An integrated optical circuit comprises a first waveguide section of a first material having a first index of refraction, a second waveguide section diffused with a second material, different from the first material, the second waveguide section having a second index of refraction; and a third waveguide section of the first material. A portion of the first waveguide section at a first interface is angled at a first angle and a portion of the second waveguide section is angled at the first angle. A portion of the first waveguide section at a second interface is angled at a second angle and a portion of the third waveguide section is angled at the second angle. The first angle and second angle are selected such that the angle of incidence of light at the first and second interfaces is greater than the Brewster's angle.