|Publication number||USRE40329 E1|
|Application number||US 10/189,259|
|Publication date||May 20, 2008|
|Filing date||Jul 5, 2002|
|Priority date||May 7, 1998|
|Also published as||US6088322, USRE44397, WO1999057720A1|
|Publication number||10189259, 189259, US RE40329 E1, US RE40329E1, US-E1-RE40329, USRE40329 E1, USRE40329E1|
|Inventors||Barry G. Broome, Jenkin A. Richard|
|Original Assignee||Konica Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (56), Non-Patent Citations (1), Referenced by (1), Classifications (17), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a single objective lens that can be used with either CD optical disks or DVD optical disks. Several different formats of optical disk are known in the prior art. The two most commonly used formats are the CD and the DVD. These two optical disk formats store different data densities; the DVD uses a much smaller track and much smaller “pits” to record a higher data density. The CD (Compact Disk) appears in wide use as both a CD-DA (Company Disk-Digital Audio) and a CD-ROM (Compact Disk-Read Only Memory); the format is identical for these two species. The DVD (Digital Versatile Disk) appears in use as a digital video (movie) storage or an extended computer memory product.
Data records on both CD and DVD formats are in “pits” formed in a reflective surface of the disk. These “pits” are actually in the form of short “trenches” that lie along a track that spirals around the disk surface. The CD “pit” is typically 0.50 micrometer (uM) wide and between 0.83 to 3.05 uM long. The track pitch is 1.6 uM and the depth of the “pit” is 0.20 uM. To achieve higher data density, the DVD “pit” is typically 0.3 uM wide and between 0.40 to 1.5 uM long. The track pitch is 0.74 uM and the “pit” depth is 0.16 uM. The CD can reliably record about 650 MB of digital data whereas the DVD can reliably record about 4.7 GB of digital data on one side of the disk (both sides can be used on a DVD).
The width and depth of the CD “pit” was determined by A early optical fabrication technology which limited the objective lens to 0.45 NA (Numerical Aperture), and by early laser diode technology (a 780 nm emission line). Because cost-effective objective lenses could be made no faster than 0.45 NA (i.e. a relative aperture of f/1.11) and lower wavelength laser diode emission lines were not available, the size of a diffraction-limited laser spot image was limited to 1.0 uM at the Full-Width-Half-Maximum intensity points (FWHM). The CD “pit” depth is chosen to by one-fourth of the laser wavelength (0.20 uM) and the “pit” width is chosen to be about half the laser spot diameter (0.50 uM). This arrangement permits about half of the waterfront in the laser spot to reflect from the bottom of the “pit” and about half of the waterfront to reflect from the surface surrounding the “pit.” The two reflected components are half a wavelength out of phase so they interfere destructively. No signal is, returned to the objective lens when a “pit” is present. When no “pit” is present, the full waterfront reflects from the surrounding surface and light is returned to the objective lens.
This is the digital encoding process for most optical disks.
There are other subtle effects that this encoding process introduces such as diffraction at the edges of the pit, but the interference process is thought to be the principal phenomenon.
The newer DVD format has been enabled by two technology developments; a 650 nm laser diode has become commercially viable and 0.60 NA objective lenses have become cost-effective. The A combination of these two factors produces a diffraction-limited laser spot with 0.64 uM FWHM, so the DVD “pit” width becomes 0.32 uM and the “pit” depth becomes 0.16 uM.
Several optical disk products have been produced in the prior art that combine CD and DVD formats in the same optical reader. In order to achieve this goad, the prior art uses two laser diodes plus two lenses and moves either one set (laser diode plus objective for CD format) or the other set (laser diode plus objective for DVD format) over the disk that is to be read. No prior art single objective design is known that can operate with either the CD or DVD formats.
The invention of this application is a single lens that can operate with either the CD format (with 780 nm laser diode) or with the DVD format (with 650 nm laser diode). No moving parts are required with this invention because the appropriate laser diode can be tuned on electrically and introduced to the objective lens via a dichroic beamsplitter or a grating structure.
