Spot size converter for improved coupling of standard single mode fibers to SOI waveguides

We present a spot size converter (SCC) for coupling standard single mode fibers with 10μm mode field diameter to 500nm × 220nm SOI waveguides. Thanks to the large mode supported at the SSC input, the device offers an alignment tolerance of ±2.2μm for 1dB excess loss, which is comparable to the alignment tolerance between two butt-coupled standard single mode fibers. An optimized design of the SSC tapers provides a low total coupling loss of 0.4dB at 1550nm for the TE mode at perfect alignment. The proposed spot size converter is fully compliant to industry standard microfabrication processes, and provides good robustness to typical fabrication tolerances.