| 摘要 |
An optical head apparatus includes a light source and an objective lens focusing a light source light on an optical recording medium. Also included is a light detector receiving a return light, and a variable diffraction device including a first polarized light diffraction grating; and a second polarized light diffraction grating. Provided that a polarizing direction diffracted by the first polarized light diffraction grating is defined as a first polarizing direction and a polarizing direction that is orthogonal to the first polarizing direction and not diffracted by the first polarized light diffraction grating is defined as a second polarizing direction, a ratio obtained from dividing a diffraction efficiency in the second polarizing direction by a diffraction efficiency in the first polarizing direction, of the first polarized light diffraction grating, is 0 to 0.5, and a ratio obtained from dividing a diffraction efficiency in the first polarizing direction by a diffraction efficiency in the second polarizing direction, of the second polarized light diffraction grating, is 0 to 0.5.
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