The first embodiment of the present invention is shown in greater detail in FIG. 5. This is a molded COC (Cyclic Olefin
Copolymer) plastic lens 20 with aspheric first surface 21 and aspheric second surface 22. This invention uses the fact that the polycaronate disk cover plate 30 varies from 0.6 mm in the DVD format 31 to 1.2 mm in the CD format 32 and that the spherical aberration introduced by the plate is twice as large for the CD format. Concurrently, the objective DVD format NA is 0.60 and introduces nearly 2.4 times the spherical aberration that the CD format 0.45 NA introduces to the system. The spherical aberration of the cover plate and the spherical aberration of the objective, therefore, work in concert for the CD and for the DVD systems to produce similar amounts of system spherical aberration. Although the amount of spherical aberration for the two systems is similar, the distribution of spherical aberration across the aperture of the lens is different for the two systems and this limits the aberration correction to a less than diffraction-limited condition. In addition, the CD and DVD systems operate at different wavelengths and the refractive index of the plastic changes with wavelength in such a way that the distribution of spherical aberration across the lens aperture also changes with wavelength. Optical designers recognize this condition as spherochromatism.
The first embodiment of this invention utilizes the discovery that a single element objective lens can be used for both CD and DVD operation because the amount of spherical aberration for the two systems is similar and can be controlled to nearly diffraction-limited levels by the correct choice of aspheric surface profiles in the central zone 25 and in the outer zone 26 of the objective.
The first surface 21 and second surface 22 shown in
Where sag represents sagittal height, and
the vertex curvatures ρ1 and ρ2 satisfy
The preferred embodiment uses a diffractive surface on one side of the objective. Diffractive surfaces introduce an additional aberration-correction feature that refractive aspheric surfaces cannot provide. Diffractive surfaces change the wavefront differently for different wavelengths. A positive powered diffractive surface bends longer wavelength light more than shorter wavelength light. This is the opposite behavior of a refractive aspheric surface. This new aberration-correction feature permits a single element objective lens to correct most of the spherochromatism that limits the performance of a simple refractive aspheric lens.
Diffractive surfaces are known in the prior art where they are widely used to correct the chromatic aberration of a singlet operating over a board spectral band or to correct the spherical aberration of a singlet over a very narrow spectral band. The use of a diffractive surface to correct sperochromatism spherochromatism of a singlet operating at two different wavelengths is not known in the prior art.
A diffractive surface consists of microscopic grooves in the surface of an optical element. The grooves are widest at the center of the optical element and progressively decrease groove width toward the periphery of the element. The groove width is similar in magnitude to the wavelength of light being used, so the grooves act as a diffraction grating to bend the light. The bending of light is due to diffraction rather than refraction (as produced by Fresnel lenses). Because the groove widths become smaller near the element periphery, the incident wavefront bends more near the edge of the optical element than at the center and the wavefront is therefore focused by diffraction.
Because diffraction is wavelength dependent, the wavefront focusing changes with wavelength to correct chromatic aberration. Because the rate at which the groove widths change can be adjusted to make the surface behave like an aspheric refractive surface, spherical aberration can be corrected.
The first surface 121 shown in
The wavefront error is essentially zero and the more sensitive scale is needed to see any wavefront error in this plot.
