A simplified laser-to-chip edge coupling scheme using 3D SU-8 taper

Abstract

In this work, we design and simulate a three-dimensional (3D) SU-8 tapered edge coupler for effectively guiding light from an edge-emitting semiconductor laser diode directly to a silicon waveguide to realize a hybrid on-chip silicon light source. A series of coupling efficiencies for the commonly used top silicon thicknesses of the silicon-on-insulator wafers from 220 to 3000 nm are obtained, showing that this polymer taper can largely improve the coupling efficiency when the silicon waveguide thickness is moderate, for instance, from 41% (with no taper) to 67% for the 700 nm- thick silicon waveguide under 1 μm gap offset and relax the lateral misalignment tolerance to above one micron by suppressing the butt refractive index contrast and the mode mismatch between the laser diode and the silicon waveguide. Wave transformation inside the tapered coupler and the input silicon waveguide has also been revealed by 3D finite-difference time-domain simulations. This 3D tapered coupler is cost effective and easily fabricated which can have wide practical applications in massive production of various silicon photonic chips based on the present complementary metal-oxide-semiconductor foundry.