Single-channel to multi-channel upgrade of 10-Gb/s transmission systems by Raman amplification

We have demonstrated an upgrade technique, which allows one to upgrade a single-channel 10 Gb/s transmission system to a four-channel WDM system with a total capacity of 40 Gb/s without changes to the transmission fiber. Raman gain from 1-W of diode pump power increases the power budget by 7.4 dB corresponding to sensitivities of -45.1 dBm or better for all channels. The pump wavelength of 1453 nm was selected for optimum performance in the 1550 nm to 1560 nm range. The transmitter consists of one DFB laser (in the case of single-channel measurements) or four DFB lasers (for the WDM measurements), which are then combined in a fiber directional coupler.