An optical
waveguide isolator for use in an
optical communication system is disclosed. The optical
waveguide isolator comprises a semiconductive light
amplifier structure including a
semiconductor substrate of first
conductivity type having a surface of a layer to be formed thereon, a first cladding layer of first
conductivity type formed on the substrate, an
active layer formed on the first cladding layer, a second cladding layer of the second
conductivity type opposite to first conductivity type, formed on
active layer, a first
electrode formed on the surface of the
semiconductor substrate opposite to the surface to be formed as a layer, and a second
electrode formed on the second cladding layer; the first and the second cladding
layers and the
active layer form an optical
waveguide in which the
light wave propagates. The semiconductive light
amplifier structure further comprises a light absorptive magnetic material layer having light absorption function for the
light wave propagating through the optical waveguide. The magnetic material layer is magnetized so as to have the magnetic-field component in the direction which corresponds to the direction where a magnetic vector of the
light wave vibrates, the waveguide structure body has a nonreciprocity optical characteristic that
effective refractive index changes into the light wave to which the optical waveguide is propagated according to the
magnet-optical effect of the light absorptive magnetic material layer according to the direction of propagation, by the
effective refractive index change in the nonreciprocity, the attenuation of the
first light wave that the optical waveguide is propagated in the first direction caused when the said waveguide is propagated, becomes small more than the attenuation of the second light wave propagated in the second direction opposite to the first direction caused when the said waveguide is propagated.