| 摘要 |
<p>A conventional Wollaston prism to be used as a polarization isolating element for detecting magneto-optical signals is not suitable for miniaturization and reduction in thickness, while an ordinary polarizing diffraction grating is problematic in that a zeroth-order light must be used for detection of polarization because the polarization states of plus- and minus-first-order diffracted lights are the same, and thus the symmetry is deteriorated and the noise increases. To solve these problems, the invention provides a diffraction grating having two or more types of media of different refractive indexes, characterized in that there exists among combinations of two of the media a combination of media having the refractive index difference between the media varying depending on the direction of incident polarization, that its shape is such that the boundary line between the media on a cross section perpendicular to a direction along a lattice pattern is periodic in a direction perpendicular to the lattice pattern in a lattice plane, or is periodic while being expanded or reduced in the direction perpendicular to the direction along the lattice pattern in the lattice plane, and that the boundary line does not have a symmetrical plane perpendicular both to the above lattice plane and the above cross section at one local cycle. This diffraction grating is different from the conventional polarizing diffraction grating in that the polarization states of plus- and minus-n-th-order diffracted lights are not the same and thus it is possible to provide reproduced signals of a magneto-optical recording medium on the basis of the difference in quantity between the received lights.</p> |
