The mode size converter is constructed with two-dimensional tapered Si waveguides and
overlaid high-index polymer waveguides. We calculated the proposed mode size converter
characteristics, and fabricated 1.09 mm length Si wire waveguides with the converters. The
measured loss of the mode size converter was 0.8 dB per conversion, and the total insertion
loss through the sample with an Si wire waveguide was 3.5 dB.