Antoine Tan & Erwan Pincemin France Telecom, R&D Division

1. externeGroupe Performance Comparisonof Duobinary and DQPSK Modulation Formatsfor Mixed 10/40-Gb/s WDM Transmissionon SMF and LEAFTM Fibers Antoine Tan & Erwan Pincemin France Telecom, R&D Division e-Photon-ONe+, Workshop VD-T, Brest, July 16th, 2007

2. Introduction • Duobinary & DQPSK formats: the best candidates for the deployment of 40 Gb/s technology on existing 10 Gb/s WDM long-haul transmission systems. • The Duobinary format has attracting characteristics: • Compact spectrum enabling 50-GHz channel spacing transmission. • High tolerance to residual chromatic dispersion (3 times greater than NRZ). • But • Poor tolerance to accumulation of ASE noise and PMD (worse than NRZ). • The DQPSK format represents a more powerful solution than Duobinary for transmission applications with higher reaches: • Compact spectrum compatible with 50-GHz channel spacing. • Good resilience to accumulation of ASE noise, PMD, CD, nonlinear effects. • In mixed 10/40-Gb/s 50-GHz WDM transmission, the main limitation comes from cross nonlinearities between 10 Gb/s NRZ channels and neighboured 40 Gb/s Duobinary or DQPSK signals. In this context, what is the behavior of the most worldwide deployed fiber (SSMF & LEAFTM) ?

3. PSBT Transmitter " Electrical " PSBT pre pre pre - - - PPG PG PG coder coder coder 5 5 order order Bessel LPF@11.2 GHz Bessel LPF@11.2 GHz th th " Optical" PSBT Receiver BERT PG Square Flat-Top BPF BPF 50 GHz 5th Bessel LPF@ 28 GHz pre decoder Duobinary Tx/Rx configuration • Industrial implementation of Duobinary format is also called PSBT. D. Penninckx et al, Phot. Techn. Lett., 9 (1997), 259-261 NRZ Duobinary NRZ Duobinary

4. DQPSK Transmitter " Electrical " PSBT pre pre - - PPG PPG PG PG PG PG p/2 precoder coder coder 5th Bessel LPF@ 14 GHz + - pre " Optical" DQPSK Receiver decoder + - 5th Bessel LPF@ 14 GHz BERT BERT PG PG NRZ Square Flat-Top DQPSK BPF BPF 30 GHz Duobinary DQPSK Tx/Rx configuration t=50 ps t=50 ps Duobinary NRZ DQPSK

5. DCF DCF DCF DCF DCF DCF DCF DCF DCF DCF Rx Rx SSMF LEAF LEAF SSMF LEAF SSMF LEAF SSMF LEAF SSMF Tunable Postchirp Tunable Postchirp SSMF Line " Electrical " Prechirp=- 210 ps/nm Prechirp=- 850 ps/nm DCF DCF DCF DCF DCF DCF DCF DCF DCF DCF PSBT Tx Tx SSMF LEAF LEAF SSMF LEAF SSMF LEAF SSMF LEAF SSMF " Optical" LEAF TM Line Transmission line configurationParameters for numerical simulations • 10 spans of 100-km long SMF fiber (17 ps/nm/km, 0.2 dB/km) + 16.66-km long DCF fiber (-100 ps/nm/km, 0.6 dB/km). • 10 spans of 100-km long LEAFTM fiber (4.2 ps/nm/km, 0.2 dB/km) + 4.116-km long DCF fiber (-100 ps/nm/km, 0.6 dB/km). • 98% compensation ratio. • Noise figure of each EDFA: 5 dB. • A symmetric dispersion map in order to limit impact of intra-channel nonlinearities. • - 2 dBm injected in each DCF module to minimize nonlinearities in DCF. • Post-chirp was optimized after each transmission configuration change. • 5 WDM channels ranged on a 50-GHz ITU grid: 1 Duobinary or 1 DQPSK 40 Gb/s channel surrounded by 4 NRZ 10 Gb/s channels. • VPI Transmission Maker with 2048 bits long PRBS sequences.

6. Duobinary DQPSK NRZ NRZ DQPSK Duobinary NRZ Duobinary DQPSK Back-to-back performances • Back-to-back OSNR sensitivity: 3 dB better than NRZ, 5 dB better than Duobinary @ 10-9. • Residual CD: 350 ps/nm for Duobinary, 250 ps/nm for DQPSK, and only 70 ps/nm for NRZ. • DGD robustness: > 16 ps for DQPSK, 8 ps for NRZ, and only 6 ps for Duobinary. • DQPSK represents a better trade-off for upgrading @ 40 Gb/s 10 Gb/s ULH transmission systems.

7. Transmission performances on SSMF & LEAFTM with mixed 10/40 Gb/s channels LEAF SSMF SSMF SSMF LEAF LEAF LEAF • PSBT works better on LEAF than on SSMF: 3-dB more span input power for LEAF. • At the opposite, DQPSK works better on SSMF than on LEAF: 3-dB more span input power for SSMF. • DQPSK is significantly more efficient than PSBT on SSMF (the fiber of incumbent carriers). • XPM generated by transmission on LEAF is dramatically more detrimental for DQPSK than for PSBT (by generating a large amount of nonlinear phase noise).

8. Transmission performances on SSMF & LEAFTM with only 40 Gb/s channels SSMF LEAF LEAF SSMF • When WDM channels are added, no extra BER penalty seems to be generated. Intra-channel nonlinear effects largely determine the transmission performance of 40G DQPSK. • 40G DQPSK WDM transmission is better (slightly) on SSMF than on LEAF. • 40G WDM transmission with only DQPSK channels operates easily on both SSMF & LEAF when compared with mixed 10/40G NRZ/DQPSK channels. • DQPSK • As expected, with only 40G PSBT channel propagation, XPM impacts dramatically more transmission on LEAF than on SSMF. • PSBT

9. Conclusions • We have led a performance comparison study of Duobinary and DQPSK formats for mixed 10/40 Gb/s 50-GHz WDM transmissions. • DQPSK represents the best trade-off in terms of back-to-back performances: • DQPSK has the best OSNR sensitivity, and the best resilience to DGD. • In terms of mixed 10/40 Gb/s 50-GHz spaced WDM transmission: • DQPSK modulation format is very efficient on SSMF and show a poor resilience to XPM on LEAF. • At the opposite, PSBT works very well on LEAF and is largely less efficient on SSMF. • In terms of 40 Gb/s only 50-GHz spaced WDM transmission: • No significant OSNR penalty is observed between 40G single-channel and 40G only 50-GHz WDM DQPSK transmissions on both SSMF and LEAF, even if SSMF works slightly better than LEAF. • 40G only 50-GHz spaced WDM PSBT transmission works significantly worse than DQPSK transmission on both SSMF and LEAF.

10. Thank you for your attention Questions ?