1. Field of the Invention
The present invention relates to an optical pickup apparatus which can record information on and read information from a digital video disk (DVD) and a recordable compact disk (CD-R), respectively.
2. Description of the Related Art
Recoding media for recording and reading the information such as using video, audio or data, are a disk, a card, or a tape. Among them, the disk type is chiefly used. Recently, in the field of the optical disk apparatus, a laser disk (LD), a compact disk (CD) and a digital video disk (DVD) have been developed. Such an optical disk includes a plastic or glass medium having a certain thickness along an axial direction to which light is incident, and a signal recording surface on which information is recorded and located on the plastic or glass medium.
So far, a high-density optical disk system enlarges a numerical aperture of an objective lens in order to increase a recording density, and uses a short wavelength light source of 635 nm or 650 nm. Accordingly, the high-density optical disk system can record or read signals on or from a digital video disk, and can also read signals from a CD. However, to be compatible with a recent type of a CD, that is, a recordable CD (CD-R), light having a wavelength of 780 nm should be used, due to the recording characteristic of the CD-R recording medium. As a result, using the light beam wavelengths of 780 nm and 650 nm in a single optical pickup becomes very important for compatibility of the DVD and the CD-R. A conventional optical pickup which is compatible with the DVD and the CD-R will be described below with reference to
The light of the 635 nm wavelength emitted from the light source 1 is focused by an objective lens 7 on a signal recording surface in a DVD 8 having a thickness of 0.6 mm. Therefore, the light reflected from the signal recording surface of the DVD 8 contains information recorded on the signal recording surface. The reflected light transmits through the polarization beam splitter 3, and is then incident to a light detector 10 for detecting optical information.
If the finite optical system described above is not used, when the 780 nm wavelength light emitted from the light source 11 is focused on a signal recording surface in the CD-R 9 having 1.2 mm thickness using the above-described objective lens 7, spherical aberration is generated due to a difference in thickness between the DVD 8 and the CD-R 9. In more detail, the spherical aberration is due to a fact that the distance between the signal recording surface of the CD-R 9 and the objective lens 7 is farther than that between the signal recording surface of the DVD 8 and the objective lens 7, along an optical axis. To reduce such a spherical aberration, a construction of a finite optical system including a convergent lens 14 is required. By using a variable aperture 6 to be described later with reference to
The variable aperture 6 of
However, the
An object of the present invention is to provide an optical pickup apparatus which is compatible with a digital video disk and a recordable compact disk by removing a spherical aberration using a phase plate.
To accomplish the above object of the present invention, there is provided an optical pickup apparatus for at least two optical recording media, which are different in distance from an optical pickup to information recording surfaces and uses light beams of 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 the focal point of the objective lens according to the first light beam coincides with the position of the information recording surface in a first optical recording medium having the information recording surface closer to the objective lens;
optical detection means;
means for controlling an optical path so that the light beam emitted from the laser light sources is directed to the objective lens and the light output from the objective lens is directed to the optical detection means; and
phase shift means, coupled between the optical path control means and the objective lens, for shifting the phase of the second light beam proceeding from the optical path control means to the objective lens, thereby reducing the size of a beam spot which is formed on the position of information recording surface in the second optical recording medium having the information recording surface farther from the objective lens by the second light beam focused by the objective lens,
wherein a wavelength of one of the first light and second light beams is used according to the optical recording medium used.
The preferred embodiments are described with reference to the drawings wherein:
Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings.
Referring to
The light beam transmitting the variable aperture 35 transmits through a phase plate 36 (to be described later with reference to
The phase plate 36 is, as shown in
2πn′D/λ′−2πD/λ′=(2m′)π (1)
2πn′D/λ′−2πD/λ′=(2m+1)π (2)
Here, m is an integer, n′ and n denote a refractive index at wavelength λ′ (650 nm) and λ (780 nm), respectively. In the above equations (1) and (2), if m′=3 and m=2, the depth D of the annular groove 361 becomes about 3.9 μm. The phase plate 36 having the annular groove 361 of the depth D phases-shifts the 780 nm wavelength light by 180° and phase-shifts the 650 nm wavelength light by 360° when the two wavelengths proceed to the objective lens 37 from the variable aperture 35.