Modifications of design may be made without departing from the invention. For example, the diffractive surface may be carried by the lens surface 21 closest to the disk. Various types of collimators and beam-splitters may be used as well as laser diodes of various wavelengths. Various materials may be used for the objective lens, including glass and PMMA.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4344676||Jan 31, 1980||Aug 17, 1982||The Perkin-Elmer Corporation||Single element spherical surfaced optics insensitive to wavelength and temperature|
|US5013133 *||Jun 28, 1989||May 7, 1991||The University Of Rochester||Diffractive optical imaging lens systems|
|US5044706 *||Feb 6, 1990||Sep 3, 1991||Hughes Aircraft Company||Optical element employing aspherical and binary grating optical surfaces|
|US5349471 *||Feb 16, 1993||Sep 20, 1994||The University Of Rochester||Hybrid refractive/diffractive achromatic lens for optical data storage systems|
|US5526338||Mar 10, 1995||Jun 11, 1996||Yeda Research & Development Co. Ltd.||Method and apparatus for storage and retrieval with multilayer optical disks|
|US5629799||Jul 16, 1993||May 13, 1997||Asahi Kogaku Kogyo Kabushiki Kaisha||Chromatic aberration correcting element and its application|
|US5696749||Jun 28, 1996||Dec 9, 1997||Eastman Kodak Company||Dual-wavelength optical recording head utilizing grating beam splitter and integrated laser and detectors|
|US5696750 *||Jun 5, 1996||Dec 9, 1997||Nec Corporation||Optical head apparatus for different types of disks|
|US5703856||Oct 17, 1994||Dec 30, 1997||Matsushita Electric Industrial Co., Ltd.||Optical head and optical data recording and reproducing apparatus having the same|
|US5703862||Dec 26, 1995||Dec 30, 1997||Samsung Electronics Co., Ltd.||Dual focus objective lens with two curvatures for focussing light on two different kinds of disks with different thicknesses|
|US5717674||Jun 27, 1996||Feb 10, 1998||Sanyo Electrics Co., Ltd.||Three-beam generating diffraction grating, transmission type holographic optical element and optical pickup apparatus using the same|
|US5724335 *||Oct 22, 1996||Mar 3, 1998||Konica Corporation||Objective lens for recording and reproducing for use in an optical information recording medium|
|US5757758 *||Dec 9, 1996||May 26, 1998||Konica Corporation||Optical pickup apparatus objective lens and converging optical system for optical pickup and optical disk apparatus|
|US5777970||Feb 21, 1996||Jul 7, 1998||Sanyo Electric Co., Ltd.||Optical disk readout apparatus|
|US5796520||Apr 10, 1996||Aug 18, 1998||Asahi Kogaku Kogyo Kabushiki Kaisha||Chromatic aberration correcting element and its application|
|US5808999||Apr 29, 1997||Sep 15, 1998||Konica Corporation||Optical pickup apparatus and objective lens for optical pickup apparatus|
|US5815293 *||May 31, 1995||Sep 29, 1998||Matsushita Electric Industrial Co., Ltd.||Compound objective lens having two focal points|
|US5835473 *||Jan 15, 1997||Nov 10, 1998||Asahi Glass Company Ltd.||Optical pick-up, optical data recording apparatus and objective lens for optical data recording material|
|US5838496 *||Aug 27, 1996||Nov 17, 1998||Asahi Kogaku Kogyo Kabushiki Kaisha||Diffractive multi-focal objective lens|
|US5838497||Feb 18, 1997||Nov 17, 1998||Asahi Kogaku Kogyo Kabushiki Kaisha||Chromatic aberration correction element and its application|
|US5870369||Feb 13, 1997||Feb 9, 1999||Samsung Electronics Co., Ltd.||Objective lens device including an objective lens and a transparent member having two light control portions and optical pickup using the objective lens device|
|US5880879 *||Aug 26, 1997||Mar 9, 1999||Nikon Corporation||Objective lens system utilizing diffractive optical element|
|US5883744||Feb 18, 1997||Mar 16, 1999||Asahi Kogaku Kogyo Kabushiki Kaisha||Chromatic aberration correcting element and its application|
|US5883747 *||Jun 30, 1997||Mar 16, 1999||Konica Corporation||Recording and/or reproducing optical system and objective lens for optical information recording medium|
|US5883874||Jul 22, 1997||Mar 16, 1999||Daewoo Electronics Co., Ltd.||Optical pickup system for selectively reading a multiple number of optical disks|
