Excess Loss Reduction in Low Cost Wide Waveguide Gap Polarization Mode Converter

We propose and experimentally demonstrate a segmented waveguide taper (SWT) mode adapter for a polarization mode converter to reduce excess loss induced by a 100- $\mu{\rm m}$ -wide waveguide gap housing a 92- $\mu{\rm m}$ -thick quartz half waveplate. The SWT mode adapter is a combination of periodically segmented waveguide taper and traditional taper formed in a silica-based waveguide. It is proved that this SWT mode adapter requires no vertical tapering process but can enlarge the mode size in both vertical and horizontal directions. Our newly designed SWT mode adapter based on the 0.75%- $\Delta$ silica waveguide is able to reduce the excess loss significantly from 5 dB to less than 1.5 dB.