Thus, the 780 nm wavelength light which is phase-shifted by 180° has a substantially super-resolution effect and passes through an aperture compared with the case when the phase plate 36 is not used. By using the phase plate 36, the size of the light spot formed on the information recording surface in the CD-R 9 is reduced to a degree such that information can be recorded or read on or from the CD-R 9, to thereby remove any spherical aberration.
The phase plate 36 can be modified into a protrusion form having a predetermined width and height protruding outwards from the surface closer to the variable aperture 35. Since such a modification is apparent to one having an ordinary skill in the art who knows the function of the phase plate, the detailed description thereof will be omitted.
The objective lens 37, to which the light transmitting the phase plate 36 is incident, includes an annular shielding portion 371 as shown in
The light beam reflected from the information recording surface of the DVD 8 or CD-R 9 proceeds to a light detection lens 38 from the objective lens 37, and is focussed in the light detector 39 by the light detection lens 38. Thus, the
The annular groove 471 formed in objective lens 47 as shown in
The above-described embodiments have been described with the structure including a variable aperture, a phase plate and an annular shield objective lens. However, using only a phase plate, the spherical aberration due to a disk exchange is reduced and an optical spot appropriate for the CD-R can be formed on the information recording surface.
The above-described embodiments have been described in connection with a infinite optical system which is made by the collimating lens 34. However, the present invention can be applied to a finite optical system which has no collimating lens located between a beam divider and an objective lens, as is apparent to one skilled in the art.
As described above, the optical pickup apparatus according to the present invention uses a phase plate. Accordingly, the present invention can provide an optical pickup which is used compatibly with a DVD and a CD-R with a single objective lens, without using a conventional optical apparatus which creates a problem in a manufacturing process.
While only certain embodiments of the invention have been specifically described herein, it will apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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96-37946 | Aug 1996 | KR | national |
This application is a continuation of U.S. patent application Ser. No. 10/458,321, filed Jun. 11, 2003 and now U.S. Pat. No. 6,985,293, which is a continuation of U.S. patent application Ser. No. 09/516,507, filed Mar. 1, 2000, which issued as U.S. Pat. No. 6,791,933, which is a divisional of U.S. patent application Ser. No. 08/921,386, filed Aug. 29, 1997 and which issued as U.S. Pat. No. 6,222,812, which claims the benefit of U.S. Provisional Patent Application No. 60/025,100, filed Sep. 3, 1996 in the U.S. Patent and Trademark Office and of Korean Application No. 96-37946, filed Aug. 29, 1996 in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference.
Number | Name | Date | Kind |
---|---|---|---|
2233591 | Dulovits | Mar 1941 | A |
3305294 | Alverez | Feb 1967 | A |
3958884 | Smith | May 1976 | A |
4074314 | Velzel et al. | Feb 1978 | A |
4210391 | Cohen | Jul 1980 | A |
4266534 | Ogawa | May 1981 | A |
4340283 | Cohen | Jul 1982 | A |
4501493 | Kubota | Feb 1985 | A |
4545653 | Brenden et al. | Oct 1985 | A |
4566762 | Kato | Jan 1986 | A |
4612437 | Ohsato | Sep 1986 | A |
4631397 | Ohsato et al. | Dec 1986 | A |
4733943 | Suzuki et al. | Mar 1988 | A |
4741605 | Alfredsson et al. | May 1988 | A |
