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Optical modulation and bistability using bulk Franz-Keldysh effect in GaAlAs-GaAsAg asymmetric Fabry-Perot device structures

In this paper we report novel high contrast, high reflectivity n+-AlGaAs/GaAsAl/Ag asymmetric Fabry-Perot (ASFP) optical modulators and self-electro-optic devices (SEED) using the Franz-Keldysh (FK) electroabsorption in bulk GaAlAs layer. These modulators exhibit `normally off' and `normally on' optical modulation at and below the band edge with contrast ratios in the range of 25:1 to 200:1 and reflectivities of about 30% to 50%. We show that our experimental data is consistent with a model of electroabsorption that includes unbound excitons. The FK-SEED, exhibiting contrast rations of approximately 90:1 and reflectivities of 27% at 11 V, operates based on the combined effects of negative electroabsorption and the `normally off' properties of the device. In addition to these devices operating in the 10 nm vicinity of the GaAs band gap (872 nm), we also report a high contrast modulator with Ga0.975Al0.025As FK layer operating at the standard 850 nm wavelength. These devices demonstrate the feasibility of using the bulk Franz-Keldysh effect as an alternative to quantum confined stark effects (QCSE) for efficient optical switching and modulation for many applications.