Multiple focus lens, an optical head apparatus and an optical information recording-reproducing apparatus

• US 5,986,779 A
• Filed: 08/12/1996
• Issued: 11/16/1999
• Est. Priority Date: 08/18/1995
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Komma, Yoshiaki, Yamagata, Michihiro, Tanaka, Yasuhiro, Mizuno, Sadao
• Primary Examiner(s): Henry, Jon W.
• Assistant Examiner(s): Schuberg, Darren E.
• Application Number:
  US08/695,397
• Time in Patent Office: 1,191 Days
• Field of Search: 359/16, 359/19, 359/566, 359/570, 365/215, 365/216, 369/94, 369/103
• US Class Current: 359/19
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4238 in optical recording or readout devices optical pick-up devices such as for CD, DVD or BD reader or recorder using diffraction optics G11B7/1353
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power
• CPC Class Codes: G11B 2007/0006 adapted for scanning different types of carrier, e.g. CD & DVD
• 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 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/13922 passive

Abstract

Coma of an objective lens occurs depending on the lens-forming condition when plural disks of different substrate thickness are recorded and reproduced. An objective lens according to this invention is not influenced by the coma even if the thickness of the substrates is changed. For this purpose, a diffraction grating whose aberration is corrected is formed on the first side of an aspheric objective lens. Due to this correction, light beams having different diffraction orders, e.g. 0th order diffracted light and +1st order diffracted light, are focused respectively on two kinds of substrates of different thickness. The whole objective lens is tilted to correct its axial coma, and the tilt angle is predetermined to be substantially identical with respect to plural substrates which are different in thickness.

Claims

1. A multiple focus objective lens comprising at least one lens and a diffracting means for focusing light on a surface and whose aberration is corrected so that light beams having various diffracting orders focus respectively on plural substrates of different thickness, the lens being tilted to correct axial coma of the lens towards said plural substrates, the tilt angles of said lens with respect to said substrates being substantially the same.

2. The multiple focus objective lens according to claim 1, which focuses 0th order diffracted light diffracted by said diffracting means on an information recording surface of a first substrate and focuses +1st order diffracted light diffracted by said diffracting means on an information recording surface of a second substrate which is different in thickness from said first substrate, and meets the requirement,

3. The multiple focus objective lens according to claim 1, which focuses 0th order diffracted light diffracted by said diffracting means on the information recording surface of the first substrate and focuses +1st order diffracted light diffracted by said diffracting means on the information recording surface of the second substrate different from said first substrate in thickness, and a residual coma ZC meets the requirement,

4. The multiple focus objective lens according to claim 1, wherein said diffracting means is formed on one side of the lens.

5. The multiple focus objective lens according to claim 4, wherein said lens is a singlet having at least one aspheric surface.

6. The multiple focus objective lens according to claim 4, wherein said diffracting means is a conic circular phase grating.

7. The multiple focus objective lens according to claim 1, wherein said diffracting means is formed on a plane substrate.

8. The multiple focus objective lens according to claim 7, whose plane substrate is formed by glass-molding method or resin-molding method.

9. The multiple focus objective lens according to claim 1, wherein said diffracting means is a phase grating.

10. The multiple focus objective lens according to claim 1, wherein focusing is conducted by using the 0th order diffracted light and the +1st order diffracted light respectively toward two kinds of substrates of different thickness.

11. The multiple focus objective lens according to claim 10, which focuses the 0th order diffracted light toward the thicker substrate.

12. The multiple focus objective lens according to claim 10. which focuses the 0th order diffracted light toward the thinner substrate.

13. The multiple focus objective lens according to claim 1, which is a singlet having at least one aspheric surface, and the coma the objective lens has on the axis is generated when the first surface and the second surface of the lens are relatively tilted at 0.05°

.

14. The multiple focus objective lens according to claim 1, which meets the requirements:

space="preserve" listing-type="equation">|fa.sup.2 (1/(fd·

Vd)+1/(fs·

Vs))|<

0.0025

space="preserve" listing-type="equation">Vs=(nλ

-1)/(nλ

(-)-nλ

(+))

space="preserve" listing-type="equation">Vd=λ

/(λ

(-)-λ

(+))

where;

λ

;

design wavelength

λ

(+);

a wavelength 10 nm longer than the design wavelength

λ

(-);

a wavelength 10 nm shorter than the design wavelength

nλ

;

refractive index of lens for the design wavelength

nλ

(+);

refractive index of lens at wavelength which is 10 nm longer than the design wavelength

nλ

(-);

refractive index of lens at wavelength which is 10 nm shorter than the design wavelength

fs;

focal length of the lens defined by the 0th order diffracted light

fd;

focal length of the lens only by diffracting means

fa;

focal length of the lens defined by the +1st order diffracted light.

15. The multiple focus objective lens according to claim 1, in which at least one of the surfaces of the lens is integrated with the diffracting means and is formed by glass-molding method or resin-molding method.

16. An optical head apparatus which comprises a light source, means for focusing the light radiated from the light source on a surface of an information medium, means for separating beams modulated by said information medium, and means for receiving the light modulated by said information medium, wherein said focusing means is a multiple focus objective lens comprising a diffracting means whose aberration is corrected so that light beams having various diffracting orders focus respectively on plural substrates of different thickness, the lens is tilted to correct axial coma of the lens toward said substrates, the tilt angles to said substrates being substantially the same.

17. The optical head apparatus according to claim 16, whose multiple focus objective lens focuses 0th order diffracted light diffracted by the diffracting means on an information recording surface of a first substrate and focuses +1st order diffracted light diffracted by said diffracting means on an information recording surface of a second substrate which is different in thickness from said first substrate, and meets the requirement,

18. The optical head apparatus according to claim 16, whose multiple focus objective lens focuses 0th order diffracted light diffracted by said diffracting means on the information recording surface of the first substrate and focuses +1st order diffracted light diffracted by said diffracting means on the information recording surface of the second substrate different from said first substrate in thickness, and residual coma ZC meets the requirement,

19. An optical information recording-reproducing apparatus which records and reproduces information on plural kinds of recording media of different thickness, by using an optical head apparatus which comprises a light source, means for focusing the light radiated from the light source on a surface of an information medium, means for separating beams modulated by said information medium, and means for receiving the light modulated by said information medium, wherein said focusing means is a multiple focus objective lens comprising a lens and a diffracting means whose aberration is corrected so that light beams having various diffracting orders focus respectively on plural substrates of different thickness, the lens is tilted to correct axial coma of the lens toward said substrates, the tilt angles with respect to said substrates being substantially the same.

20. The optical information recording-reproducing apparatus according to claim 19, whose multiple focus objective lens focuses 0th order diffracted light diffracted by said diffracting means on an information recording surface of a first substrate while focuses +1st order diffracted light diffracted by said diffracting means on an information recording surface of a second substrate different in thickness from said first substrate, and meets the requirement,

21. The optical information recording-reproducing apparatus according to claim 19, whose multiple focus objective lens focuses 0th order diffracted light diffracted by said diffracting means on the information recording surface of the first substrate and focuses +1st order diffracted light diffracted by said diffracting means on the information recording surface of the second substrate of different thickness from said first substrate, and residual coma ZC meets the requirement,