Modelling and simulation of electroabsorption modulators

A synopsis of different methods of modelling electroabsorption modulators based on multiple quantum wells (MQW) is given. It contains two algorithms which are based on the density matrix formalism. A first estimation of the spectral absorption of the quantum wells is gained by expanding the excitonic states in terms of sub-band states. Another efficient and more appropriate model is the direct solution of the density matrix using a perfectly matched layer (PML) absorber to limit the calculation domain. A drift-diffusion model self-consistently corrected by the Bohm potential describes the quantum transport properties. The exciton equation and the transport model are iteratively coupled and, thus, account for nonlinear, carrier-dependent effects. The model includes bound and unbound states, avoids the Kramers-Kronig. relation and considers important effects contributing to electroabsorption, such as the Franz-Keldysh effect, the Wannier-Stark effect and the quantum-confined Stark effect. The time-dependent problem is solved by implicit, rather than by explicit algorithms as the latter demand very restrictive stability conditions