Abstract

In an optical disk drive, it is well known that a tilt of the disk causes an offset in the tracking-error signal (TES). One effect of disk tilt is the introduction of a dc component to the TES, which can be largely corrected by operation of the tracking system at the midpoint between the maximum and the minimum values of the open-loop TES. However, this method of correcting for the dc shift in the TES does not correct for the effect of coma in the focused spot, which leads to track offset. The track offset of a system is defined as the distance between the peak irradiance in the focused spot and the center of the groove when the tracking system is operating at the midpoint between the maximum and the minimum values of the open-loop TES in the presence of disk tilt. Calculations are performed that show the dependence of track offset on various system parameters, including track pitch, wavelength, and numerical aperture and rim intensity of the objective lens, and on the regions of the beam used to generate the TES. The track offsets for several beam-segmentation schemes are calculated for a digital versatile disk that uses push–pull and differential phase tracking. It is shown that for differential phase tracking the value of track offset depends on the mark length.

© 1998 Optical Society of America

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References

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  1. A. B. Marchant, “Focus and tracking servos,” in Optical Recording: A Technical Overview (Addison-Wesley, Reading, Mass., 1990), pp. 171–181.
  2. 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, Mass., 1985), pp. 7–38.
  3. R. E. Gerber, “The irradiance distribution at the exit pupil of the objective lens in optical disk data storage,” Ph.D. dissertation (University of Arizona, Tucson, Ariz., 1995).
  4. C. L. Bartlett, D. Kay, M. Mansuripur, “Computer simulations of effects of disk tilt and lens tilt on push–pull tracking error signal in an optical disk drive,” Appl. Opt. 36, 8467–8473 (1997).
    [CrossRef]
  5. 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. M. Mansuripur, “Certain computational aspects of vector diffraction problems,” J. Opt. Soc. Am. A 6, 786–805 (1989); erratum 10, 382–383 (1993).

1997 (1)

1990 (1)

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]

1989 (1)

Bartlett, C. L.

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, Mass., 1985), pp. 7–38.

Gerber, R. E.

R. E. Gerber, “The irradiance distribution at the exit pupil of the objective lens in optical disk data storage,” Ph.D. dissertation (University of Arizona, Tucson, Ariz., 1995).

Kay, D.

Mansuripur, M.

Marchant, A. B.

A. B. Marchant, “Focus and tracking servos,” in Optical Recording: A Technical Overview (Addison-Wesley, Reading, Mass., 1990), pp. 171–181.

Appl. Opt. (1)

J. Appl. Phys. (1)

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]

J. Opt. Soc. Am. A (1)

Other (3)

A. B. Marchant, “Focus and tracking servos,” in Optical Recording: A Technical Overview (Addison-Wesley, Reading, Mass., 1990), pp. 171–181.

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, Mass., 1985), pp. 7–38.

R. E. Gerber, “The irradiance distribution at the exit pupil of the objective lens in optical disk data storage,” Ph.D. dissertation (University of Arizona, Tucson, Ariz., 1995).

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Figures (8)

Fig. 1
Fig. 1

Schematic diagram of the optical head in an optical disk system.

Fig. 2
Fig. 2

(a) Irradiance distribution at the pupil of the objective lens, often called the baseball pattern. (b) Schematic diagram of a push–pull tracking scheme in which the irradiance is summed in the left and the right halves of the baseball pattern and subtracted to generate a TES, S R - S L .

Fig. 3
Fig. 3

Focused spot in the presence of third-order coma W 31 and correcting wave-front tilt W 11, shown relative to the groove geometry in the disk. A higher spot density represents a higher irradiance. Each dashed line passes through the peak irradiance in the focused spot. The four spot diagrams are not to scale and neglect diffraction effects; they are intended only to demonstrate the effects of W 11 and W 31.

Fig. 4
Fig. 4

(a) Regions of the pupil of the objective lens affected when the focused spot is shifted from the center to the edge of a groove. The bright areas show an increase in irradiance, and the dark areas show a decrease in irradiance. (b) Regions of the pupil affected by the presence of coma when the peak irradiance is centered on the groove. The wavelength is 0.635 μm, the NA of the objective lens is 0.6, and the track pitch is 0.74 μm. The patterns of (a) and (b) are independent of pupil apodization.

Fig. 5
Fig. 5

Characteristic ratio W 11/W 31 of the tracking scheme shown in Fig. 2, in which light from the entire pupil is used to generate a push–pull TES. From top to bottom, the five curves correspond to rim intensity values of 30%, 50%, 70%, 90%, and 100%, respectively. The values along the x axes of some common optical disk systems are 1.08 for CD-Read, 0.94 for CD-R, and 1.43 for DVD-R. From the value of W 11/W 31, the numerical value of the TO is calculated from Eqs. (8a, 8b).

Fig. 6
Fig. 6

Six segmentation schemes in which only certain portions of the beam are used for tracking. In all six cases the push–pull tracking signal is given by (S 1 + S 2 - S 3 - S 4), where signals S i are summations of the total optical power incident upon region i. The differential phase TES is obtained from regions 1–4, as well. (The light contained in the gray regions is not used to generate the TES.)

Fig. 7
Fig. 7

Values of TO for the six segmentation schemes (a)–(f) of Fig. 6, used with push–pull tracking. The wavelength is 0.635 μm, the substrate thickness is 0.6 mm, the NA of the objective lens is 0.60, the track pitch is 0.74 μm, and the rim intensity is 70%.

Fig. 8
Fig. 8

Values of TO for the six segmentation schemes of Fig. 6, used with differential phase tracking. The wavelength is 0.635 μm, the substrate thickness is 0.6 mm, the NA of the objective lens is 0.60, the track pitch is 0.74 μm, and the rim intensity is 50%. (a) Mark length of 0.40 μm, (b) mark length of 0.80 μm.

Equations (9)

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W 31 = 1 2 n - 1 2 n 3 NA 3   t λ   δ θ ,
W 31 in waves ,   for CD-R = 0.715 × δ θ   in   degrees .
W 31 in   waves ,   for   DVD-R = 0.676 × δ θ   in   degrees .
D R = 2 NA   δ θ ,
δ x = - λ NA   W 11 ,
δ x = - 0.653 λ NA   W 31 .
W 11 W 31 = - 0.616 RI   of   30 % - 0.644 RI   of   50 % - 0.653 RI   of   70 % 100 % ,
TO CD - R nm / deg   of   disk   tilt = W 11 / W 31 + 0.653 1070   nm / deg .
TO DVD - R nm / deg   of   disk   tilt = W 11 / W 31 + 0.653 730   nm / deg .

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