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Optical pickup used with both DVD and CD
| Details |
Inventors: Ootaki, Sakashi; Iwasaki, Masayuki;
Assignee: Pioneer Electronic Corporation (Tokyo, JP)
Primary Examiner: Huber; Paul W.
Assistant Examiner:
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas, PLLC
An optical pickup of a compatible type which can be switched for a DVD and a CD by a completely electrical control without the need of a mechanical moving device or the like and is suitable for the reduction in size and also has an excellent efficiency in the use of light. A liquid crystal panel of 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 has a transparent electrode having an aperture pattern of a predetermined shape is used and the liquid crystal panel is arranged so that its plane of polarization crosses a plane of polarization of a polarization beam splitter at a predetermined angle. An applied voltage to the transparent electrode is controlled so that the whole surface of the liquid crystal panel functions as a 1/4 wavelength plate during a reproduction operation or a recording operation of the DVD and only the aperture pattern portion functions as a 1/4 wavelength plate during the reproduction operation of the CD. |
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DETAILED DESCRIPTION The present invention has been made to solve above-mentioned problems and it is an object of the invention to provide an optical pickup of a compatible type which can be switched for the DVD and CD only by an electrical control ultimately without the need of a mechanical moving device and which is suited for reduction in size and is also excellent in efficiency of the use of light.
In order to achieve these objectives, the following various features are devised in the present invention.
According to the first aspect of the invention, there is provided an optical pickup comprising at least a laser light source, a beam splitter, and an objective lens, wherein a diaphragm means which can electrically vary an aperture pattern is arranged between the objective lens and the beam splitter and the aperture pattern is switched in accordance with the type of the optical disc to be used.
According to the second aspect of the invention, in the above described optical pickup, the beam splitter is a polarization beam splitter.
A liquid crystal panel of a transmission type which gives a phase difference of a 1/4 wavelength or a wavelength that is an odd number multiple of the 1/4 wavelength to a transmission light and which has a transparent electrode having an aperture pattern of a predetermined shape, is used as a diaphragm means.
The liquid crystal panel is arranged so that its plane of polarization crosses a plane of polarization of the polarization beam splitter at a predetermined angle, and a voltage applied to the transparent electrode is controlled so that the whole surface of the liquid crystal panel functions as a 1/4 wavelength plate when reproduction or recording is performd on an optical disc for the high-density recording and only the aperture pattern portion functions as a 1/4 wavelength plate when the reproduction of the compact disc is performed.
According to the third aspect of the invention, in the optical pickup according to the second aspect of the invention, a plurality of aperture patterns are formed along the radial direction of the disc
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