Spotsize converter with improved design for InP-based deep-ridge waveguide structure

An efficient spotsize converter (SSC) is necessary for directly coupling an InP-based deep-ridge waveguide structure to a fiber. We have already proposed an SSC that uses a laterally buried taper, selectively grown over a thick cladding layer and an optimized deep-ridge-buried waveguide junction. The experimentally obtained converter loss was less than 2 dB, which is still large. Further optimization is possible by introducing a short taper waveguide for the deep-ridge-buried waveguide junctions and improving the taper shape by using a two-step linear taper with a short narrow waveguide. A simulation result shows that we can achieve a converter loss of less than 1 dB with a converter length of only 200 μm.