Optical pickup device

• US 6,618,424 B1
• Filed: 03/23/2000
• Issued: 09/09/2003
• Est. Priority Date: 03/25/1999
• Status: Expired due to Fees

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamada, Masato, Tsuchiya, Yoichi
• Primary Examiner(s): Ip, Paul
• Assistant Examiner(s): Rodriguez, Armando
• Application Number:
  US09/533,975
• Time in Patent Office: 1,265 Days
• Field of Search: 372/101, 372/102, 372/108
• US Class Current: 372/101
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/1378 Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
• CPC Class Codes: G11B 7/1398 Means for shaping the cross-section of the beam, e.g. into circular or elliptical cross-section
• CPC Class Codes: H01S 5/005 Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping H01S5/026, H01S5/18388 take precedence

Abstract

An optical pickup device includes a semiconductor laser, a collimater lens, an optical member, a halfmirror, an objective lens, a collecting lens and a photodetector. The collimator lens collimates a laser beam from the semiconductor laser. The optical member diffracts the laser beam which has been collimated by the collimator lens outward along the direction of the shorter diameter of the laser beam, and emits a laser beam having a prescribed aspect ratio. The halfmirror passes the laser beam from optical member and reflects one half the light reflected from a signal recording surface of an optical disk to the photodetector. The objective lens focuses the laser beam on the signal recording surface. The collective lens collects the laser beam from the halfmirror. The photodetector detects the laser beam. Therefore, the optical pickup device is capable of converting the aspect ratio of the laser beam emitted from the semiconductor laser, and hence it becomes possible to irradiate the optical disk with the laser beam having sufficient power for recording a signal.

Claims

1. An optical pickup device, comprising:

a laser generating a laser beam having an elliptical cross section;

an objective lens focusing said laser beam on an optical recording medium; and

an optical member provided between said laser and said objective lens, diffracting the laser beam from said laser outward along a direction of a shorter diameter of the laser beam to enlarge only said shorter diameter and not to enlarge or contract a larger diameter of the laser beam, so as to convert the laser beam to a beam having a predetermined aspect ratio;

wherein

said optical member includes

a first optical element diffracting said laser beam outward along the direction of the shorter diameter of the beam, and

a second optical element collimating the beam which has been diffracted by said first optical element.

2. The optical pickup device according to claim 1, wherein

said optical member includes a transparent substrate, said first optical element being formed on one main surface of said substrate and said second optical element being formed on the other main surface of said substrate.

3. The optical pickup device according to claim 1, further comprising

a collimator lens provided between said laser and said optical member for collimating the laser beam from said laser.

4. The optical pickup device according to claim 1, wherein

said first optical element includes a hologram lens consisting of a plurality of parallel stripe members each comprising a continuous un-interrupted stripe, a pitch of said stripe members being gradually made narrower outward from the center.

5. The optical pickup device according to claim 4, wherein

said second optical element includes a hologram lens consisting of a plurality of stripe members, pitch of said stripe members being made gradually narrower outward from the center.

9. The optical pickup device according to claim 1, wherein said first optical element diffracts the laser beam only along the direction of the shorter diameter of the beam.

10. The optical pickup device according to claim 1, wherein said second optical element diffracts the laser beam only along the direction of the shorter diameter of the beam.

6. An optical pickup device, comprising:

a laser generating a laser beam having an elliptical cross section;

an objective lens focusing said laser beam on an optical recording medium; and

an optical member provided between said laser and said objective lens, diffracting the laser beam from said laser outward along a direction of a shorter diameter of the beam so as to convert the laser beam to a laser beam having a desired aspect ratio, wherein

said optical member includes

a first optical element diffracting said laser beam outward along the direction of the shorter diameter of the beam, and

a second optical element collimating the laser beam which has been diffracted by said first optical element,

said first optical element includes a hologram lens including a plurality of stripe members, a pitch of said stripe members being gradually made narrower outward from the center; and

wherein

each of said stripe members has an approximately right-angled triangular cross section.

7. The optical pickup device according to claim 6, wherein

each of said stripe members is tapered stepwise.

8. The optical pickup device according to claim 6, wherein

each of said stripe members is tapered smooth.