Waveguide-pair design cooptimization and tolerance study for CMOS-compatible hybrid III–V/Si quantum dot DBR lasers

The development of compact, energy-efficient integrated lasers operating at 1.3 µm remains a central goal in silicon photonics, driven by the needs of data communication and optical interconnect applications. In this study, we investigate the lateral co-optimization of the coupled III–V/Si waveguide pair in hybrid quantum-dot (QD) distributed Bragg reflector (DBR) lasers. The vertical platform is fixed to a 400-nm-thick silicon waveguide and an optimized five-QD III–V stack with Al_0.4Ga_0.6As claddings, identified in our companion epitaxial study as the smallest silicon thickness that recovers robust supermode transfer without tapering the III–V ridge for this epitaxial structure. We then sweep the silicon-waveguide width and track the confinement factors and mode profiles of the resulting hybrid supermodes. Narrow widths keep the fundamental mode predominantly in the III–V active region for the pumped gain window, while wider widths transfer it into the silicon waveguide for the passive DBR and output sections. The confinement crossover occurs near 1.3 µm width, providing clearly separated design windows on either side for active and passive operation. The evolution is smooth over several hundred nanometers, which is useful for lithographic margin when the operating points are chosen away from the crossover. These results define a practical width map and clarify the residual trade-off between modal discrimination and silicon waveguide width in hybrid III–V/Si QD DBR lasers.