Dilute-melt, proton-exchange slab waveguides in LiNbO_3: a new fabrication and characterization method

Abstract

A method of dilute-melt proton exchange employing a mixture of glycerol and KHSO4 with lithium benzoate added is used to fabricate planar waveguides in c -cut LiNbO3 . With this exchange melt system the waveguide refractive-index profiles can be fabricated with a high degree of reproducibility. In contrast with the traditional dilute-melt method, which uses benzoic acid and lithium benzoate, the need for sealed containers during the exchange process can be avoided when the glycerol, KHSO4 , and lithium benzoate system is used for the exchange process. A new characterization method for determining the waveguide refractive-index profile from the measured-mode indexes is introduced. The main advantage of this characterization method compared with other methods is that it also applies to single-mode waveguides. Using the new characterization method, we investigate in detail the relation between waveguide refractive-index change and composition of this glycerol, KHSO4 and lithium benzoate exchange melt system.