Contribution of the band-filling effect to the effective refractive-index change in double-heterostructure GaAs/AlGaAs phase modulators

Abstract
In this work we have theoretically estimated the effective refractive‐index variation Δneff due to the removal of carriers in the depletion region of a double‐heterostructure (DH) n‐AlGaAs/n‐GaAs/p‐AlGaAs phase modulator when a reverse bias is applied to this structure. Δneff is calculated by a Kramers–Kronig analysis of the absorption spectrum, which changes around the absorption edge because of the band‐filling effect associated with the presence of carriers. We also calculated the phase shift Δφ due to Δneff, and we showed that this contribution due to the band‐filling effect can account for up to 28% of the total phase shift for a specific DH structure, showing in this way that the band‐filling effect can no longer be ignored in the analysis of phase modulators.