Ultrabroad-band Raman amplifiers pumped and gain-equalized by wavelength-division-multiplexed high-power laser diodes

This paper reviews recent progress in broad-band Raman amplifiers for wavelength-division-multiplexed (WDM) applications. After the fundamentals of Raman amplifiers are discussed in contrast to erbium-doped fiber amplifiers, a new technique called "WDM pumping" is introduced to obtain ultrabroad and flat gain in Raman amplifiers only using WDM diode pumps. The design issues of this technique are then developed to realize outstanding performances such as 100 nm of flat gain bandwidth, 0.1 dB flatness over 80 nm, and so forth.