Abstract

In the 2× format for second-generation magneto-optical (MO) disks, there are recording tracks next to preformat pits. It has been observed that the MO signals from the tracks adjacent to the preformat pits can be affected. We present numerical modeling results on the effect of a tilted ellipsoid of substrate birefringence on the MO readout signal. Theoretical calculations show that the observed effects can be explained if a certain tilt of the ellipsoid of birefringence exists around the preformat pits.

© 1994 Optical Society of America

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References

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  1. D. Treves, D. S. Bloomberg, “Effect of birefringence on optical memory systems,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 262–269 (1986).
    [Crossref]
  2. I. Prikryl, “Effect of disk birefringence on a differential magneto-optic readout,” Appl. Opt. 31, 1853–1862 (1992).
    [Crossref] [PubMed]
  3. A. B. Marchant, “Retardation effects in magneto-optic readout,” in Optical Mass Data Storage, II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 270–276 (1986).
    [Crossref]
  4. A. Yoshizawa, N. Matsubayashi, “Analysis of optical anisotropy of PC substrate for MO disks and its effect on CNR,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 91–98 (1986).
    [Crossref]
  5. A. Takahashi, M. Mieda, Y. Murakami, K. Ohta, H. Yamaoka, “Influence of birefringence on the signal quality of magneto-optical disks using polycarbonate substrates,” Appl. Opt. 27, 2863–2866 (1988).
    [Crossref] [PubMed]
  6. R. Wimberger-Friedl, “Analysis of the birefringence distributions in compact disks of polycarbonate,” Polym. Eng. Sci. 30, 813–820 (1990).
    [Crossref]
  7. H. Fu, S. Sugaya, J. K. Erwin, M. Mansuripur, “Measurement of birefringence for optical recording disk substrates,” Appl. Opt. 33, 1938–1949 (1994).
    [Crossref] [PubMed]
  8. H. Fu, S. Sugaya, M. Mansuripur, “Measuring distribution of the ellipsoid of birefringence through the thickness of optical disk substrates,” Appl. Opt. 33, (1994).
    [Crossref] [PubMed]
  9. M. Mansuripur, “Certain computational aspects of vector diffraction problems,” J. Opt. Soc. Am. A 6, 786–805 (1989).
    [Crossref]
  10. 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]
  11. B. E. Bernacki, M. Mansuripur, “An investigation of the effects of substrate birefringence on optical-disk performance,” Appl. Opt. 32, 6547–6561 (1993).
    [Crossref] [PubMed]

1994 (2)

H. Fu, S. Sugaya, J. K. Erwin, M. Mansuripur, “Measurement of birefringence for optical recording disk substrates,” Appl. Opt. 33, 1938–1949 (1994).
[Crossref] [PubMed]

H. Fu, S. Sugaya, M. Mansuripur, “Measuring distribution of the ellipsoid of birefringence through the thickness of optical disk substrates,” Appl. Opt. 33, (1994).
[Crossref] [PubMed]

1993 (1)

1992 (1)

1990 (2)

R. Wimberger-Friedl, “Analysis of the birefringence distributions in compact disks of polycarbonate,” Polym. Eng. Sci. 30, 813–820 (1990).
[Crossref]

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)

1988 (1)

Bernacki, B. E.

Bloomberg, D. S.

D. Treves, D. S. Bloomberg, “Effect of birefringence on optical memory systems,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 262–269 (1986).
[Crossref]

Erwin, J. K.

Fu, H.

H. Fu, S. Sugaya, J. K. Erwin, M. Mansuripur, “Measurement of birefringence for optical recording disk substrates,” Appl. Opt. 33, 1938–1949 (1994).
[Crossref] [PubMed]

H. Fu, S. Sugaya, M. Mansuripur, “Measuring distribution of the ellipsoid of birefringence through the thickness of optical disk substrates,” Appl. Opt. 33, (1994).
[Crossref] [PubMed]

Mansuripur, M.

H. Fu, S. Sugaya, M. Mansuripur, “Measuring distribution of the ellipsoid of birefringence through the thickness of optical disk substrates,” Appl. Opt. 33, (1994).
[Crossref] [PubMed]

H. Fu, S. Sugaya, J. K. Erwin, M. Mansuripur, “Measurement of birefringence for optical recording disk substrates,” Appl. Opt. 33, 1938–1949 (1994).
[Crossref] [PubMed]

B. E. Bernacki, M. Mansuripur, “An investigation of the effects of substrate birefringence on optical-disk performance,” Appl. Opt. 32, 6547–6561 (1993).
[Crossref] [PubMed]

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]

M. Mansuripur, “Certain computational aspects of vector diffraction problems,” J. Opt. Soc. Am. A 6, 786–805 (1989).
[Crossref]

Marchant, A. B.

A. B. Marchant, “Retardation effects in magneto-optic readout,” in Optical Mass Data Storage, II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 270–276 (1986).
[Crossref]

Matsubayashi, N.

