An optical waveguide structure comprises a nonlinear optical waveguide, straight segments in the nonlinear optical waveguide, and curved segments in the nonlinear optical waveguide. The nonlinear optical waveguide comprises a nonlinear optical material having a second order nonlinear coefficient for a nonlinear optical process in which the second order nonlinear coefficient changes with a direction of light propagation. The straight segments in the nonlinear optical waveguide are oriented such a nonlinear optical interaction with light generation that occurs with an overall constructive manner within the nonlinear optical waveguide in response to a light traveling though the nonlinear optical waveguide. The curved segments have a 90 degree bend, wherein the curved segments connect the straight segments to each other within in the nonlinear optical waveguide.