Abstract: An optical isolator for preventing reflection-returned light from entering back into the emitter of an optical system such as an optical fiber communication or an optical disc input/output device, using semiconductor laser. The polarization-independent optical isolator includes a light-emitting side optical fiber having a diameter of a core expanded to give a mode field diameter at an end face of 20 to 50 .mu.m, a light-incident side optical fiber having a diameter of a core expanded to give a mode field diameter at an end face of 20 to 50 .mu.

Abstract: An optical isolator comprising an optical isolator unit having a structure depending on a plane of polarization of incident light, a first optical system for splitting the incident light into two polarized components for incidence on the optical isolator unit, and a second optical system for combining the two polarized components emerging from the optical isolator unit. The optical isolator can thus manifest an excellent effect of isolation without considering the plane of polarization of the incident light.