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Optical pickup device for reproducing discs of two types with different densities by double beam focuses of different sizes
| Details |
Inventors: Choi, Yang-Oh;
Assignee: Daewoo Electronics Co., Ltd. (Seoul, KR)
Primary Examiner: Hindi; Nabil
Assistant Examiner:
Attorney, Agent or Firm: Jacobson, Price, Holman & Stern
A beam generated from a laser light source are reflected by a beam splitter to proceed toward an optical disc. The beam focus onto the optical disc via a selective light-transmitting part installed in front of the optical disc and an objective lens. The beam is totally transmitted through an inner circular portion of the selective light-transmitting part and half transmitted through a peripheral portion of the selective light-transmitting part. The beam transmitted through the inner circular portion forms the larger beam spot on the disc while the beam transmitted through the peripheral portion forms the smaller beam spot, so that spherical aberration to be occurred due to change of the thickness of the optical disc is minimized by using the beam with smaller numerical aperture which has transmitted through the inner circular portion of the selective light-transmitting part. |
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DETAILED DESCRIPTION Therefore, it is an object of the present invention to provide an optical pickup device capable of reproducing discs of two kinds having different densities by forming double beam focuses of different sizes.
To achieve the above object of the present invention, an optical pickup device includes a laser light source for generating laser beam to record or reproducing data of an optical disc, and a beam splitter arranged onto an optical path of the beam generated from the laser light source for partially reflecting and partially transmitting the laser beam.
Also, a selective light-transmitting part has an inner circular part for transmitting the laser beam with a first transmittance and a peripheral portion for transmitting the laser beam with a second transmittance.
Additionally, an objective lens leads the laser beam proceeding toward the optical disc to focus onto the optical disc, and a light-receiving part receives the laser beam reflected from the optical disc.
Preferably, the selective light-transmitting part may be a circular light-transmitting plate of which the peripheral portion is shaped as a ring.
The first transmittance is higher than the second transmittance.
Preferably, the inner circular portion is a totally transmitted one of which the transmittance is 1 and the peripheral portion is a half transmitted one of which the transmittance is 1/2.
A difference between spot sizes focusing on the disc is adjustable by properly regulating an outermost angle of incidence of the laser beam which is transmitted through the inner circular portion of the selective light-transmitting part.
Also, diffraction grating is installed between the laser light source and the beam splitter for controlling tracking and focusing.
As another aspect of the present invention, an optical pickup device includes a hologram device which has a laser light source for generating laser beam, a hologram grating for transmitting the beam emitted from the laser light source and diffracting the beam incident after being reflected from an optical disc, and a light-receiving part for receiving the beam diffracted by the hologram grating
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Optical Systems 
