Design analysis of upgrade strategies from single- to double- and triple-wavelength-band WDM transmission

To meet the demand for ever-increasing transmission capacity led by the increase in Internet traffic, up to 10 Tb/s transmission capacity experiments have been demonstrated using wavelength division multiplexing (WDM) and up to three transmission bands. Most of today's commercial WDM systems, however, are capable of 80 channels at 10 Gbit/s in the C-band and similar capacity in the L-band. 40 Gbit/s channel rate WDM systems are not yet commercially deployed. To achieve the aforementioned multi-terabit capacity systems for the future high spectral efficiency and the opening of additional transmission wavelength bands will be necessary. Besides the already used conventional C-band and the long-wavelength L-band the short wavelength S-band is the most promising candidate for a third transmission window. A key technology for accessing a new transmission band is the availability of optical amplifiers, which is fulfilled for the S-band by using either gain-shifted thulium doped fiber amplifiers or new erbium doped fiber amplifiers. In this paper we will provide an overview of amplifier types and their possible usage to upgrade to multi-band transmission as well as we will discuss general design options for upgrading transmission bands. In particular, we will show numerical results for Raman based C- and L-band amplification with multiple Raman pumps and different pumping schemes and an experiment for opening up the S-band by a fiber amplifier approach.