The commercial availability of erbium-doped fiber amplifiers has fueled the explosive growth of dense wavelength division multiplexing optical networks. These multiplexed optical systems in turn place great demands on amplifier performance. This market pull presents both challenges and opportunities for amplifier manufacturers and test instrument vendors. Erbium-doped fiber amplifiers must be accurately characterized at the production line and before the field installation. Production testing systems for erbium-doped fiber amplifiers consist primarily of laser sources, measurement instruments (e.g., optical spectrum analyzers) and optical branching components. The International Telecommunications Union wavelength grids define the laser sources. The present ITU-T standard uses a Krypton line at 193.10 THz as reference and an even channel spacing of 100 THz. This correlates to approximately 1552.52 nm in vacuum and a channel spacing of about 0.8 nm. Selecting the right laser sources and ensuring measurement accuracy are two critical issues while designing an amplifier test system.