Periodically poled lithium niobate with a 20/spl deg/ fan angle for continuous OPG tuning

Summary form only given.We used standard electric-field poling technique to fabricate a 60-mm long periodically poled lithium niobate crystal with a 20/spl deg/ fan angle. The crystal grating period changed continuously from 25.5 /spl mu/m to 31.25 /spl mu/m across a 15-mm aperture. The 20/spl deg/ fan angle is over six times larger than any PPLN fan gratings previously reported. The last domains on either end of the crystal are oriented at 20/spl deg/ to the y-axis, and are actually oriented closer to the direction of the crystal hexagonal tips than the direction of the hexagonal flat surface. During the poling process, we placed the sample and Plexiglas fixture between crossed polarizers and were able to visualize domain formation in real time. Video footage was acquired and is presented. The fan crystal was polished with opposing 5/spl deg/ wedges on opposite endfaces to prevent oscillation effects from corrupting the single-pass OPG performance.