A universal optical heterostructure for photonic integrated circuits: a case study in the AlGaAs material system

An approach for the realization of a single heterostructure for multiple optical device applications in a photonic integrated circuit environment is addressed from the standpoint of building into the heterostructure separate device features. In particular, a low compositionally graded depressed cladding laser structure is shown to have a large mode, compared to a structure optimized for maximum confinement factor, and a radiation loss an order of magnitude lower than for a structure without the inner cladding, features which are important for fiber coupling and for compact bends. By incorporating a narrow gap section into the barrier layer, a bulk electroabsorption modulator can be integrated into the same structure that contains quantum wells for optical amplifiers. Data are presented on the device properties of a single heterostructure when used as large optical cavity lasers, s-bends, and bulk electroabsorption modulators. The only laser parameter affected by the incorporation of the modulator is the transparency current density which is increased 25% over standard structures. The performance of rib delineated s-bends is exceeded only by native oxide defined small optical cavity laser structures. The electroabsorption modulator, which was activated in a disordered section under reverse bias, had a modulation depth approximately 1/3 that predicted by model studies which was attributed to the depletion electric field profile. Methods for improving the modulation depth while lowering the transparency current density are outlined.