Application of adiabaticity map: highly efficient coupling from optical fibers to silicon waveguides by adiabatic mode evolution

Efficient coupling of light from an optical fiber to silicon waveguides is a challenging task in integrated photonics. Couplers based on adiabatic mode evolution have the advantages of high bandwidth and low loss but are often accompanied by longer device lengths. In this paper, we introduce the concept of adiabaticity map and optimize the coupling between an optical fiber and Si waveguides by selecting routes on the map that minimize unwanted mode coupling. The map clearly indicates areas in mode evolution where supermode coupling is large and identifies optimal routes for efficient mode evolution. Optimized interaction length and widths are obtained from the adiabaticity map. We obtain highly efficient coupling (96%) with large bandwidth (1-dB bandwidth 280 nm) and misalignment tolerance (⪆90 nm lateral misalignment range for 1-dB excess losses) for the TE polarization.