Analysis of the Optical Coupling Between GaSb Diode Lasers and Passive Waveguides: A Step Toward Monolithic Integration on Si Platforms

We simulate the optical coupling between $2.3\ {\boldsymbol{\mu m}}$ GaSb-based diode lasers (DLs) epitaxially grown on on-axis silicon (001) and passive waveguides in the butt-coupling geometry. 3D FDTD simulations reveal how the optical coupling is affected by the air gap between the laser cavity and the waveguide that arises from the laser etched-facet definition. We also model alternative approaches consisting in filling the gap with higher-refractive index materials transparent in the mid-infrared window. Finally, because of their fabrication flexibility, we propose to implement polymeric waveguides in order to achieve improved coupling performances.