Overlay-aware design of a wet-etched InP half-ridge polarization rotator with a measured 18-dB extinction ratio.

We report a wet-etched InP half-ridge polarization rotator on a thick generic stack by treating the wet-window overlay as an optical length, not a process allowance. The hybrid-mode angle follows the sum of ridge width and overlay clearance; the conversion length must match the corresponding half-beat. Three devices on one mask measure 14.8-18.0 dB polarization extinction and 1.34-1.47 dB insertion loss at 1550 nm, above the 10-14 dB range of production building blocks. Simulation of the drawn geometry gives 18.5 dB extinction and 1.28 dB insertion loss; the 18.0 dB device agrees within its uncertainty.