I. Introduction
Differential phase-shift keying (DPSK) has become the format of choice for long-haul optical fiber transmission [1], [2]. Its sensitivity improvement and larger tolerance to fiber nonlinearities make it especially attractive for 40-Gb/s long-haul transmission. In a 40-Gb/s transmission system using DPSK, dispersion management is crucial for reducing nonlinear penalties. A periodic inline dispersion map is widely used currently [3]–[5]. Inline dispersion compensation adds complexity to transmission path design and maintenance, which can be simplified by using a single fiber type over the entire transmission distance. A lumped dispersion compensation scheme was introduced early in 40-Gb/s RZ on–off keying (OOK) transmission experiment [6]. Recently a transoceanic 10-Gb/s RZ-DPSK wavelength-division-multiplexing (WDM) transmission over nonzero dispersion-shifted fiber without use of periodic dispersion management was reported [7], showing similar performance to conventional maps. To the best of our knowledge, there have been no reports on lumped dispersion compensation for 40-Gb/s DPSK transmission.