Single objective lens for use with CD or DVD optical disk

Abstract

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.

Description

70

FIG. 9 shows the wavefront error for the diffractive objective of FIG. 8. It is significant that the wavefront error vertical scale is ten times more sensitive than the prior plots.

The wavefront error is essentially zero and the more sensitive scale is needed to see any wavefront error in this plot.

FIG. 10 shows the depth of focus properties of the diffractive objective of FIG. 8. The performance of the 0.45 NA, 780 nm system is better than the prior art. This permits a slightly greater fabrication tolerance margin compared to prior art objective lenses. The 0.60 NA, 650 nm nominal system depth of focus is about +1.0 micrometer. After fabrication tolerances are considered, the depth of focus will be on the order of ±0.7 micrometer. This is equivalent to the depth of focus that can be achieved by a 0.60 NA, 650 nm objective that only operates with a DVD format reader.

FIG. 11 shows an important feature of diffractive surfaces. The percentage of light that is focused by a diffractive surface is wavelength dependent and several different images can be produced in different diffraction orders. The proper choice of the diffractive surface depth will cause essentially all of the energy in one wavelength to be in the image of the preferred first diffraction order. Because the optimum depth is wavelength dependent and the laser diodes operate at 780 nm and 650 nm, not all of the energy in these two wavelengths can be directed into their respective first order images. The depth of the diffractive surface of this invention is, therefore, chosen midway between these two wavelengths at a wavelength value of 715 nm.

FIG. 11 shows that 0.97 of the energy is directed to the respective first order images when this condition is met. The remaining 0.03 of the energy is primarily directed into the zero diffraction order and is distributed over a large area of the optical disk and produces a negligible background signal.

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.

Claims

1. 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 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.

2. The apparatus of claim 1 wherein said lens has first and second surfaces, and said first surface is located closer to said disk support and drive means than said second surface and said diffractive means is carried by said second surface.

3. The apparatus of claim 1 wherein said lens has first and second surfaces, and said first surface is located closer to said disk support and drive means than said second surface and said diffractive means is carried by said first surface.

4. The apparatus of claim 1 wherein said diffractive means provides sufficient correction for spherical aberration and for spherochromatism that said single element objective lens achieves diffraction-limited image quality for both CD and DVD formats.

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 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 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.

6. The apparatus of claim 5 wherein said diffractive means has a predetermined depth to optimize diffraction efficiency for both laser diode wavelengths.

7. The apparatus of claim 6 wherein said first surface is located closer to said disk support and drive means than said second surface and said diffractive means is carried by said second surface.

8. The apparatus of claim 7 wherein said diffractive means provides sufficient correction for spherical aberration and for spherochromatism that said single element objective lens achieves diffraction-limited image quality for both CD and DVD formats.

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 comprising a central aperture zone, an outer aperture zone, and a diffractive surface,

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 surface providing sufficient aspheric surface power for spherical aberration correction, and comprising a positive powered diffractive surface which corrects spherical aberration due to different substrate thickness of the optical disks.

10. The optical disk reader or optical read/write system of claim 9, wherein each diffractive ray, for reading or writing for the different disk formats, has the same diffraction order.

11. The optical disk reader or optical read/write system of claim 10, wherein the same diffraction order is a first diffraction order.

12. The optical disk reader or optical read/write system of claim 9, wherein the diffractive surface has a predetermined depth having an optimum wavelength dependent on a predetermined wavelength between the first wavelength and the second wavelength.

13. The optical disk reader or optical read/write system of claim 9, wherein the diffractive surface is based on a polynomial phase function comprising a non-zero fourth power term which controls spherical aberration correction.

14. The optical disk reader or optical read/write system of claim 9, wherein the diffractive surface diffracts the output beam having the first wavelength and diffracts the output beam having the second wavelength.

15. The optical disk reader or optical read/write system of claim 9, wherein the single element objective lens is a molded cyclic olefin copolymer plastic lens.

16. 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 comprising diffractive surface, 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 lased 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 surface providing sufficient aspheric surface power for spherical aberration correction, and comprising a positive powered diffractive surface which corrects spherical aberration due to different substrate thickness of the optical disks.

17. The optical disk reader or optical read/write system of claim 16, wherein each diffractive ray, for reading or writing for the different disk formats, has the same diffraction order.

18. The optical disk reader or optical read/write system of claim 17, wherein the same diffraction order is a first diffraction order.

19. The optical disk reader or optical read/write system of claim 16, wherein the diffractive surface has a predetermined depth having an optimum wavelength dependent on a predetermined wavelength between the first wavelength and the second wavelength.

20. The optical disk reader or optical read/write system of claim 16, wherein the diffractive surface is based on a polynomial phase function comprising a non-zero fourth power term which controls spherical aberration correction.

21. The optical disk reader or optical read/write system of claim 16, wherein the diffractive surface diffracts the output beam having the first wavelength and diffracts the output beam having the second wavelength.

22. The optical disk reader or optical read/write system of claim 16, wherein the single element objective lens is a molded cyclic olefin copolymer plastic lens.