Abstract

Optical branching waveguides were first investigated experimentally by Yajima,¹ who observed mode splitting behavior in planar glass waveguide branches. Yajima² and Burns and Milton³ introduced a normal mode analysis of a step transition model to analyze branch behavior. The latter authors pointed out the power dividing limit of steep, symmetric branches, and showed that power transfer in near-symmetric branches was a function of a single parameter. This theoretical approach has recently been further improved and extended to multimode branches,⁴ which support more than two local normal modes. The importance of branching waveguides has been demonstrated by their utilization in various integrated optical modulators and switches. These have included passive branches in interferometers and directional couplers as well as active branches where the splitting ratio is electrically controlled. We report here experimental measurements of splitting ratios in various Ti:LiNbO₃ channel waveguide branches as a function of branch angle and asymmetry. To characterize the diffused channel mode dispersion we utilize a dispersion model based on the effective index method.⁵ We then compare our experimental results with computer calculations for similar, but simpler, planar, homogeneous LiNbO₃ branches. Our results are shown to be generally consistent with theoretical predictions and will provide a guide for future branch design.

© 1980 Optical Society of America