An optical disk reader or read/write system for CD or DVD formats. first and second laser diodes operating at different wavelengths have their output beams collimated and directed at a single element objective lens, and are then reflected off the disk back through the lens to a photodetector. The single element objective lens has a central aperture zone and an outer aperture zone, the central zone being profiled to operate at a first numerical aperture at approximately 0.45 and the output beam of the first laser diode is confined to the central aperture zone. The outer aperture zone together with the central aperture zone are profiled to operate at a second numerical aperture, for example 0.60 wherein the output beam of the second laser diode has ray fans extending across the full aperture of the single element objective lens. A diffractive is formed on one surface of the single element objective lens and provides sufficient aspheric surface power for spherical aberration correction as well as correction for spherochromatism. The diffractive also provides sufficient correction for spherical aberration and spherochromatism that the single element objective lens achieves diffraction-limited image quality for both CD and DVD formats.
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0. 14. An optical disk reader or optical read/write system capable of operating in different disk formats, each disk format having a different substrate thickness, comprising:
disk support and drive means capable of supporting and driving the different disk formats;
a first laser diode operating with an output beam having a first wavelength;
a second laser diode operating with an output beam having a second wavelength different from the first wavelength; and
a single element objective lens optically positioned between the disk support and drive means on one end and the first and second laser diodes on another end,
the single element objective lens having diffractive means, a central aperture zone, and an outer aperture zone,
the central aperture zone for a first numerical aperture (NA) either directing the output beam of the first laser diode at one disk of the different disk formats when carried by the disk support and drive means or directing together with the outer aperture zone for a second numerical aperture (NA) the output beam of the second laser diode at the other disk of the different disk formats when carried by the disk support and drive means, and
the diffractive means providing sufficient aspheric surface power for spherical aberration correction and providing correction for spherochromatism.
0. 9. An optical disk reader or optical read/write system capable of operating in different disk formats, each disk format having a different substrate thickness, comprising:
disk support and drive means capable of supporting and driving the different disk formats;
a first laser diode operating with an output beam having a first wavelength;
a second laser diode operating with an output beam having a second wavelength different from the first wavelength; and
optical means including a single element objective lens for either directing the output beam of the first laser diode at one disk of the different disk formats when carried by the disk support and drive means or directing the output beam of the second laser diode at the other disk of the different disk formats when carried by the disk support and drive means,
the single element objective lens optically positioned between the disk support and drive means on one end and the first and second laser diodes on another end,
the single element objective lens having a central aperture zone, an outer aperture zone, and diffractive means,
the central aperture zone being profiled to contribute to a first numerical aperture (NA) operation and a first laser diode operation, and to contribute to a second numerical aperture (NA) operation and a second laser diode operation,
the outer aperture zone being profiled to contribute to the second numerical aperture (NA) operation and the second laser diode operation, and
the diffractive means providing sufficient aspheric surface power for spherical aberration correction and providing correction for spherochromatism.
1. An optical disk reader or optical read/write system capable of operating in either a comapct disk (CD) or digital versatile disk (DVD) format, comprising:
disk support and drive means capable of supporting and driving either a compact disk having a disk substrate of thickness Y or a digital versatile disk having a disk substrate of thickness X,
a first laser diode operating with an output beam having a first wavelength,
a second laser diode operating with an output beam having a second wavelength different from said first wavelength,
optical means for either directing the output beam of said first laser diode at a said compact disk when carried by said disk support and drive means or directing the output beam of said second laser diode at a said digital versatile disk when carried by said disk support and drive means,
a single element objective lens optically positioned between said disk support and drive means on one end and said first and second laser diodes on another end,
said single element objective lens having a central aperture zone and an outer aperture zone, said central aperture zone being profiled to operate at a first numerical aperture (NA) and said output beam of said first laser diode being optically confined to said central aperture zone,
said outer aperture zone together with said central aperture zone being profiled to operate at a second numerical aperture (NA) and wherein said output beam of said second laser diode has ray fans extending across the full aperture of said lens, and
diffractive means carried by said single element objective lens, said diffractive means providing sufficient aspheric surface power for spherical aberration correction and providing correction for spherochromatism.
5. An optical disk reader or optical read/write system capable of operating in either a compact disk (CD) or digital versatile disk (DVD) format, comprising:
disk support and drive means capable of supporting and driving either a compact disk having a disk substrate of thickness 2X or a digital versatile disk having a disk substrate of thickness X,
a first laser diode operating with an output beam wavelength of approximately 780 nm,
a second laser diode operating with an output beam wavelength of approximately 650 nm,
optical means for either directing the output beam of said fist laser diode at a said compact disk when carried by said disk support and drive means or directing the output beam of said second laser diode at a said digital versatile disk when carried by said disk support and drive means,
a single element objective lens optically positioned between said disk support and drive means on one end and said first and second laser diodes on another end, said single element objective lens having first and second surfaces, said first surface having an aspheric profile,
said single element objective lens having a central aperture zone and an outer aperture zone, said central aperture zone being profiled to operate at approximately a 0.45 numerical aperture (NA) and said output beam of said first laser diode being optically confined to said central aperture zone,
said outer aperture zone together with said central aperture zone being profiled to operate at approximately a 0.60 numerical aperture (NA) and wherein said output beam of said second laser diode has ray fans extending across the full aperture of said lens, and
diffractive means carried by said single element objective lens, said diffractive means providing sufficient aspheric surface power for spherical aberration correction and providing correction for spherochromatism.
2. The apparatus of
3. The apparatus of
4. The apparatus of
6. The apparatus of
7. The apparatus of
8. The apparatus of
0. 10. The optical disk reader or optical read/write system of
wherein each diffractive ray, for reading or writing for the different disk formats, has the same diffraction order.
0. 11. The optical disk reader or optical read/write system of
wherein the same diffraction order is a first diffraction order.
0. 12. The optical disk reader or optical read/write system of
wherein the diffractive means has a predetermined depth having an optimum wavelength dependent on a predetermined wavelength chosen midway between the first wavelength and the second wavelength.
0. 13. The optical disk reader or optical read/wire system of
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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 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.
Broome, Barry G., Richard, Jenkin A.
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