Ultracompact adiabatic tapered coupler for the Si/III-V heterogeneous integration

An ultracompact bi-sectional tapered coupler, suitable for adiabatic mode transformation between a common single mode SOI strip waveguide and a Si/III-V hybrid waveguide, is proposed for Si/III-V heterogeneous integration. Since the bi-sectional tapered coupler mimics a semi-3D taper and avoids exciting unwanted high-order modes in the thick p-InP cladding layer (which is removed in the first tapered section), the length of the adiabatic mode coupler can be dramatically shortened. In the proposed structure, the length of the bi-sectional tapered coupler can be as short as 9.5 μm with a large fundamental mode-coupling ratio (over 95%) in a bandwidth of ∼ 100 nm, and provides ±100nm tolerance to misalignment even when the bonding layer is as thick as 50 nm.