Efficient second‐harmonic generation in three‐dimensional LiNbO3 optical waveguide

Highly efficient second‐harmonic generation using a titanium in‐diffused LiNbO3 three‐dimensional optical waveguide was performed with the cw Nd : YAG laser at 1.064‐μm wavelength. The phase‐matching condition to convert the TE00 fundamental frequency to the TM00 or TM20 second harmonic was demonstrated by adjusting the crystal temperature. The conversion efficiency is 1.5×10−4 at 2‐mW fundamental input power under the phase‐matching condition. By using a low‐loss LiNbO3 optical waveguide, equipped with highly reflective cavity mirrors on the input and output surfaces, parametric oscillation is expected.