Abstract: An optical isolator, which is small in size, light in weight and simple in manufacture, includes a Faraday element (1). The optical isolator also includes polarization films (2a, 2b) formed on a light incident surface and light emitting surface of the Faraday element. The Faraday element rotates a polarization plane of incident light by an angle approximately equal to 45.degree.. The optical isolator also includes a magnetic field applying mechanism (3) for applying a magnetic field to the Faraday element. Each of the polarization films (2a, 2b) includes a thin film made of a conductive material. The polarization films form unidirectional grating with an interval not greater than one tenth of the wavelength of light. One of the polarization films (2b) formed on the light emitting surface makes, in a plane perpendicular to an optical axis, an angle with respect to the other polarization film (2a) formed on the light incident surface, the angle which is approximately equal to 45.degree.

Abstract: A polarization-independent optical isolator comprises three Faraday rotators and four birefringent elements. An optical arrangement of these elements is determined on the basis of the appropriate values derived from the analysis for polarization-independency. A transmission loss characteristic, which is most important in practical use of the optical isolator, is maintained at an excellent level even in presence of variation in temperature and wavelength and in presence of fluctuation in working precision. Deterioration of various isolator properties can be avoided.