Ultra long-haul transmission with multi-terabit capacity

As trans-Pacific terabit transmission systems have become commercially viable (Tsuritani et al, 2000; Bakhshi et al, 2001), intense research efforts are now being directed to multi-terabit system development. For cost-effective applications, the systems with only C-band optical repeaters should be preferred, although we must increase spectral efficiency significantly to accommodate the multi-terabit WDM channels within a few tens of nm of the C-band window. To enhance the spectral efficiency, the use of vestigial-sideband RZ (VSB-RZ) optical signals has been found promising. Another key issue for multi-terabit system applications is the use of higher bit rate signals, such as 40 Gbit/s, so that we can reduce the number of terminals for the same aggregate capacity. In this paper, we discuss these issues for ultra-long-haul system applications: practicality of VSB-RZ signal transmission and possibility of 40 Gbit/s-based WDM transmission.