Δn=0.22 birefringence measurement by surface emitting second harmonic generation in selectively oxidized GaAs/AlAs optical waveguides

We have measured the birefringence enhancement due to lateral selective oxidation of AlAs in GaAs/AlAs optical waveguides. The birefringence was measured by imaging the surface-emitted second harmonic generated by the nonlinear interaction of counterpropagating TE and TM modes. In a waveguide containing a single AlAs layer the birefringence is enhanced from Δn=0.017 (before oxidation) to Δn=0.038 (after oxidation). In an oxidized multilayer GaAs/AlAs waveguide, a birefringence as high as Δn=0.22 is measured. This birefringence is sufficient to phase-match the difference frequency generation of 3–5 μm infrared radiation from two near-infrared pumps.