40-Gb/s upgradability of 10-GB/S systems

This paper presents the next logical step in network economy, the 40 Gb/s rate per WDM channel. The 40 Gb/s technology is mature enough that the transition from 10 Gb/s to 40 Gb/s, contrary to the previous transition from 2.5 Gb/s to 10 Gb/s, is evolutional and, therefore, much less painful for the carriers. Specifically, during this evolutional transition, already installed 10 Gb/s WDM systems can be in-service upgraded to 40 Gb/s by adding 40 Gb/s line cards (transmitters and receivers) instead of 10 Gb/s line cards. This upgrade process is called 40 Gb/s overlay on existing 10 Gb/s transmission infrastructure. Such upgradeability required solutions, which are: dispersion tolerance of 40 Gb/s receivers; 40 Gb/s transmission should work on all types of transmission fiber; 10 Gb/s and 40 Gb/s dispersion map compatibility; granularity of DCF modules; filtering by optical Mux/DeMux; and PMD.