PPLN ridge waveguides for frequency conversion of high power CW beams

International audienceLiNbO3 has one of the highest quadratic nonlinear optical coefficients that makes it a material of choicefor the development of frequency conversion systems and more generally nonlinear optical functions.This crystal can be periodically poled (PPLN) to allow quasi‐phase matching for various combinationsof wavelengths mixing in its wide transparency window (0.4‐5 μm). In addition, efficient nonlinearconversion can be reached even with moderate power CW beams taking advantage of the lightconfinement provided by LiNbO3‐based optical waveguides. However, waveguides made byconventional fabrication techniques such as titanium in‐diffusion or proton exchange still suffer fromunstable behavior due to photorefractive optical damage especially when visible wavelengths areconcerned. In this study, we present recent developments of ridge PPLN waveguides with promisingcharacteristics even when operating at high average power.More specifically, the design, fabrication and characterization of nonlinear PPLN waveguides forsecond harmonic generation (SHG) of telecommunication wavelengths are presented. Fabrication isbased on wafer bonding, grinding‐polishing steps and carving with use of a precision dicing saw. Thecomponents show efficient SHG with normalized conversion over 200%/W. The componentsperformances will be presented along with their long‐term stability when pumped with Watt‐leveloptical signals. Optical damage threshold of the input face is also investigated to determine themaximum usable power. Undoped and MgO doped LiNbO3 are considered. We will also emphasizethe specificity of the ridge waveguides that allows stable frequency conversion at high power. Theperspectives offered by this specific waveguide geometry will also be tackled