bayvel, “Electronic compensation of chromatic dispersion using a digital coherent receiver,” Opt. Express 15(5), 2120–2126 (2007). [CrossRef] [PubMed]

3.

P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, and L. L. Buhl, “Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM,” J. Lightwave Technol. 28(4), 547–556 (2010). [CrossRef]

4.

C. R. S. Fludger, T. Duthel, D. van den Borne, C. Schulien, E.-D. Schmidt, T. Wuth, J. Geyer, E. De Man, G.-D. Khoe, and H. de Waardt, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightwave Technol. 26(1), 64–72 (2008). [CrossRef]

5.

M. Kuschnerov, F. N. Hauske, K. Piyawanno, B. Spinnler, M. S. Alfiad, A. Napoli, and B. Lankl, “DSP for coherent single-carrier receivers,” J. Lightwave Technol. 27(16), 3614–3622 (2009). [CrossRef]

6.

S. L. Jansen, D. van den Borne, B. Spinnler, S. Calabrò, H. Suche, P. M. Krummrich, W. Sohler, G.-D. Khoe, and H. de Waardt, “Optical phase conjugation for ultra long-haul phase-shift-keyed transmission,” J. Lightwave Technol. 24(1), 54–64 (2006). [CrossRef]

7.

E. Ip, “Nonlinear compensation using backpropagation for polarization-multiplexed transmission,” J. Lightwave Technol. 28(6), 939–951 (2010). [CrossRef]

8.

X. Li, X. Chen, G. Goldfarb, E. Mateo, I. Kim, F. Yaman, and G. Li, “Electronic post-compensation of WDM transmission impairments using coherent detection and digital signal processing,” Opt. Express 16(2), 880–888 (2008). [CrossRef] [PubMed]

9.

D. Rafique, J. Zhao, and A. D. Ellis, “Impact of dispersion map management on the performance of back-propagation for nonlinear WDM transmissions,” in 2010 15th OptoeElectronics and Communications Conference (OECC), (2010), pp. 760–761

10.

S. Oda, T. Tanimura, T. Hoshida, C. Ohshima, H. Nakashima, T. Zhenning, and J. C. Rasmussen, “112 Gb/s DP-QPSK transmission using a novel nonlinear compensator in digital coherent receiver,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2009), paper OThR6.

11.

X. Chongjin and R. J. Essiambre, “Electronic nonlinearity compensation in 112-Gb/s PDM-QPSK optical coherent transmission systems,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper Mo.1.C.1.

12.

L. B. Du and A. J. Lowery, “Improved single channel backpropagation for intra-channel fiber nonlinearity compensation in long-haul optical communication systems,” Opt. Express 18(16), 17075–17088 (2010). [CrossRef] [PubMed]

13.

L. Lei, T. Zhenning, D. Liang, Y. Weizhen, O. Shoichiro, T. Takahito, H. Takeshi, and C. R. Jens, “Implementation efficient nonlinear equalizer based on correlated digital backpropagation,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OWW3.

14.

D. Rafique, M. Mussolin, M. Forzati, J. Mårtensson, M. N. Chugtai, and A. D. Ellis, “Compensation of intra-channel nonlinear fibre impairments using simplified digital back-propagation algorithm,” Opt. Express 19(10), 9453–9460 (2011). [CrossRef] [PubMed]

15.

S. Makovejs, D. S. Millar, D. Lavery, C. Behrens, R. I. Killey, S. J. Savory, and P. Bayvel, “Characterization of long-haul 112Gbit/s PDM-QAM-16 transmission with and without digital nonlinearity compensation,” Opt. Express 18(12), 12939–12947 (2010). [CrossRef] [PubMed]

16.

J. K. Fischer, L. Molle, M. Nölle, C. Schmidt-Langhorst, J. Hilt, R. Ludwig, D. W. Peckham, and C. Schubert, “8×448 Gb/s WDM transmission of 56 GBd PDM 16-QAM OTDM signals over 250 km ultra-large effective area fiber,” IEEE Photon. Technol. Lett. 23(4), 239–241 (2011). [CrossRef]

17.

