Numerical analysis of α parameters and extinction ratios in InGaAsP-InP optical modulators

The α parameters and extinction ratios of InGaAsP-InP electroabsorption (EA) modulators and Mach-Zehnder (MZ) modulators are theoretically investigated. The bound states of excitons in quantum wells (QWs) under electric field are calculated through the finite-difference method, and quasi-bound states are obtained by the transfer-matrix method. Reducing the heights of the potential barriers of the QWs is prerequisite to achieving small values of the α parameter for EA modulators and low driving voltages for MZ modulators. Bulk EA modulators are shown to inherently have relatively small α parameters; however, they also require a tradeoff between the extinction ratio and the insertion loss. The α parameters of symmetrical and π-phase-shifted MZ modulators in the single- and dual-drive cases are also discussed.