Fabrication Techniques for Geodesic Lenses in Lithium Niobate

Progress in the evaluation of fabrication techniques for geodesic lenses is reported. These are required for the development of an integrated optical spectrum analyzer using titanium-diffused waveguides in lithium niobate. Lenses have been designed by the method of Sottini, Russo, and Righini, with some essential modifications to the profile to bridge over regions of extreme curvature. The fabrication techniques under investigation are ultrasonic impact grinding, diamond tool grinding, and diamond turning, followed by polishing with large area flexible tools or small pads under positionprogrammed control. Diamond turning appears to produce an accurate profile, with a surface finish approaching the required degree of smoothness, although polishing is still necessary. Methods of measuring lens profiles and assessing surface finish are described. Details of measurements of in-plane scatter levels are given also.