Abstract

The fabrication of active optical waveguides is one of the most important subjects for integrated optics. LiNbO₃ and LiTaO₃ are among the best available waveguide media for this application because of their excellent properties in electro-, acousto-optic interactions. Optical waveguides in LiNbO₃ and LiTaO₃ have been proposed and demonstrated using various techniques. The first LiNbO₃ waveguide was formed by out-diffusion of Li₂O so that the extraordinary index of refraction increased at the surface.¹ Later, optical waveguides were also formed in LiNbO₃ and/or LiTaO₃ crystals by in-diffusion of transition metal ions,² epitaxial growth by melting³ or by sputtering.⁴ The most promising and widely used method is the diffusion of Ti metal which provides single mode, low-loss (⪝1 dB/cm) waveguides. In addition, the photolithographic technology can be utilized to form sophisticated optical circuits. However, a major problem in waveguide formation by metal in-diffusion is that at high diffusion temperatures, Li₂O escaped from the surface through the out-diffusion process. As a result, there is an unwanted planar waveguide in addition to the waveguides formed by metal in-diffusion. This paper reports a new technique of using organo-metallic solutions as diffusion sources to form single mode waveguides in LiNbO₃. The preliminary experimental results showed that no Li₂O out-diffusion waveguide was formed with this new diffusion process. The technique is expected to work equally well for LiTaO₃ crystals.

© 1978 Optical Society of America