A. Yoshizawa, N. Matsubayashi, “Analysis of optical anisotropy of PC substrate for MO disks and its effect on CNR,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 91–98 (1986).
[Crossref]

Mieda, M.

Murakami, Y.

Ohta, K.

Prikryl, I.

Sugaya, S.

H. Fu, S. Sugaya, M. Mansuripur, “Measuring distribution of the ellipsoid of birefringence through the thickness of optical disk substrates,” Appl. Opt. 33, (1994).
[Crossref] [PubMed]

H. Fu, S. Sugaya, J. K. Erwin, M. Mansuripur, “Measurement of birefringence for optical recording disk substrates,” Appl. Opt. 33, 1938–1949 (1994).
[Crossref] [PubMed]

Takahashi, A.

Treves, D.

D. Treves, D. S. Bloomberg, “Effect of birefringence on optical memory systems,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 262–269 (1986).
[Crossref]

Wimberger-Friedl, R.

R. Wimberger-Friedl, “Analysis of the birefringence distributions in compact disks of polycarbonate,” Polym. Eng. Sci. 30, 813–820 (1990).
[Crossref]

Yamaoka, H.

Yoshizawa, A.

A. Yoshizawa, N. Matsubayashi, “Analysis of optical anisotropy of PC substrate for MO disks and its effect on CNR,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 91–98 (1986).
[Crossref]

Appl. Opt. (5)

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)

Polym. Eng. Sci. (1)

R. Wimberger-Friedl, “Analysis of the birefringence distributions in compact disks of polycarbonate,” Polym. Eng. Sci. 30, 813–820 (1990).
[Crossref]

Other (3)

A. B. Marchant, “Retardation effects in magneto-optic readout,” in Optical Mass Data Storage, II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 270–276 (1986).
[Crossref]

A. Yoshizawa, N. Matsubayashi, “Analysis of optical anisotropy of PC substrate for MO disks and its effect on CNR,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 91–98 (1986).
[Crossref]

D. Treves, D. S. Bloomberg, “Effect of birefringence on optical memory systems,” in Optical Mass Data Storage II, R. P. Freese, A. A. Jamberdino, M. de Haan, eds., Proc. Soc. Photo-Opt. Instrum. Eng.695, 262–269 (1986).
[Crossref]

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Figures (18)

Fig. 1
Fig. 1

Assumed pattern of birefringence around the preformat pits: (a) cross-sectional side view showing a tilted ellipsoid near the bottom of the substrate in the vicinity of a pit, (b) top view showing variations along the track of the azimuthal orientation of the tilted ellipsoid in the neighborhood of the pits.

Fig. 2
Fig. 2

Definition of the orientational (Euler) angles of the ellipsoid within a Cartesian coordinate system. Here X is along the track, Y is the radial direction, and Z is perpendicular to the disk surface; θ is the tilt angle of the vertical axis of the ellipsoid from the disk normal, Φ is the azimuth of the tilt, and Ψ is the angle of in-plane rotation of the ellipsoid around Z prior to the tilt. When the in-plane birefringence is zero, the value of Ψ is immaterial; the in-plane birefringence axes are aligned with the track and radial directions when Ψ = 0 or 90°. When θ = 0 the value of Φ is immaterial. The vertical axis of the tilted ellipsoid is in the X, Z plane when Φ = 0, i.e., the tilt is along the track. When Φ = 90° the tilted vertical axis is in the Y, Z plane, i.e., the tilt is in the radial direction.

Fig. 3
Fig. 3

Disk–substrate model for investigation of the effects of substrate birefringence. (a) The 20-μm-thick layer that contains the birefringence of the bulk of the substrate has scaled refractive indices: nr = 1.581, nrnt = 1.6 × 10−3, nrnz = 3.6 × 10−2. The index ellipsoid for the top 19.8 μm of this layer has principal axes that are coincident with the radial, track, and vertical directions. In the bottom 0.2-μm-thick layer the ellipsoid is allowed to tilt. We use this layer in the simulations to represent the bottom 12 μm of the actual substrate, which is presumed to be influenced by the preformat pits. (b) Relief pattern showing the simulated grooved disk surface with three magnetic domains (shown as raised areas) centered on the track. Grooves are trapezoidal with a physical depth of 76 nm (optical depth 0.15 λ0); magnetic domains are circular.

Fig. 4
Fig. 4

Schematic diagram of the simulated readout system. The λ/4 plate is present in some of the simulations and absent in others. The Wollaston prism and the two detectors are mounted rigidly in a module that is free to rotate around the optic axis. Orientation angle η of this detection module relative to the direction of incident polarization is adjusted for maximum output signal.

Fig. 5
Fig. 5

Differential MO signal from an erased track versus the detection module's orientation angle η in the presence of a λ/4 plate. No tilt of the ellipsoid of the substrate has been assumed. The maximum signal ΔS = 5.8 × 10−3 is obtained at η = 30°.

