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.