Patent EP-2113918-A2 (EP)
Inventor: HIRAI HIDEAKI
IPC: G11B7/09
Filed: 2009-03-13
Abstract: An optical pickup including a light source, a first light focus device that focuses a light beam on a recording surface of a first optical recording medium, a second light focus device that focuses a light beam on a recording surface of a second optical recording medium having a different track pitch from that of the first optical recording medium, a light reception device that receives a reflected light beam from the first optical recording medium and the second optical recording medium, a polarization selective light path splitting device provided between the light source and the first light focus device and the second light focus device that splits an incident light beam incident to the first light focus device and the second light focus device depending on a polarization direction of the incident light beam, a polarization switching device provided between the light source and the polarization selective light path splitting device that switches the polarization direction of an outgoing light beam emitted from the light source depending on which one of the first optical recording medium or the second optical recording medium is targeted, a first diffraction element provided between the polarization selective light path splitting device and the polarization switching device that diffracts a light beam having a polarization direction perpendicular to the polarization direction of the outgoing light beam emitted from the light source and a second diffraction element provided between the polarization selective light path splitting device and the polarization switching device that diffracts a light beam having a polarization direction parallel to the polarization direction of the outgoing light beam emitted from the light source, wherein the first diffraction element has a periodic structure having a pitch equal to or longer than a wavelength of the outgoing light beam emitted from the light source, the periodic structure includes two kinds of sub-wavelength convexo-concave structures having respective pitches shorter than the wavelength of the outgoing light beam emitted from the light source while the two kinds of sub-wavelength convexo-concave structures of the first diffraction element are alternately arranged at right angles to each other, and the filling factors of the two kinds of sub-wavelength convexo-concave structures of the first diffraction element are determined to substantially equalize effective refractive indices of the two kinds of sub-wavelength convexo-concave structures of the first diffraction element with regard to the polarization direction of the outgoing light beam emitted from the light source, and wherein the second diffraction element has a periodic structure having a pitch equal to or longer than a wavelength of the outgoing light beam emitted from the light source, the periodic structure includes two kinds of sub-wavelength convexo-concave structures having respective pitches shorter than the wavelength of the outgoing light beam emitted from the light source while the two kinds of sub-wavelength convexo-concave structures of the first diffraction element are alternately arranged at right angles to each other, and the filling factors of the two kinds of sub-wavelength convexo-concave structures of the second diffraction element are determined to substantially equalize effective refractive indices of the two kinds of sub-wavelength convexo-concave structures of the second diffraction element with regard to a polarization direction perpendicular to the polarization direction of the outgoing light beam emitted from the light source.