Christian Rasmussen (1), Supriyo Dey (1), Fenghai Liu (1),
Jon Bennike (1), Benny Mikkelsen (1), Pavel Mamyshev (1),
Kent Springer (1),
Denis Gapontsev (2), Vladlen Ivshin (2)

1: Mintera Corporation
2: IPG Photonics Corporation, 50 Old Webster Road, Oxford, MA 01540, USA

Introduction
The price per bit per km is a decisive figure of merit for optical transport systems. This means that long unregenerated transmission distances are very important. The possible transmission distance at 40G continues to increase thanks to advances in forward error correction (FEC), modulation formats, fiber types and amplification schemes. Recent impressive WDM transmission demonstrations include [1-8].

In this paper we report record 40G transmission over 5200 km UltraWave fiber with 100 km spans using turn-key electronic time division multiplexing (ETDM) transmitter and receiver. We used the robust and practical CS-RZ modulation format, all-Raman amplification and enhanced FEC (EFEC). FEC with higher coding gain is a key to increasing transmission distances without adding complexity to the transmitter and receiver. However, especially for 40G ETDM systems, it is important to limit the overhead to avoid penalties due to limited component bandwidth. The EFEC used in our demonstration has 8.7 dB coding gain with 7% overhead. Our demonstration shows that even for terrestrial span lengths, the achievable WDM transmission distance at 40G is approaching transatlantic distances.