ENHANCED MODULATION BANDWIDTH FOR STRAIN-COMPENSATED INGAALAS-INGAASPMQW LASERS

Strain-compensated (SC) multiple-quantum-well (MQW) lasers mere design ed using tensile-strained InGaAlAs barrier layers in order to enhance the modulation bandwidth of MQW lasers at 1.55 mu m. The design scheme simultaneously ensures the pseudomorphic growth of a large stack of h ighly strained wells, a uniform hole injection into large number of we lls, a large conduction hand discontinuity to suppress the carrier ove rflow effect, and a large differential gain by suppressing the band mi xing effect. The SC-MQW structures were processed into a mushroom stri pe laser structure to obtain a low parasitic capacitance, The number o f wells and the cavity length were optimized to maximize the modulatio n bandwidth. Both the relaxation oscillation and RC cutoff frequencies increased with reducing the cavity length, and a maximum 3-dB modulat ion bandwidth of 30 GHz was obtained at a short cavity length of 120 m u m for 20-well SC-MQW lasers. Moreover, a high internal quantum effic iency and large differential gain were obtained for the SC-MQW lasers with well numbers of up to 20 as a result of the reduced carrier trans port and overflow effects, The differential gain, gain compression fac tor, and It factor were evaluated experimentally from the modulation c haracteristics and compared to the theoretical calculation based on th e spectral hole burning theory, The observed experimental results were well explained by the model using the identical intraband relaxation times typically used for 1,55-mu m bulk lasers.