An optical isolator with a (CeY)3Fe5O12 guiding layer employing TE-TM mode conversion was investigated. The optical isolator consisted of a nonreciprocal polarization rotator and a reciprocal polarization rotator. The reciprocal polarization rotator was realized by inserting a polyimide halfwave plate into a groove in the magnetooptic waveguide. Propagation distances required for the nonreciprocal polarization rotator were calculated at a wavelength of 1.55 μm. Diffraction loss due to the insertion of the half-wave plate was also calculated. The reciprocal polarization rotator integrated with a spot-size converter was proposed for suppressing the diffraction loss. By introducing the spot-size converter for an input facet and an output facet of the half-wave plate, a calculated total insertion loss was reduced to 0.22 dB.
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