2.1 Introduction

For those steeped in the lore of ordinary solitons, dispersion management, with its strong periodic variation in pulse properties, is strongly counterintuitive. Nevertheless, in 1995, in a seminal paper, Suzuki et al. [ ^[14]] reported experimental demonstration of essentially error-free 20-Gbit/s soliton transmission over 9000 km through strong reduction of the normally limiting Gordon-Haus jitter. The trick was to use a periodic dispersion "map" that allowed the soliton pulse energy to remain fixed in the face of greatly reduced D. A rash of papers soon followed, pursuing the enhanced energy [ ^{[15] [16] [17] [18]}] and general pulse dynamics [ ^{[19] [20] [21] [22] [23] [24]}] of these "dispersion-managed solitons." Thus this early, almost exclusively numerical work was largely focused on the behavior of isolated pulses, as were some following real-world experiments [ ^{[25] [26] [27] [28] [29] [30]}].

Papers on "dense WDM" (wavelength division multiplexing involving many, closely spaced channels) with dispersion-managed solitons tended to come somewhat later [ ^{[31] [32] [33] [34] [35]}]. Nevertheless, as we shall soon see, dispersion management is of tremendous importance to dense WDM. Dispersion-managed solitons in particular offer unique advantages for the formation of ultra-long-haul, dense WDM, all-optical networks. Before we can even begin to discuss these advantages, however, we must first have the quick overview of dispersion management and dispersion-managed solitons provided by the following section.