by Christian Rasmussen, Tina Fjelde, Jon Bennike, Fenghai Liu, Supriyo Dey, Benny Mikkelsen, Pavel Mamyshev, Peter Serbe, Paul van der Wagt, Youichi Akasaka, David Harris,
Denis Gapontsev, Vladlen Ivshin, Peter Reeves-Hall

Index Terms-40 Gbit/s, Differential phase shift keying, Dispersion mapping, Forward error correction, Optical fiber dispersion, Optical transmitters, Optical receivers, Precoding, Raman amplification, Ultra long distance transmission

INTRODUCTION
The many recent impressive DWDM 40G transmission demonstrations over distances up to about 9000 km [1-12] clearly show the rapidly improving performance of 40G transmission equipment and techniques, and in the present paper we present error-free transmission of 40x40 Gbit/s over a new record distance of 10,000 km with 100 km spans [13].

The trans-Pacific transmission distance of 10,000 km was achieved by combining for the first time, to our knowledge, CSRZ-DPSK, enhanced FEC (EFEC), distributed Raman amplification, and dispersion-managed fiber spans. An additional key factor in achieving this distance is the implementation of a transmitter/receiver pair with a back-to-back OSNR sensitivity of 11.3 dB at a BER of 10^-12. This is only 1 dB from the theoretical limit and we believe it is the best reported result at 40G. It should also be emphasized that DPSK precoding is done at 40G using 50G logic (an AND gate and a T-flip-flop) and that EFEC decoding is fully implemented.

Authors:
Christian Rasmussen, Tina Fjelde, Jon Bennike, Fenghai Liu, Supriyo Dey, Benny Mikkelsen, and Pavel Mamyshev are with Mintera Corporation, USA

Peter Serbe is with Huber+Suhner AG, CH-8330 Pfaeffikon ZH, Switzerland

Paul van der Wagt is with Inphi Corporation, Westlake Village, CA 91361, USA

Youichi Akasaka and David Harris are with Sprint, Advanced Technology Labs, Burlingame, CA 94010, USA

Denis Gapontsev, Vladlen Ivshin, and Peter Reeves-Hall are with IPG Photonics Corporation, Oxford, MA 01540, USA