Cascade of two opposite tapers for butt-coupling between fibers and silicon photonic wires with large misalignment tolerance and low polarization dependency

A new coupler design consisting of a three-dimensional SU-8 taper and a silicon inverted nanotaper is presented. The fiber misalignment tolerance is ±3 μm and the coupler loss is 2.8 dB(TE) and 4.1 dB(TM).