Numerical analysis of (alpha) parameters and extinction ratios in InGaAsP-InP optical modulators

The (alpha) 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 (alpha) parameter for EA modulators and low driving voltages for MZ modulators. Bulk EA modulators are shown to inherently have relatively small (alpha) parameters; however, they also require a tradeoff between the extinction ratio and the insertion loss. The (alpha) parameters of symmetrical and (pi)-phase-shifted MZ modulators in the single- and dual-drive cases are also discussed.