Optical disk apparatus to perform either reproduction or reproduction/recording of each of at least two kinds of optical disks having different substrate thicknesses

To permit reproduction of a CD-R and the reproduction of a DVD in a compatible manner, both the aberration introduced by a substrate of a DVD having a 0.6 mm thickness and the aberration introduced by a substrate of a CD having a 1.2 mm thickness are reduced by a lens shape design where corresponding substrate thicknesses of the inner and outer regions of the objective lens are made different, and providing, in the inner region thereof, a protruding circular phase shifter and, also in a verge of the inner region, an annular phase shifter. The aberration of the objective lens in the CD reproduction was further decreased and the NA was increased up to 0. S, so that the recording of the CD-R was made possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a schematic shape of a DVD/CD-R compatible lens of a conventional example.

FIG. 2 is a diagram showing a wavefront aberration profile for the DVD/CD-R compatible lens of the conventional example.

FIG. 3 is an illustration showing a schematic shape of the object lens according to the present invention.

FIG. 4 is a diagram showing a comparison of the normalized center peak intensities of the CD light spots by the conventional design and according to the present invention as a function of an effective NA for CD-R.

FIG. 5 is a diagram showing design values (in unit of NA) for a radius of a circular region, an inner rim radius of an annular region, and an outer rim radius of the annular region according to the present invention as a function of the effective NA for CD-R.

FIG. 6 is a diagram showing design values for the phase shift of the annular region according to the present invention as a function of the effective NA for CD-R.

FIG. 7 is a diagram showing design values for the optimum substrate thickness of the inner region according to the present invention as a function of the effective NA for CD-R.

FIG. 8 is a diagram showing an example of a calculated wavefront aberration profile of the objective lens according to the present invention.

FIG. 9 is a diagram showing an example of a calculated wavefront aberration profile of a second objective lens according to the present invention.

FIG. 10 is a diagram showing a calculated profile of the conventional CD-R recording light spot.

FIG. 11 is a diagram showing a calculated profile of the conventional CD-R recording light spot focused by the objective lens according to the present invention that gives the wavefront aberration profile of FIG.

8.

FIG. 12 is a diagram showing a calculated profile of a DVD reproducing light spot focused by the conventional objective lens only for DVD.

FIG. 13 is a diagram showing a calculated profile of a DVD reproducing light spot focused by the objective lens according to the present invention that gives the wavefront aberration profile of FIG.

8.

FIG. 14 is a diagram showing a calculated eye pattern for a CD-ROM reproducing signal reproduced with a light spot focused by a conventional objective lens for CD-R shown in FIG.

10.

FIG. 15 is a diagram showing a calculated eye pattern for a CD-ROM reproduced signal reproduced with a light spot focused by the objective lens according to the present invention shown in FIG. 11 (detection NA=0.6).

FIG. 16 is a diagram showing a calculated eye pattern for a CD-ROM reproduced signal reproduced with a light spot focused by the objective lens according to the present invention shown in FIG. 11 (detection NA=0.5).

FIG. 17 is a diagram showing a calculated eye pattern for a DVD-ROM reproduced signal reproduced with a light spot focused by the conventional objective lens for DVD shown in FIG.

12.

FIG. 18 is a diagram showing a calculated eye pattern for a DVD-ROM reproduced signal reproduced with a light spot focused by the objective lens according to the present invention shown in FIG.

13.

FIG. 19 is a diagram showing normalized center peak intensity of the CD-R light spot versus the NA of the radius of the circular region in a design example shown in FIG.

8 and FIG.

9.

FIG. 20 is a diagram showing RMS wavelength aberration in the DVD reproduction versus the NA of the radius of the circular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 21 is diagram showing normalized center peak intensity of the CD-R light spot versus the NA of the inner rim radius of the annular region in a design example shown in FIG.

8 and FIG.

9.

FIG. 22 is a diagram showing the RMS warfront aberration in the DVD reproduction versus the NA of the inner rim radius of the annular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 23 is a diagram showing the normalized center peak intensity of CD-R light spot versus the NA of the outer rim radius of the annular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 24 is a diagram showing the RMS wavefront aberration in the DVD reproduction versus the NA of the outer rim radius of the annular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 25 is a diagram showing the normalized center peak intensity of the CD-R light spot versus the phase shift error in the phase-shifting circular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 26 is a diagram showing the RMS wavefront aberration in the DVD reproduction versus the phase shift error in the phase-shifting circular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 27 is a diagram showing the normalized center peak intensity of the CD-R light spot versus the phase shift error in the phase-shifting annular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 28 is a diagram showing the RMS wavefront aberration in the DVD reproduction versus the phase shift error in the phase-shifting annular region in the design example shown in FIG.

8 and FIG.

9.

FIG. 29 is a diagram showing the normalized center peak intensity of the CD-R light spot versus the deviation of the optimum substrate thickness of the inner region in the design example shown in FIG.

8 and FIG.

9.

FIG. 30 is a diagram showing the RMS wavefront aberration in the DVD reproduction versus the deviation of the optimum substrate thickness of the inner region in the design example shown in FIG.

8 and FIG.

9.

FIG. 31 is a table which summarizes the range of parameters of the optimum lens shape and their tolerances.

FIG. 32 is a diagram showing the normalized center peak intensity of the CD-R light spot versus the deviation of the wavelength thereof in the design example shown in FIG.

8 and FIG.

9.

FIG. 33 is a diagram showing the RMS wavefront aberration in the DVD reproduction versus the deviation of the wavelength thereof in the design example shown in FIG.

8 and FIG.

9.

FIG. 34 is a diagram showing an actual shape of the objective lens in conformity to the design specifications shown in FIG.

8.

FIG. 35 is a diagram showing an optical head with the use of the objective lens according to the present invention.

FIG. 36 is a diagram for explaining operation method of signals from a photodetector.

FIG. 37 is a diagram showing the optical disk apparatus on which the optical head with use of the objective lens is mounted according to the embodiment of the present invention.

1. An optical disk apparatus comprising:

2. An optical disk apparatus comprising: