Integrated magnetooptic cross strip isolator

A bimodal planar waveguide segment of specific length and thickness between two thinner single mode sections can serve as an interferometer. Depending on the phase gain of the two modes in the thick region, these fields can i nterfere destructively or constructively at the transition from the bimodal to the single mode section. We employ this geometry to realize a simple ma gnetooptic isolator configuration, using a wide strip that is etched into a double layer in-plane magnetized magnetooptic film. The magnetization is o riented parallel to the strip; the light traverses the strip perpendicularl y. Then the magnetooptic effect causes the phase velocities of TM polarized waves to be different for opposite directions of light propagation, result ing in a nonreciprocal power transfer across the strip. For a properly sele cted geometry one can expect isolator performance. If the strip width varie s slightly, then adjusting the beam in-coupling position means to change th e distance which the light travels in the two mode segment, This offers a c onvenient tuning possibility, which may be a means to overcome the strict f abrication tolerances that apply usually to interferometric integrated isol ator concepts. (C) 2001 Elsevier Science B.V. All rights reserved,