Abstract

A servo system for the correction of disk tilt in optical disk data storage is proposed, and its basic concepts are demonstrated by the use of a static system in which the disk does not spin. Because disk tilt produces primarily coma in the beam focused onto the disk, the system uses a variable coma generator to produce an equal and opposite amount of coma as that caused by the tilted disk. The magnitude and direction of disk tilt are detected by the use of the light reflected from the front facet of the disk substrate.

© 1996 Optical Society of America

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References

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  1. J. Braat, “Read-out of optical discs,” in Principles of Optical Disc Systems, G. Bouwhuis, J. Braat, A. Huijser, J. Pasman, G. van Rosmalen, K. Schouhamer Immink, eds. (Hilger, Boston, 1985), p. 23.
  2. A. B. Marchant, Optical Recording: A Technical Overview (Addison-Wesley, Reading, Mass., 1990), Chap. 7, pp. 174–175.
  3. W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1990), pp. 96–99.
  4. W. T. Welford, Aberrations of Optical Systems (Hilger, Bristol, UK, 1986), pp. 234–235.
  5. diffract© is a commercial program available from MM Research, Inc., Tucson, Ariz. The theoretical basis of this program has been described in the following papers: M. Mansuripur, “Certain computational aspects of vector diffraction problems,” J. Opt. Soc. Am. A 6, 786–805 (1989); M. Mansuripur, “Analysis of multilayer thin-film structures containing magneto-optic and anisotropic media at oblique incidence using 2 × 2 matrices,” J. Appl. Phys. 67, 6466–6475 (1990).
    [CrossRef]
  6. R. E. Gerber, M. Mansuripur, “Effects of substrate birefringence and tilt on the irradiance and phase patterns of the return beam in magneto-optical data storage,” Appl. Opt. 34, 4780–4787 (1995).
    [CrossRef] [PubMed]
  7. International Organization for Standardization (ISO), “Report of Joint Technical Committee 1/Subcommittee 23,” Doc. JTC1/SC23 JTC1/SC23 (International Organization for Standardization, Geneva, Switzerland, 1992), p. 14.

1995

1989

Braat, J.

J. Braat, “Read-out of optical discs,” in Principles of Optical Disc Systems, G. Bouwhuis, J. Braat, A. Huijser, J. Pasman, G. van Rosmalen, K. Schouhamer Immink, eds. (Hilger, Boston, 1985), p. 23.

Gerber, R. E.

Mansuripur, M.

Marchant, A. B.

A. B. Marchant, Optical Recording: A Technical Overview (Addison-Wesley, Reading, Mass., 1990), Chap. 7, pp. 174–175.

Smith, W. J.

W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1990), pp. 96–99.

Welford, W. T.

W. T. Welford, Aberrations of Optical Systems (Hilger, Bristol, UK, 1986), pp. 234–235.

Appl. Opt.

J. Opt. Soc. Am. A

Other

J. Braat, “Read-out of optical discs,” in Principles of Optical Disc Systems, G. Bouwhuis, J. Braat, A. Huijser, J. Pasman, G. van Rosmalen, K. Schouhamer Immink, eds. (Hilger, Boston, 1985), p. 23.

A. B. Marchant, Optical Recording: A Technical Overview (Addison-Wesley, Reading, Mass., 1990), Chap. 7, pp. 174–175.

W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1990), pp. 96–99.

W. T. Welford, Aberrations of Optical Systems (Hilger, Bristol, UK, 1986), pp. 234–235.

International Organization for Standardization (ISO), “Report of Joint Technical Committee 1/Subcommittee 23,” Doc. JTC1/SC23 JTC1/SC23 (International Organization for Standardization, Geneva, Switzerland, 1992), p. 14.

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Figures (11)

Fig. 1
Fig. 1

Schematic diagram of the experimental setup used to photograph both the focused spot at the rear surface of the optical disk and the irradiance distribution at the exit pupil of the objective lens.

