Optical pickup using an optical phase plate and which is compatible with optical recording media of dirrerent types

• US 20030210638A1
• Filed: 06/11/2003
• Published: 11/13/2003
• Est. Priority Date: 08/29/1996
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Yong Hoon, Kim, Tae Kyung, Cho, Kun Ho, Park, No Kyong, Chung, Chong Sam, Choi, Hyun Seob, Yoo, Jang Hoon, Lee, Chul Woo, Seong, Pyong Yong
• Granted Patent: US 6,985,293 B2
• Time in Patent Office: Days
• US Class Current: 369/112.08
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0057 in the form of a laser diode array, e.g. laser diode bar semiconductor laser arrays with beam combining arrangement H01S5/4012
• CPC Class Codes: G02B 27/0944 Diffractive optical elements, e.g. gratings, holograms gratings per se G02B5/18; holograms used as optical elements per se G02B5/32
• CPC Class Codes: G11B 2007/0006 adapted for scanning different types of carrier, e.g. CD & DVD
• CPC Class Codes: G11B 7/12 Heads, e.g. forming of the optical beam spot or modulation of the optical beam disposition or mounting of head elements within housing or with provision for moving of light source, optical beam or detector, irrelevant to the transducing method G11B7/08 ; modulating lasers H01S3/10; controlling the intensity, colour, phase, polarisation or direction of light beams arriving from an independent light source, e.g. switching gating or modulating G02F1/00
• CPC Class Codes: G11B 7/127 Lasers; Multiple laser arrays lasers per se H01S
• CPC Class Codes: G11B 7/1275 Two or more lasers having different wavelengths
• 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 7/1356 Double or multiple prisms, i.e. having two or more prisms in cooperation
• CPC Class Codes: G11B 7/1367 Stepped phase plates
• CPC Class Codes: G11B 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/139 Numerical aperture control means
• CPC Class Codes: G11B 7/13922 passive

Abstract

An optical pickup apparatus having compatibility with a recodable compact disk (CD-R) and a digital video disk (DVD), which uses a wavelength of one of a first light beam and a second light beam according to the recording medium to be used. In the optical pickup apparatus, laser light sources emit a first light beam having a relatively shorter wavelength for the DVD and a second light beam having a longer wavelength for the CD-R, respectively. An objective lens has a predetermined focal length in accordance with the position of an information recording surface in the DVD. An optical path control unit controls the path of light beams so that the light beam emitted from one of the laser light sources is directed to the objective lens and the light output from the objective lens is directed to the optical detection unit. A phase shift unit which is located between the optical path control unit and the objective lens, shifts the phase of the second light proceeding from the optical path control unit to the objective lens, to thereby reduce the size of a beam spot which is formed on a position of the information recording surface in the CD-R.

Claims

1. An optical pickup apparatus for at least two optical recording media, which are different in distance from an optical pickup to an information recording surface and using light beams having different wavelengths for recording and reading information, the optical pickup apparatus comprising:

a plurality of laser light sources for emitting a first light beam having a relatively shorter wavelength and a second light beam having a relatively longer wavelength, respectively;

an objective lens having a predetermined focal length, in which a focal point of said objective lens according to the first light beam coincides with a position on the information recording surface in a first optical recording medium wherein the information recording surface is closer to said objective lens;

means for optical detection;

means for controlling an optical path so that at least one of the first and second light beams emitted from one of the laser light sources is directed to said objective lens and light output from said objective lens is directed to said optical detection means; and

means for phase shifting, located between said optical path control means and said objective lens, for shifting the phase of the second light beam proceeding from said optical path control means to said objective lens, thereby reducing a size of a beam spot which is formed on the position of the information recording surface in the second optical recording medium having the information recording surface which is positioned farther from said objective lens by the second light beam focussed with said objective lens,

wherein the wavelength of one of the first and second light beams is chosen according to the optical recording medium to be used.

2. The optical pickup apparatus according to claim 1, wherein said phase shift means is a phase plate including two regions which have different thicknesses from a surface of said phase plate which is disposed relatively farther from said optical path control means.

3. The optical pickup apparatus according to claim 2, wherein said two regions include a region having a thin thickness of said phase plate is a portion for shifting the phase of the second light beam, and includes a groove, having a predetermined width and depth which is concave inwards from the surface of said phase plate relatively closer to said optical path control means.

4. The optical pickup apparatus according to claim 3, wherein said region having said thin thickness has a shape of concentric circles with respect to an optical axis of said objective lens.

5. The optical pickup apparatus according to claim 3, wherein said groove has an optical depth for phase-shifting the first light by a degree of 360 and phase-shifting the second light by a degree of 180.

6. The optical pickup apparatus according to claim 2, wherein a region having a thick thickness of said phase plate is a portion for shifting the phase of the second light beam, and includes a protrusion having a predetermined width and height which is protruded outwards from the surface of said phase plate relatively closer to said optical path control means.

