Optical pickup used with both DVD and CD

An optical pickup comprising:

• a laser light source;
• a beam splitter;
• an objective lens;
• and
• a liquid crystal panel arranged in an optical path between said beam splitter and said objective lens, which is operative to electrically change an aperture pattern defining at least a size of a light beam passing said liquid crystal panel, whereby said aperture pattern is switchable in accordance with a type of an optical disc to be used;
• and
• wherein an applied voltage to a transparent electrode having said aperture pattern of a predetermined shape is controlled so that the whole surface of said liquid crystal panel functions as a 1/4 wavelength plate when performing a reproducing operation or a recording operation of an optical disc for high-density recording and only said aperture pattern portion functions as a 1/4 wavelength plate when performing a reproduction operation of a compact disc.

An optical pickup comprising:

• a laser light source;
• a polarization beam splitter;
• an objective lens;
• and
• a liquid crystal panel arranged in an optical path between said beam splitter and said objective lens, which can electrically change an aperture pattern defining at least a size of a light beam passing said liquid crystal panel, whereby said aperture pattern is switchable in accordance with a type of an optical disc to be used;
• and
• wherein said liquid crystal panel is a transmission type which gives a phase difference of a 1/4 wavelength or a wavelength that is an odd number multiple of 1/4 wavelength to a transmission light and which has a transparent electrode having said aperture pattern of a predetermined shape;
• said liquid crystal panel being arranged so that its plane of polarization crosses a plane of polarization of said polarization beam splitter at a predetermined angle;
• and
• an applied voltage to said transparent electrode is controlled so that the whole surface of said liquid crystal panel functions as a 1/4 wavelength plate when performing a reproducing operation or a recording operation of an optical disk for high-density recording and only said aperture pattern portion functions as a 1/4 wavelength plate when performing a reproduction operation of a compact disc.