ABSTRACT
The modulation of an optical signal is a key requirement of modern optical communications. Even when the transmitter is a laser diode, which can itself be directly modulated, there are advantages of using an unmodulated laser and an external modulator on the output. Optical modulators can be constructed using many different physical effects. Design of an electroabsorption modulator (EAM) requires accurate computation of its key characteristics. The optical absorption in EAMs is caused by several processes, among which are carrier transitions between conduction and valence band, free-carrier absorption, intraband transitions, photon–phonon interaction, etc. The Franz–Keldysh (FK) effect is the change in photon absorption spectrum induced by reverse bias applied to a bulk semiconductor structure. Modeling of the absorption spectrum as a function of voltage bias consists of several stages. Two most important effects contributing to the absorption is the carrier transitions between (a) energy levels created by QW confinement and (b) exciton binding energy levels.
