Design of 45 degree waveguide isolators

Abstract

Optical waveguide isolators are required in advanced fiber communication systems. The simplest type is the 45°-waveguide-isolator based on magnetooptic channel waveguides. The problem of phase mismatch can be solved simply by choosing a proper angle of preferably 22.5° between the input polarization and the direction of the TE polarization of the waveguide. Mode coupling in this configuration is analysed using "coupling tracks" on the Poincar sphere. First experiments demonstrate that more than 30dB isolation is feasible in practical devices. From these results, design rules for 45°waveguide isolators are obtained.