Topographical electrodes for poling lithium niobate

Periodically poled materials continue to be of great interest due to their applications in both bulk nonlinear optics and all-optical processing systems. Many groups continue to explore alternative techniques to lithographic surface electrodes for defining the domain pattern of the poled crystal. The key objectives of these studies are to reduce the minimum domain size, produce uniformity in the domain structures and improve the cost effectiveness and speed of fabrication. We report progress on an investigation into poling lithium niobate using topographical electrode structures. The structures have been laser machined into the surfaces of 500 μm thick zcut lithium niobate crystals by various laser sources (355 nm YAG laser, 255 nm copper vapour laser, and 800 nm femtosecond laser). We will present a simple electrostatic model of the fields induced by topographical structures which indicates that there is advantages and also limitations in using this technique, in comparison to conventional surface electrodes. Good quality domain structures with periods greater than 20 μm can be routinely fabricated using this method. Moving to thinner wafers, and using insulating and conducting layers in conjunction with laser processing, techniques should enable smaller periods to be achieved while maintaining the advantages of speed and cost effectiveness of using laser processing.