M. Nölle, J. Hilt, L. Molle, M. Seimetz, and R. Freund, “8×224 Gbit/s PDM 16QAM WDM transmission with real-time signal processing at the transmitter,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper We.8.C.4.

18.

B. Olsson, J. Mårtensson, A. Kristiansson, and A. Alping, “RF-assisted optical dual-carrier 112 Gbit/s polarization-multiplexed 16-QAM transmitter,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OMK5.

19.

R.-J. Essiambre, P. J. Winzer, and D. F. Grosz, “Impact of DCF properties on system design,” Opt. Fiber Commun. Rep. 5, 425–495(2007).

20.

P. Poggiolini, A. Carena, V. Curri, G. Bosco, and F. Forghieri, “Analytical modeling of nonlinear propagation in uncompensated optical transmission links,” IEEE Photon. Technol. Lett. 23(11), 742–744 (2011). [CrossRef]

21.

P. Poggiolini, G. Bosco, A. Carena, V. Curri, V. Miot, and F. Forghieri, “Performance dependence on channel baud-rate of PM-QPSK systems over uncompensated links,” IEEE Photon. Technol. Lett. 23(1), 15–17 (2011). [CrossRef]

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2330) Fiber optics and optical communications : Fiber optics communications
(190.4370) Nonlinear optics : Nonlinear optics, fibers

ToC Category:
Transmission Systems and Network Elements

History
Original Manuscript: September 30, 2011
Revised Manuscript: November 21, 2011
Manuscript Accepted: November 25, 2011
Published: December 6, 2011

Virtual Issues
European Conference on Optical Communication 2011 (2011) Optics Express

Citation
Danish Rafique, Marco Mussolin, Jonas Mårtensson, Marco Forzati, Johannes K. Fischer, Lutz Molle, Markus Nölle, Colja Schubert, and Andrew D. Ellis, "Polarization multiplexed 16QAM transmission employing modified digital back-propagation," Opt. Express 19, B805-B810 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-26-B805


