Patent ID: 8705331
Filing Date: 2014-04-22
Classification: G02B,G11B

Abstract:
1. An objective lens for an optical disc drive capable of recording data to and/or reproducing data from three types of optical discs by selectively using one of three light beams which have different wavelengths and are substantially collimated beams, where a thickness of a first optical disc of the three types of optical discs to be used for recording data and/or reproducing data using a first light beam of the three light beams having a wavelength shortest of all the wavelengths of the three light beams is represented by t where the wavelength of the first light beam shortest of all the three light beams is represented by λ where a numerical aperture required for recording data to and/or reproducing data from the first optical disc is represented by NA the objective lens comprising a phase shifting structure on one of surfaces thereof, the phase shifting structure including a plurality of annular refractive surface zones concentrically formed about an optical axis of the objective lens, wherein: the phase shifting structure has a first area for converging the third light beam on a recording surface of the third optical disc; the first area includes steps at boundaries between directly adjacent annular refractive surface zones, the steps comprising at least one first step having a first length in an optical path length toward the first light beam, and the steps further comprising at least one second step having a second length different from the first length in the optical path length toward the first light beam; absolute values of changing amounts in the optical path length by the first and second steps are (i i a diffraction order at which a diffraction efficiency for the third light beam passing through the first step is maximized is represented by a (k+1)-th order; and Δ