A new adiabatic coupling design between the III-V gain section and SOI waveguide for the heterogeneously integrated SOA with high coupling efficiency and large process tolerance

Heterogenously-integrated semiconductor optical amplifiers (SOA) on the silicon photonics platform have demonstrated advantages such as on-line optical amplification、small figure size and high nonlinearity. While, maintaining high coupling efficiency and large fabrication tolerance at the same time for the coupling between the IIIV optical amplification section and silicon on insulator (SOI) waveguide is still a challenge. Although the edge coupling and abrupt coupling have less alignment accuracy requirements, the total coupling loss is still high due to the mode mismatching. The adiabatic taper structure demonstrates a low coupling loss while the starting width of the active taper is typically down to 100 nm (or even smaller). Especially, it will lead to an unstable mode distribution within the quantum well gain region when it is extended until 1 micron. In this paper, we propose a novel coupling structure involving a slanted active taper structure on top of a smoothly-bending Si waveguide. FDTD/EME simulation results demonstrate that the overall coupling efficiency can be optimized to a level of more than 98% even that the active taper width is up to 1 micron, and the confinement factor in the quantum well can still be stable around 3.8% overall the whole coupling structure. This structure can be beneficial to improve the saturation power of heterogeneous integrated SOA.