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References

  1. A. D. Ellis, J. Zhao, and D. Cotter, “Approaching the non-linear Shannon limit,” J. Lightwave Technol. 28(4), 423–433 (2010). [CrossRef]
  2. S. J. Savory, G. Gavioli, R. I. Killey, and P. Bayvel, “Electronic compensation of chromatic dispersion using a digital coherent receiver,” Opt. Express 15(5), 2120–2126 (2007). [CrossRef] [PubMed]
  3. P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, and L. L. Buhl, “Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM,” J. Lightwave Technol. 28(4), 547–556 (2010). [CrossRef]
  4. C. R. S. Fludger, T. Duthel, D. van den Borne, C. Schulien, E.-D. Schmidt, T. Wuth, J. Geyer, E. De Man, G.-D. , Khoe, and H. de Waardt, “Coherent equalization and POLMUX-RZ-DQPSK for robust 100-GE transmission,” J. Lightwave Technol. 26(1), 64–72 (2008). [CrossRef]
  5. M. Kuschnerov, F. N. Hauske, K. Piyawanno, B. Spinnler, M. S. Alfiad, A. Napoli, and B. Lankl, “DSP for coherent single-carrier receivers,” J. Lightwave Technol. 27(16), 3614–3622 (2009). [CrossRef]
  6. S. L. Jansen, D. van den Borne, B. Spinnler, S. Calabrò, H. Suche, P. M. Krummrich, W. Sohler, G.-D. Khoe, and H. de Waardt, “Optical phase conjugation for ultra long-haul phase-shift-keyed transmission,” J. Lightwave Technol. 24(1), 54–64 (2006). [CrossRef]
  7. E. Ip, “Nonlinear compensation using backpropagation for polarization-multiplexed transmission,” J. Lightwave Technol. 28(6), 939–951 (2010). [CrossRef]
  8. X. Li, X. Chen, G. Goldfarb, E. Mateo, I. Kim, F. Yaman, and G. Li, “Electronic post-compensation of WDM transmission impairments using coherent detection and digital signal processing,” Opt. Express 16(2), 880–888 (2008). [CrossRef] [PubMed]
  9. D. Rafique, J. Zhao, and A. D. Ellis, “Impact of dispersion map management on the performance of back-propagation for nonlinear WDM transmissions,” in 2010 15th OptoeElectronics and Communications Conference (OECC), (2010), pp. 760–761
  10. S. Oda, T. Tanimura, T. Hoshida, C. Ohshima, H. Nakashima, T. Zhenning, and J. C. Rasmussen, “112 Gb/s DP-QPSK transmission using a novel nonlinear compensator in digital coherent receiver,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2009), paper OThR6.
  11. X. Chongjin and R. J. Essiambre, “Electronic nonlinearity compensation in 112-Gb/s PDM-QPSK optical coherent transmission systems,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper Mo.1.C.1.
  12. L. B. Du and A. J. Lowery, “Improved single channel backpropagation for intra-channel fiber nonlinearity compensation in long-haul optical communication systems,” Opt. Express 18(16), 17075–17088 (2010). [CrossRef] [PubMed]
  13. L. Lei, T. Zhenning, D. Liang, Y. Weizhen, O. Shoichiro, T. Takahito, H. Takeshi, and C. R. Jens, “Implementation efficient nonlinear equalizer based on correlated digital backpropagation,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OWW3.
  14. D. Rafique, M. Mussolin, M. Forzati, J. Mårtensson, M. N. Chugtai, and A. D. Ellis, “Compensation of intra-channel nonlinear fibre impairments using simplified digital back-propagation algorithm,” Opt. Express 19(10), 9453–9460 (2011). [CrossRef] [PubMed]
  15. S. Makovejs, D. S. Millar, D. Lavery, C. Behrens, R. I. Killey, S. J. Savory, and P. Bayvel, “Characterization of long-haul 112Gbit/s PDM-QAM-16 transmission with and without digital nonlinearity compensation,” Opt. Express 18(12), 12939–12947 (2010). [CrossRef] [PubMed]
  16. J. K. Fischer, L. Molle, M. Nölle, C. Schmidt-Langhorst, J. Hilt, R. Ludwig, D. W. Peckham, and C. Schubert, “8×448 Gb/s WDM transmission of 56 GBd PDM 16-QAM OTDM signals over 250 km ultra-large effective area fiber,” IEEE Photon. Technol. Lett. 23(4), 239–241 (2011). [CrossRef]
  17. M. Nölle, J. Hilt, L. Molle, M. Seimetz, and R. Freund, “8×224 Gbit/s PDM 16QAM WDM transmission with real-time signal processing at the transmitter,” in 2010 36th European Conference and Exhibition on Optical Communication (ECOC) (2010), paper We.8.C.4.
  18. B. Olsson, J. Mårtensson, A. Kristiansson, and A. Alping, “RF-assisted optical dual-carrier 112 Gbit/s polarization-multiplexed 16-QAM transmitter,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2010), paper OMK5.
  19. R.-J. Essiambre, P. J. Winzer, and D. F. Grosz, “Impact of DCF properties on system design,” Opt. Fiber Commun. Rep. 5, 425–495(2007).
  20. P. Poggiolini, A. Carena, V. Curri, G. Bosco, and F. Forghieri, “Analytical modeling of nonlinear propagation in uncompensated optical transmission links,” IEEE Photon. Technol. Lett. 23(11), 742–744 (2011). [CrossRef]
  21. P. Poggiolini, G. Bosco, A. Carena, V. Curri, V. Miot, and F. Forghieri, “Performance dependence on channel baud-rate of PM-QPSK systems over uncompensated links,” IEEE Photon. Technol. Lett. 23(1), 15–17 (2011). [CrossRef]

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