|US5889748||Dec 26, 1996||Mar 30, 1999||Hitachi, Ltd.||Object lens and optical head for reproducing data from optical disks in different thickness of substrate|
|US5914822||Feb 9, 1995||Jun 22, 1999||Asahi Kogaku Kogyo Kabushiki Kaisha||Chromatic aberration correcting element and its application|
|US5933401||Jun 5, 1997||Aug 3, 1999||Samsung Electronics Co., Ltd.||Optical pickup having plural optical sources and plural optical detectors|
|US5969862 *||Feb 18, 1997||Oct 19, 1999||Asahi Kogaku Kogyo Kabushiki Kaisha||Chromatic aberration correcting element and its application|
|US5978346||Jan 30, 1998||Nov 2, 1999||Matsushita Electric Industrial Co., Ltd.||Optical head|
|US5986994 *||Dec 12, 1997||Nov 16, 1999||Matsushita Electric Industrial Co., Ltd.||Light pickup of thin type|
|US6043912 *||Mar 30, 1998||Mar 28, 2000||Samsung Electronics Co., Ltd.||Optical pickup compatible with a digital versatile disk and a recordable compact disk using a holographic ring lens|
|US6061324 *||Oct 17, 1997||May 9, 2000||Konica Corporation||Method for recording/reproducing optical information recording medium, optical pickup apparatus, objective lens and design method of objective lens|
|US6084843 *||Mar 16, 1998||Jul 4, 2000||Sony Corporation||Optical recording and reproducing apparatus and method|
|US6118594||Jun 25, 1999||Sep 12, 2000||Asahi Kogaku Kogyo Kabushiki Kaisha||Objective lens for optical pick-up|
|USRE34455||Nov 23, 1988||Nov 23, 1993||Konishiroku Photo Industry Co., Ltd.||Large-aperture single lens with aspherical surfaces|
|DE4323971A1||Jul 16, 1993||Feb 17, 1994||Asahi Optical Co Ltd||CD player objective lens with correction for chromatic aberration - uses cascaded annular surfaces on lens to vary optical path length within lens|
|EP0747893A2||Jun 5, 1996||Dec 11, 1996||Nec Corporation||Optical head apparatus for different types of disks|
|EP0763236A2||Mar 8, 1996||Mar 19, 1997||Philips Electronics N.V.||Device for optically scanning a recording medium|
|EP0824753A1||Feb 25, 1997||Feb 25, 1998||Philips Electronics N.V.||Objective lens and scanning device using such an objective lens|
|EP0824754A1||Feb 25, 1997||Feb 25, 1998||Philips Electronics N.V.||Device for optically scanning a record carrier|
|EP0828244A2||Aug 29, 1997||Mar 11, 1998||Samsung Electronics Co., Ltd.||Optical pickup using an optical phase plate|
|EP0838812A2||Oct 17, 1997||Apr 29, 1998||Konica Corporation||Method for recording/reproducing on/from an optical information recording medium, optical pickup apparatus, objective lens and design method of objective lens|
|EP0844606A1||Nov 18, 1997||May 27, 1998||Matsushita Electric Industrial Co., Ltd.||Objective lens and optical head and optical disk device using the same|
|JPH0682725A||Title not available|
|JPH0713009A||Title not available|
|JPH02183453A||Title not available|
|JPH06215409A||Title not available|
|JPH06242373A||Title not available|
|JPH06250081A||Title not available|
|JPH06259804A||Title not available|
|JPH06331887A||Title not available|
|JPH09179020A||Title not available|
|WO1997033277A1||Feb 25, 1997||Sep 12, 1997||Philips Electronics N.V.||Objective lens and scanning device using such an objective lens|
|WO1997033278A1||Feb 25, 1997||Sep 12, 1997||Philips Electronics N.V.||Device for optically scanning a record carrier|
|WO1999057720A1||May 6, 1999||Nov 11, 1999||Broome Barry G||Single objective lens for use with cd or dvd optical disks|
|1||Gerber R. E. et al.; "Versatile Objective Lens with Adjustable Correction for Different Wavelengths and Substrate Thicknesses for Testing Optical Disks Applied Optics"; vol. 36, No. 11, Apr. 10, 1997, pp. 2414-2402.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US20080204880 *||Aug 5, 2004||Aug 28, 2008||Koninklijke Philips Electronics N.V.||Diffractive Optical Structure with a Liquid Interface|
|U.S. Classification||369/112.26, 369/44.24, 369/94, 369/44.37, 369/118|
|International Classification||G11B7/125, G11B7/135, G11B7/00|
|Cooperative Classification||G11B7/1374, G11B2007/0006, G11B7/1353, G11B7/13922, G11B7/1275|
|European Classification||G11B7/1392C, G11B7/1353, G11B7/1374, G11B7/1275|