PURPOSE: To improve adhesive strength with a magneto-optical crystal thin film, to adjust magnitude of a double refraction extending over a wide range, and also to select freely a main axis direction of the double refraction by using a structural double refraction medium as a constituting element of a waveguide type optical isolator.

CONSTITUTION: A medium 8 is vapor-deposited to suitable thickness on the surface of a substrate 10, subsequently, the medium 8 is scraped like a lattice by means of plasma etching, etc., and next, a medium 9 is vapor-deposited, by which a structural double refraction medium is obtained. A main axis direction of a double refraction can be selected to an optional direction by changing a direction of etching. Also, magnitude of the double refraction can be changed extending over a wide range by changing a ratio of thickness of the medium 8 and 9. Also, adhesive strength of this double refraction medium and a magneto- optical crystal thin film is good. A waveguide type isolator having said feature is obtained by laminating an isotropic medium, the magneto-optical crystal thin film and a structural anisotropic medium in this order.