Robust Light Coupling in a Quadratically Bent Directional Coupler

Bending the axis of an optical directional coupler can result in phase mismatch between the evanescently coupled waveguides. Using a quadratic bending profile, we realize the phase mismatch with a sign flip scheme for robust light coupling between the waveguides. We derive an analytical solution for the coupling scheme and show its robustness against parameter variations. Beam propagation method solution of the scalar wave equation verifies the two-level analysis and the device robustness.