Enhanced modulation bandwidth for strain-compensatedInGaAlAs-InGaAsP MQW lasers

摘要

Strain-compensated (SC) multiple-quantum-well (MQW) lasers werendesigned using tensile-strained InGaAlAs barrier layers in order tonenhance the modulation bandwidth of MQW lasers at 1.55 Μm. The designnscheme simultaneously ensures the pseudomorphic growth of a large stacknof highly strained wells, a uniform hole injection into large number ofnwells, a large conduction band discontinuity to suppress the carriernoverflow effect, and a large differential gain by suppressing the bandnmixing effect. The SC-MQW structures were processed into a mushroomnstripe laser structure to obtain a low parasitic capacitance. The numbernof wells and the cavity length were optimized to maximize the modulationnbandwidth. Both the relaxation oscillation and RC cutoff frequenciesnincreased with reducing the cavity length, and a maximum 3-dB modulationnbandwidth of 30 GHz was obtained at a short cavity length of 120 Μmnfor 20-well SC-MQW lasers. Moreover, a high internal quantum efficiencynand large differential gain were obtained for the SC-MQW lasers withnwell numbers of up to 20 as a result of the reduced carrier transportnand overflow effects. The differential gain, gain compression factor,nand K factor were evaluated experimentally from the modulationncharacteristics and compared to the theoretical calculation based on thenspectral hole burning theory. The observed experimental results werenwell explained by the model using the identical intraband relaxationntimes typically used for 1.55-Μm bulk lasers