THEORETICAL DESIGN OPTIMIZATION OF MULTIPLE-QUANTUM-WELL ELECTROABSORPTION WAVE-GUIDE MODULATORS

Optical on-off modulators require low insertion loss, high contrast ratio (CR), small drive power and large bandwidth or bit-rate. A systematic approach to optimize the total performance of these modulators based on the quantum-confined Stark effect is presented here. The approach consists of minimizing the power/bandwidth ratio while satisfying a given CR and insertion loss. Our design consists of a large-core multimode passive waveguide with a thin buried active layer. The passive waveguide is designed to yield a high coupling efficiency to conventional single-mode fibers. The quantum well material structure is designed to maximize Delta alpha/Delta F-2, while maintaining a sufficiently large Delta alpha/alpha(0), where Delta alpha is the absorption change, alpha(0) is the residual absorption at zero bias, and Delta F is the swing of the applied electric field. Our theoretical model shows that i) wider quantum wells give larger Delta alpha/Delta F-2, and ii) the bandwidth/power ratio as high as 4 GHz/mW can be achieved simultaneously with small insertion loss. For example, with a drive voltage of 3 V, an RC limited bandwidth as high as 60 GHz is predicted, while a contrast ratio of 20 dB and a total insertion loss of 4.5 dB may also be obtained.