Short-length erbium-doped waveguide amplifiers and high-erbium-concentration effects

Erbium-doped fibers are now well established as efficient optical amplifiers for lightwave telecommunications systems at 1.5 μm. The characteristic length of such fibers is of the order of 5 to 50 m. A recent and growing effort is oriented towards the goal of fabricating high-gain erbium-doped waveguide amplifiers with lengths of the order of a few centimeters.1 As a result of the short length, the concentration of erbium required for appreciable gain is several orders of magnitude higher in the short waveguide amplifiers than in the fiber amplifiers, which gives rise to a number of potentially deleterious effects on the amplifier performance. Nevertheless, high-gain waveguide amplifiers have recently been demonstrated, with gains as high as 3.3 dB/cm in a 4.5-cm-long device.2