LONGITUDINAL SPATIAL HOLE-BURNING AND ASSOCIATED NONLINEAR GAIN IN GAIN-CLAMPED SEMICONDUCTOR OPTICAL AMPLIFIERS

The longitudinal spatial hole burning (LSHB) in gain-clamped semicondu ctor optical amplifiers (GCSOA's) is investigated by means of a numeri cal model, which is based on position-dependent rate equations for the carrier density and the propagation equations for the optical power, The simulation results show that the carrier densities are nonuniforml y distributed within the active layer of GCSOA's, The nonuniformity ca n be large, especially for high currents and optical signal powers nea r the saturation. It is found that the LSHB induces a gain nonlinearit y, which causes interchannel cross talk when GCSOA's are used in wavel ength division multiplexing (WDM) applications. In order to reduce thi s gain nonlinearity, two methods are analyzed: the use of low resistiv ity devices and the use of unbalanced Bragg mirror reflectivities.