Highly Efficient Broadband Adiabatic Mode Transformation Between Single-Mode Fibers and Silicon Waveguides

High-efficiency optical energy transfer between dissimilar waveguides is critical for establishing seamless interconnects between heterogeneous photonic systems. Broadband optical coupling between a silica single-mode optical fiber and a silicon integrated waveguide at near-infrared wavelengths has been especially challenging because of significant differences in their refractive indices and waveguide dimensions. We demonstrate highly efficient broadband optical coupling based on adiabatic mode transformation between axially overlapped tapered waveguides, with a specific focus on TE polarization. Sub-decibel optical coupling losses across the entire telecommunication O- and C-bands with large mechanical misalignment tolerances may significantly lower the connectivity barrier between low-loss optical fibers and densely integrated photonic devices for various emerging applications in both classical and quantum photonics.