Relaxed Tolerance Low-Loss Adiabatic Si3N4 to Polymer Waveguide Coupler for Dense Interconnects

Despite significant advances in silicon photonics, optical packaging and interconnection of photonic integrated circuits constitutes a large portion of the associated manufacturing costs. Optical fibers are the dominant approach to optical interconnection. However, techniques that rely on fibers lack scalability, have low efficiency and show poor misalignment tolerance. Proposed alternative solutions using polymer waveguides have shown improved coupling efficiency, misalignment tolerance and scalability. Here we present the design, simulation and the experimental confirmation of an adiabatic silicon nitride taper to polymer waveguide coupler with only 0.52 dB of TE coupling loss at 1550-nm wavelength, excluding material loss. The coupler demonstrates $\pm 4~\mu \text{m}$ of lateral misalignment tolerance with a 1-dB penalty which, to the best of our knowledge, is the highest reported tolerance for silicon nitride to polymer waveguide coupling.