7. The optical pickup apparatus according to claim 6, wherein said region of thick thickness has a shape of concentric circles with respect to an optical axis of said objective lens.

8. The optical pickup apparatus according to claim 6, wherein said protrusion has an optical height for phase-shifting the first light beam by a degree of 360 and phase-shifting the second light beam by a degree of 180.

9. The optical pickup apparatus according to claim 2, wherein said phase plate is fabricated by one of etching, injection and molding operations.

10. The optical pickup apparatus according to claim 1, wherein said phase shift means is fabricated by etching a groove having a predetermined width and depth, which is concave inwards from the surface of said objective lens relatively closer to said optical path control means.

11. The optical pickup apparatus according to claim 1, wherein said phase shift means has a shape of a protrusion having a predetermined width and height, which is protruded outwards from the surface of said phase plate relatively closer to said optical path control means.

12. The optical pickup apparatus according to claim 1, wherein said phase shift means has a same curvature as that of said objective lens and is to be coupled with a surface of said objective lens which is relatively closer to said optical path control means.

13. The optical pickup apparatus according to claim 1, wherein said objective lens has a small size of structure, in which one of the first and second light beams is appropriately selected and other components are consistently used whenever one optical recording medium is changed to the other optical recording medium.

14. The optical pickup apparatus according to claim 1, wherein one of said laser light sources and said optical detection means are integrated as a single unit.

15. The optical pickup apparatus according to claim 1, further comprising means for varying an aperture which is located between said optical path control means and said phase shift means, having a first region for transmitting both of the first and second light beams entered from said optical path control means and a second region for transmitting only the second light beam entered therefrom, wherein the first and the second regions have a same optical axis as that of said objective lens.

16. The optical pickup apparatus according to claim 15, wherein the second region of said variable aperture means includes a diffraction grating pattern.

17. The optical pickup apparatus according to claim 15, wherein said phase shift means and said variable aperture means are constructed as a single unit in which said phase shift means is formed within the first region of said variable aperture means.

18. The optical pickup apparatus according to claim 15, wherein said objective lens comprises at least one annular shielding portion for shielding a part of light which is transmitted via the first region.

19. The optical pickup apparatus according to claim 18, wherein said phase shift means and said variable aperture means are constructed as a single unit in which said phase shift means is formed within the first region of said variable aperture means.

25. The optical pickup apparatus according to claim 3, wherein the depth of said groove is determined by the equations:

2π

n′

d/λ

′

−

2π

d/λ

′

=(2m′

)π

, and 2π

nd/λ

−

2π

d/λ

=(2m+1)π

,

wherein m is an integer, and n′ and

n denote a refractive index at wavelength λ

′ and

λ

, respectively.

26. The optical pickup apparatus according to claim 10, wherein the depth of said groove is determined by the equations:

2π

n′

d/λ

′

−

2π

d/λ

′

=(2m′

)π

, and 2π

nd/λ

−

2π

d/λ

=(2m+1)π

,

wherein m is an integer, and n′ and

n denote a refractive index at wavelength λ

′ and

λ

, respectively.

20. An optical pickup apparatus for at least two optical recording media, which are different in distance from an optical pickup to an information recording surface and using light beams having different wavelengths for recoding and reading information, the optical pickup apparatus comprising:

a plurality of laser light sources for emitting a first light beam having a relatively shorter wavelength and a second light beam having a relatively longer wavelength, respectively;

an objective lens having a predetermined focal length, in which a focal point of said objective lens according to the first light beam coincides with a position on the information recording surface in a first optical recording medium wherein the information recording surface is closer to said objective lens;

means for optical detection;

means for controlling an optical path so that at least one of the first and second light beams emitted from one of the laser light sources is directed to said objective lens and light output from said objective lens is directed to said optical detection means; and

means for varying the aperture, located between said optical path control means and said objective lens, having a first region for transmitting both of the first and second light beams entered from said optical path control means, and a second region for transmitting only the second light beam entered therefrom, wherein the first and the second regions have a same optical axis as that of said objective lens, and

wherein the wavelength of one of the first and second light beams is chosen according to the optical recording medium to be used.

21. The optical pickup apparatus according to claim 20, wherein the second region of said variable aperture means includes a diffraction grating pattern.

22. The optical pickup apparatus according to claim 20, wherein said objective lens comprises at least one annular shielding portion for shielding a part of light which is transmitted via the first region.

23. The optical pickup apparatus according to claim 22, further comprising means for phase shifting, located between said variable aperture means and said objective lens, for shifting a phase of the second light beam proceeding from said variable aperture means to said objective lens, thereby reducing a size of a beam spot which is formed on a position of the information recording surface in the second optical recording medium having the information recording surface which is positioned farther from said objective lens by the second light beam focussed with said objective lens.

24. The optical pickup apparatus according to claim 23, wherein said phase shift means and said variable aperture means are constructed as a single unit in which said phase shift means is formed within the first region of said variable aperture means.