4904856 | Nagahama et al. | Feb 1990 | A |
4918679 | Opheij et al. | Apr 1990 | A |
4929823 | Kato et al. | May 1990 | A |
4938573 | Saito | Jul 1990 | A |
4995714 | Cohen | Feb 1991 | A |
4995715 | Cohen | Feb 1991 | A |
5097464 | Nishiuchi et al. | Mar 1992 | A |
5120120 | Cohen | Jun 1992 | A |
5132843 | Aoyama et al. | Jul 1992 | A |
5142411 | Fiala | Aug 1992 | A |
5153778 | Sasian-Alvarado | Oct 1992 | A |
5161040 | Yokoyama et al. | Nov 1992 | A |
5161148 | Hori et al. | Nov 1992 | A |
5164584 | Wike, Jr. et al. | Nov 1992 | A |
5195072 | Fukui et al. | Mar 1993 | A |
5231624 | Finegan | Jul 1993 | A |
5235581 | Miyagawa et al. | Aug 1993 | A |
5303221 | Maeda et al. | Apr 1994 | A |
5345072 | Hayashi et al. | Sep 1994 | A |
5349471 | Morris et al. | Sep 1994 | A |
5386319 | Whitney | Jan 1995 | A |
5438187 | Reddersen et al. | Aug 1995 | A |
5446565 | Komma et al. | Aug 1995 | A |
5473471 | Yamagata et al. | Dec 1995 | A |
5496995 | Kato et al. | Mar 1996 | A |
5513158 | Ohsato | Apr 1996 | A |
5526338 | Hasman et al. | Jun 1996 | A |
5583843 | Horinouchi | Dec 1996 | A |
5587981 | Kamatani | Dec 1996 | A |
5612942 | Takahashi | Mar 1997 | A |
5615199 | Tatsuno et al. | Mar 1997 | A |
5615200 | Hoshino et al. | Mar 1997 | A |
5638353 | Takahashi | Jun 1997 | A |
5659533 | Chen et al. | Aug 1997 | A |
5665957 | Lee et al. | Sep 1997 | A |
5696750 | Katayama | Dec 1997 | A |
5703856 | Hayashi et al. | Dec 1997 | A |
5703862 | Lee et al. | Dec 1997 | A |
5708638 | Braat et al. | Jan 1998 | A |
5717674 | Mori et al. | Feb 1998 | A |
5724335 | Kobayashi | Mar 1998 | A |
5734512 | Shin et al. | Mar 1998 | A |
5734637 | Ootaki et al. | Mar 1998 | A |
5737300 | Ota et al. | Apr 1998 | A |
5754512 | Komma et al. | May 1998 | A |
5768242 | Juday | Jun 1998 | A |
5777803 | Ju et al. | Jul 1998 | A |
5777973 | Yoo et al. | Jul 1998 | A |
5790503 | Mizuno et al. | Aug 1998 | A |
5796683 | Sumi et al. | Aug 1998 | A |
5815293 | Komma | Sep 1998 | A |
5844879 | Morita et al. | Dec 1998 | A |
5856965 | Tsuchiya et al. | Jan 1999 | A |
5917800 | Choi | Jun 1999 | A |
5930214 | Kasahara et al. | Jul 1999 | A |
5986779 | Tanaka | Nov 1999 | A |
6026065 | Kim et al. | Feb 2000 | A |
6052237 | Opheij et al. | Apr 2000 | A |
6222812 | Yoo et al. | Apr 2001 | B1 |
6272096 | Yoo et al. | Aug 2001 | B1 |
6275461 | Yoo et al. | Aug 2001 | B1 |
6304540 | Yoo et al. | Oct 2001 | B1 |
6363046 | Yoo et al. | Mar 2002 | B1 |
6639889 | Yoo et al. | Oct 2003 | B1 |
6791933 | Yoo et al. | Sep 2004 | B1 |
20030210638 | Yoo et al. | Nov 2003 | A1 |
20050018584 | Yoo et al. | Jan 2005 | A1 |
Number | Date | Country |
---|---|---|
7263552 | Oct 1942 | DE |
0587297 | Mar 1994 | EP |
0747893 | Dec 1996 | EP |
0803867 | Oct 1997 | EP |
508448 | Jun 1939 | GB |
62-73429 | Apr 1987 | JP |
2-118508 | May 1990 | JP |
3-244450 | Oct 1991 | JP |
5-81698 | Apr 1993 | JP |
5-241111 | Sep 1993 | JP |
5-242520 | Sep 1993 | JP |
5-313100 | Nov 1993 | JP |
5-342618 | Dec 1993 | JP |
6-96466 | Apr 1994 | JP |
6-259804 | Sep 1994 | JP |
7-65407 | Mar 1995 | JP |
07-098431 | Nov 1995 | JP |
07-302437 | Nov 1995 | JP |
7-302437 | Nov 1995 | JP |
7-311969 | Nov 1995 | JP |
8-055363 | Feb 1996 | JP |
9-27138 | Jan 1997 | JP |
9-198699 | Jul 1997 | JP |
4-178931 | Jun 1998 | JP |
Number | Date | Country | |
---|---|---|---|
20060033996 A1 | Feb 2006 | US |
Number | Date | Country | |
---|---|---|---|
60025100 | Sep 1996 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 08921386 | Aug 1997 | US |
Child | 09516507 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 10458321 | Jun 2003 | US |
Child | 11259262 | US | |
Parent | 09516507 | Mar 2000 | US |
Child | 10458321 | US |