Fig. 2
Fig. 2

Schematic diagram showing the method of detecting the amount of disk tilt. The reflected spot from the front surface of the disk is reimaged onto a quadrant detector.

Fig. 3
Fig. 3

Schematic diagrams of three possible schemes for maintaining a constant distance between the objective and the lens that images the front-facet reflection onto the quadrant detector. Each scheme that is shown should be incorporated into the movable part of a split head.

Fig. 4
Fig. 4

Calculated pictures of the focused spot at the rear surface of the optical disk (upper rows) and the corresponding irradiance distribution at the exit pupil of the objective lens (lower rows). From left to right, the amounts of third-order coma are 0, 0.2, 0.4, 0.6, 0.8, and 1.0 waves. The direction of the disk tilt is about an axis that is (a) parallel and (b) perpendicular to the grooves; these cases are commonly known as radial tilt and tangential tilt respectively. The wavelength of the incident light is 0.633 μm, the NA of the objective is 0.6, the pupil diameter of the objective is 4 mm, and the track pitch of the disk is 1.15 μm.

Fig. 5
Fig. 5

Close-up of the system used in measuring the effects of disk tilt on the focused spot and the irradiance distribution at the exit pupil of the objective lens, in the absence of any correction.

Fig. 6
Fig. 6

Measured focused spot at the rear surface of the optical disk (upper rows) and the corresponding irradiance distribution at the exit pupil of the objective lens (lower rows). From left to right, the amounts of uncorrected disk tilt are 0, 2.5, 5, 7.5, and 10 mrad, corresponding to amounts of third-order coma of 0, 0.2, 0.4, 0.6, and 0.8 waves. The direction of the disk tilt is about an axis that is (a) parallel and (b) perpendicular to the grooves; these cases are commonly known as radial tilt and tangential tilt, respectively. The wavelength of the incident light is 0.633 μm, the NA of the objective is 0.6, the pupil diameter of the objective is 4 mm, the thickness of the substrate is 1.2 mm, and the track pitch is 1.15 μm.

Fig. 7
Fig. 7

Close-up of the optical disk system that shows the effects of the tilt-correction module on the focused spot and the irradiance distribution at the exit pupil of the objective lens.

Fig. 8
Fig. 8

Measured focused spot at the rear surface of the optical disk (upper rows) and the corresponding irradiance distribution at the exit pupil of the objective lens (lower rows). In all pictures, the disk is tilted by 7.5 mrad. From left to right, the tilt of the corrector plate is 0, 3.75, 7.5, and 11.25 mrad. The directions of both the disk tilt and the corrector-plate tilt are about an axis that is (a) parallel and (b) perpendicular to the grooves. The wavelength of the incident light is 0.633 μm, the NA of the objective is 0.6, the pupil diameter of the objective is 4 mm, the track pitch of the disk is 1.15 μm, and the thicknesses of both the disk and the corrector plate are 1.2 mm.

Fig. 9
Fig. 9

Schematic diagram showing the geometry involved in the calculations of the wave-front aberrations that are due to a tilted plane-parallel plate. The exit pupil of the focusing lens is located in the xy plane, and the disk is tilted by α in the positive y direction.

Fig. 10
Fig. 10

Normalized pupil coordinates. Note that these are the coordinates generally used in geometric optics and are not the standard set of cylindrical coordinates.

Fig. 11
Fig. 11

Sign convention for the wave-front aberration W.

Tables (1)

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Table 1 Common Aberrations and Their Contributions to the Total Wave-Front Aberration W(ρ, θ) Caused by Optical Disk Tilt

Equations (2)

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α corr α disk = ( f corr f obj ) 3 t disk t corr ,
W ( ρ , θ ) = W 00 + W 20 ρ 2 + W 11 ρ cos θ + W 40 ρ 4 + W 31 ρ 3 cos θ + W 22 ρ 2 cos 2 θ + W 60 ρ 6 + W 51 ρ 5 cos θ + W 42 ρ 4 cos 2 θ + W 33 ρ 3 cos 3 θ + .

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