Efficient phase-matched second-harmonic generation of blue light in an organic waveguide

Abstract

THE development of materials for the efficient frequency-doubling of low-power semiconductor lasers is a technologically important goal for which several important challenges remain. The ease of processing and high intrinsic optical nonlinearity of organic materials^1,2 makes them attractive for such applications, and it has been demonstrated that molecular-assembly techniques can achieve the macroscopic non-centrosymmetric order required for bulk nonlinear optical activity^3,4. But to achieve efficient power conversion, a promising material must also exhibit low attenuation of light at high power densities, and match phase velocities over relatively long distances for light at the fundamental and second-harmonic frequencies⁵. Here we report the fabrication by Langmuir– Blodgett deposition of a low-loss optical waveguide in which precise control of the film thickness, together with inversion of the nonlinear susceptibility across the film, are used to simultaneously achieve phase matching and improve the optical–field overlap between the propagating (fundamental and second-harmonic) waveguide modes. The resulting structure converts low-power near-infrared laser light efficiently to blue light.