High optical coupling between hybrid III-V and SOI platform with grating-assisted co-directional couplers

The technology for heterogeneously integrating active III-V material structures on silicon photonic platforms has gained considerable advancement in recent years. Most of the prior work utilizes the silicon-on-insulator (SOI) platform with a thicker waveguide than the popular 220 nm thick silicon layer to achieve high coupling between the III-V waveguide and SOI waveguide. The thicker SOI waveguide results in closer effective refractive indices between the two heterogeneous waveguide structures to achieve better resonance conditions. Here, we demonstrate excellent light coupling from an active III-V structure to an SOI waveguide with a standard 220 nm Si waveguide by incorporating the grating-assisted co-directional coupler (GACC) method. The GACC grating structure can be formed on either side of the III-V and Si wafers. With the GACC scheme, a thicker adhesive for bonding the two different materials can be used. The simulation verifies that over 94 % energy coupling efficiency can be obtained by using a 100 nm thick DVSBCB as the bonding layer. High coupling performance can be maintained over a 40 nm wavelength range around 1550 nm. The high coupling efficiency can be achieved with good phase matching and mode matching between the super-modes of the hybrid structure.