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

Optical on-off modulators require low insertion loss, high contrast ra tio (CR), small drive power and large bandwidth or bit-rate. A systema tic approach to optimize the total performance of these modulators bas ed on the quantum-confined Stark effect is presented here. The approac h consists of minimizing the power/bandwidth ratio while satisfying a given CR and insertion loss. Our design consists of a large-core multi mode passive waveguide with a thin buried active layer. The passive wa veguide is designed to yield a high coupling efficiency to conventiona l single-mode fibers. The quantum well material structure is designed to maximize Delta alpha/Delta F-2, while maintaining a sufficiently la rge 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 s wing of the applied electric field. Our theoretical model shows that i ) wider quantum wells give larger Delta alpha/Delta F-2, and ii) the b andwidth/power ratio as high as 4 GHz/mW can be achieved simultaneousl y 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 contr ast ratio of 20 dB and a total insertion loss of 4.5 dB may also be ob tained.