Novel adiabatic coupler for III-V nano-ridge laser grown on a Si photonics platform

While III-V lasers epitaxially grown on silicon have been demonstrated, an efficient approach for coupling them with a silicon photonics platform is still missing. In this paper, we present a novel design of an adiabatic coupler for interfacing nanometer-scale III-V lasers grown on SOI with other silicon photonics components. The starting point is a directional coupler, which achieves 100% coupling efficiency from the III-V lasing mode to the Si waveguide TE-like ground mode. To improve the robustness and manufacturability of the coupler, a linear-tapered adiabatic coupler is designed, which is less sensitive to variations and still reaches a coupling efficiency of around 98%. Nevertheless, it has a relatively large footprint and exhibits some undesired residual coupling to TM-like modes. To improve this, a more advanced adiabatic coupler whose geometry is varied along its propagation length is designed and manages to reach ∼100% coupling and decoupling within a length of 200 μm. The proposed couplers are designed for the particular case of III-V nano-ridge lasers monolithically grown using aspect-ratio-trapping (ART) together with nano-ridge engineering (NRE) but are believed to be compatible with other epitaxial III-V/Si integration platforms recently proposed. In this way, the presented coupler is expected to pave the way to integrating III-V lasers monolithically grown on SOI wafers with other photonics components, one step closer towards a fully functional silicon photonics platform.