PURPOSE: To make it possible to couple a magneto-optical optically active layer and an anisotropic double refractive layer in accordance with epitaxy and to provide a plane optical isolator which exhibits an isolator of a high degree by constituting a core layer of two magneto-optical composite layers varying in their respective double refractive characteristics.
CONSTITUTION: A GGG base layer 1 consists of gadolinium-gallium-garnet having a lattice constant of 12.38Å in the entire coordinate direction and a refractive index of n=1.945. More preferably, the base layer is cut in orientation of <110>. An absorption layer 2, a coating layer 3, a waveguide constituting layer 4, a waveguide layer 5 and a buffer layer 6 consist of so-called YIG layers which are substd. with separate specifications. The lattice constants and/or refractive indices and/or Faraday rotations of these layers are managed by desired known methods using adequate substitution elements. As a result, the isolation exhibiting an isolation effect of a high degree is obtd.