Gaindistribution measurements along an ultralong erbiumdoped fiber amplifier using opticaltimedomain reflectometry

Optical gain changes as a function of distance along a long distributed erbium-doped fiber amplifier were measured, using optical-time-domain reflectometry. Two dispersion-shifted erbium-doped fibers with fiber lengths of 9-19 km and doping concentrations of 0.5 (0.5 x 10(-4) wt %) and 0.1 (0.1 x 10(-4) Wt %) parts in 10(6) have been tested, using 1.48-microm InGaAsP laser diode and 0.98-microm Ti:sapphire laser pump sources. It is shown how local gain and loss change with an increase in pump power.