JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 29, NO. 23, DECEMBER 1, 2011 3587 40 Gbps WDM Transmission Performance Comparison Between Legacy and Ultra Low Loss G.652 Fibers Erwan Pincemin, N. Boudrioua, Jaroslaw P. Turkiewicz, and T. Guillossou Abstract—G.652 standard single-mode fiber (SSMF) is today considered as the most efficient solution to transport 40 Gbps and 100 Gbps data traffic over ultra long-haul distances on terrestrial transport networks. In the early 2000s, there was a trend to replace legacy G.652 fibers, which were strongly impaired by polarization mode dispersion (PMD), by G.655 fibers. For economic reasons, incumbent operators decided to keep their legacy G.652 fiber infrastructure, while replacing gradually the most impaired fibers by low PMD G.652 fibers over the links transporting the highest amount of traffic. In this context, we performed in 2009 an experimental evaluation of the performance of a new ultra low loss (ULL) and low PMD G.652 fiber to carry 40 Gbps WDM systems over ultra long-haul distances by using various modulation formats (NRZ-OOK and NRZ-DPSK) and amplification schemes (hybrid Raman-EDFA and EDFA only). We demonstrated record transmission distance of 4400 km at 40 Gbps line rate when NRZ-DPSK was combined with hybrid Raman-EDFA amplification. We complete here this previous study with new results, coming in particular from an extensive experimental and numerical comparison of the transmission performance of this new ULL G.652 fiber with the legacy G.652 fiber, used in the field for 20 years. We demonstrate in particular that this new SMF-28 ® ULL optical fiber increases the maximum transmission reach by %, whatever the amplification scheme, when NRZ-DPSK is used. Index Terms—Legacy G.652 fiber, NRZ-DPSK, Raman amplifi- cation, ultra low loss G.652 fiber. I N THE EARLY 2000s, fiber manufacturers and system ven- dors presented the new ITU-T G.655 fiber standard (in- cluding LEAF ® [1], [2], Truewave ® [3], [4] and Teralight™ [5], [6] optical fibers) as the best solution to cope with the various propagation impairments affecting 40 Gbps long-haul WDM transmission. According to them, G.655 fibers presented the triple advantage of limiting the exacerbation of intra-channel non-linear effects, of reducing as much as possible the disper- sion compensation budget (owing to a lower chromatic disper- Manuscript received July 11, 2011; revised October 12, 2011; accepted Oc- tober 12, 2011. Date of publication October 19, 2011; date of current version November 30, 2011. E. Pincemin, N. Boudrioua, and T. Guillossou are with France Telecom, Or- ange Labs, 22307 Lannion, France (e-mail: erwan.pincemin@orange-ftgroup. com). J. P. Turkiewicz is with Telekomunikacja Polska, 02-691 Warsaw, Poland (e-mail: jaroslaw.turkiewicz@telekomunikacja.pl). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2011.2172774 sion than G.652 fiber), and of decreasing drastically polariza- tion mode dispersion (PMD) [7]–[9]. However, some incumbent operators resisted to these arguments and decided to keep their legacy G.652 fiber infrastructure, however severely affected by PMD. Behind this choice, there were primarily economic rea- sons but also the opinion that the evolution of transmission tech- niques had to solve the intrinsic limitations of the already in- stalled optical cables [10]–[14]. As, moreover, there was no fun- damental reason for G.652 fibers to present a worse PMD than G.655 fibers [15], [16], operators requested manufacturers to de- sign low PMD G.652 fiber and decided to progressively replace the most impaired legacy fibers by these low PMD G.652 fibers over the routes carrying the highest amount of traffic. In parallel, the 40 Gbps WDM transmission systems, which are or will be installed in a near future over the core transport networks of telecom carriers, have to reach similar maximum propagation distances as the already deployed ultra long-haul (ULH) 10 Gbps WDM systems (in order to be as cost-effi- cient as the 10 Gbps ones) and enable transparent networking at 40 Gbps. The targeted maximum transmission distances for ULH WDM systems, before electronic regeneration is needed, is typically of km. Although at 10 Gbps ULH reaches of 2000 km and beyond are commonly achieved on G.652 standard single-mode fiber, they present a challenge at 40 Gbps due to the requirement to get 6-dB higher optical signal-to-noise ratio (OSNR) at the receiver side and a four times lower PMD budget when compared to the 10 Gbps data rate. At a time when incum- bent carriers are beginning to replace their existing PMD-im- paired fiber infrastructure with low PMD G.652 fiber, it may be interesting for them to install over their long-distance trans- port networks both ultra low loss and low PMD G.652 fiber [17]–[19]. Hence, the deployment of future ULH 40 Gbps and 100 Gbps WDM transmission systems will be easier as a result of the lower PMD and the higher OSNR at the end of the link. In this paper, we present a systematic performance com- parison of 43 Gbps WDM transmission systems propagating over the new SMF-28 ® ULL optical fiber (ITU-T G.652 com- pliant) using various modulation formats (NRZ-OOK and NRZ-DPSK) and amplification schemes (hybrid Raman-EDFA and EDFA only). This study, which completes the work pub- lished in 2009 [17], reports in particular that the combination of hybrid Raman-EDFA amplification (with realistic backward gains) with NRZ-DPSK results in record transmission distance of 4400 km on G.652 fiber at 43 Gbps line rate, while the im- plementation of a simpler modulation format (NRZ-OOK) and amplification scheme (EDFA only) enables to reach 1600 km. 0733-8724/$26.00 © 2011 IEEE