Due to the large difference in mode size and effective-index mismatch between the optical fiber and the waveguides on the photonic integrated circuits, it is a big challenge to efficiently couple light into thin semiconductor waveguides. In this paper, a taper plasmonic coupler is presented to couple fiber light into an Si waveguide. The taper plasmonic coupler structure is optimized, and the alignment tolerance of the gap, the lateral offset and the vertical offset between coupler and Si waveguide are studied. Numerical simulation shows that the coupler changes the single mode fiber light to multimode light at its input port section, while at its output port section, the coupler turns the multimode light back to a single mode light, and finally couples this light to Si waveguide. The maximum couple efficiency is 86.8% in [Formula: see text] effective coupler length.
