Limiting effects in densely doped erbium amplifiers

Optical fibers and planar waveguides doped with erbium ions offer numerous attractive features for use as amplifiers or lasers in the important communication window around 1.5µm. An important aspect for the realization of practical amplifiers is the achievement of a high gain at a reasonable pump power, i.e., the gain efficiency should be high. In a standard erbium-doped fiber amplifier (EDFA) of typically a few meters length and with a moderate erbium concentration (<1000 ppm), gains larger than 30 dB and gain efficiencies of a few dB/mW can be readily achieved.