The role of electronic modulation and signal processing in next generation fiber transport

In selecting techniques for commercial deployment at 40 Gb/s, it is important to focus on those technologies that help to achieve the following key goals: more cost-effective fiber plant operation, maintenance, and capacity upgrade via simplified multi-haul transport of 40 Gb/s and 10 Gb/s wavelengths over a common fiber plant; higher 40 Gb/s channel densities via reduced optical bandwidth; extended 40 Gb/s reach via enhanced tolerance to key fiber transmission impairments; lower system cost and more efficient utilization of facilities via simplified 40 Gb/s system implementation and more compact 40 Gb/s system footprint. We examine a variety of proposed new modulation formats and signal processing techniques in terms of their ability to support the above goals. The discussion is limited to systems utilizing direct detection, focusing primarily on modulation formats. A brief discussion is also included of the additional performance and economic benefits to be gained from electronic signal processing techniques such as electronic adaptive equalization, adaptive clock-and-data-recovery (CDR), and forward-error-correction (FEC). These complementary signal processing schemes are well established in lower-rate communication systems, such as voice channel modems, mobile radio, and digital subscriber lines. Coupled with advanced modulation techniques, they offer higher system performance, greater system flexibility and reconfigurability, more highly integrated electronic implementations, and ultimately lower system manufacturing, installation, and maintenance costs.