Fig. 6
Fig. 6

Three-dimensional and contour plots of polarization rotation angle θk and ellipticity ∊k at the exit pupil of the objective: (a) θmax = 24.8°, θmin = −36.6°, (b) ∊max = 35.3°, ∊min = −41.8°. The assumed substrate is shown in Fig. 3(a), with the ellipsoid of the bottom layer oriented at θ = 60°, Φ = 45°, Ψ = 0. The values of θk and ∊k in the central region of the aperture are those expected from a normally incident plane wave on a laterally birefringent substrate coated with a MO active layer. Significant departure from these expected values near the rim is due to the interaction between oblique marginal rays and the vertical birefringence of the substrate.

Fig. 7
Fig. 7

Differential MO signals from two erased tracks with opposite magnetizations: (a) without the λ/4 plate in the read path, (b) with the λ/4 plate and with the detection module oriented at η = 30°. The substrate with its coating of a MO layer is shown in Fig. 3(a); the assumed tilt angle of the ellipsoid of the bottom layer is θ = 60°. The abscissa is the azimuthal angle Φ of the 60° tilted ellipsoid of the bottom of the substrate. The two curves in each panel correspond to up and down states of magnetization of the erased tracks. Note that at Φ = 0 and 90° the signals are balanced; the worst imbalance occurs around Φ = ±45°.

Fig. 8
Fig. 8

Differential MO signal for the substrate of Fig. 3(a) and the three-mark pattern of Fig. 3(b): (a) without the λ/4 plate in the read path, (b) with the λ/4 plate and with the detection module oriented at η = 30°. The three curves in (a) and (b) correspond to three different azimuthal settings of the 60° tilted ellipsoid of the bottom of the substrate, i.e., Φ = −45°, 0°, and +45°. The peak-to-valley amplitude of the signal is 3 × 10−3 in (a) and 3.3 × 10−3 in (b); the reductions in signal amplitude compared with the erased tracks of Fig. 7 are due to the small size of the MO marks and their intersymbol interference.

Fig. 9
Fig. 9

Differential MO signals for the substrate of Fig. 3(a) and the three-mark pattern of Fig. 3(b). The ellipsoid of the bottom of the substrate is tilted at θ = 60°, Ψ = 0, and (a) Φ = 0, (b) Φ = 45°, (c) Φ = −45°. The λ/4 plate is absent in all cases and the detection module is oriented at η = 45°. In the return path the beam splitter introduces a phase shift Δϕ between the components of polarization parallel and perpendicular to the incident polarization. In (a), where the azimuthal orientation of the ellipsoid is parallel to the track, the three curves are at the same level and the peak-to-valley signal amplitudes for diiferent Δϕ are 3.3 × 10−3, 3 × 10−3, and 2.6 × 10−3. In (b) and (c), where the azimuth of the ellipsoid is at ±45° to the track, the three curves are no longer coincident, but the signal amplitudes for different Δϕ are nearly the same as those in (a).

Fig. 10
Fig. 10

Differential MO signals from erased tracks on the substrate of Fig. 3(a). The ellipsoid of the bottom of the substrate is oriented at θ = 60°, Ψ = 0; the azimuth of the ellipsoid, Φ, is the variable against which the curves are plotted. The λ/4 plate is absent and the detection module is oriented at η = 45°. In the return path the beam splitter introduces a phase shift Δϕ between the parallel and perpendicular components of polarization. In (a) Δϕ = −10°, and in (b) Δϕ = + 10°. Note that at Φ = 0 and 90° the signals are balanced.

Fig. 11
Fig. 11

Polarization rotation angle θk and ellipticity ∊k at the exit pupil of the objective: (a) θmax = 2.9°, θmin = −2.4°; (b) ∊max = 3.4°, ∊min = −3.6°. The assumed substrate is isotropic, and the MO layer is uniformly magnetized (i.e., erased wide track).

Fig. 12
Fig. 12

Differential MO readout signal for an isotropic substrate and the three-mark pattern of Fig. 3(b). The solid curve is obtained without the λ/4 plate in the read path; the dashed curve shows the signal with the λ/4 plate at the optimum setting of the detection module (η = 36°). The peak-to-valley signal amplitudes are 4.1 × 10−3 and 4.2 × 10−3, respectively.

Fig. 13
Fig. 13

Polarization rotation angle θk and ellipticity ∊k at the exit pupil of the objective: (a) θmax = 2.0°, θmin = −1.0°; (b) ∊max = 1.9°, ∊min = −2.1°. The assumed substrate is that in Fig. 3(a) without any birefringence, and the MO layer is uniformly magnetized (i.e., erased wide track).

Fig. 14
Fig. 14

Differential MO signal for the substrate of Fig. 3(a) without birefringence and the three-mark pattern of Fig. 3(b). The solid curve is obtained without the λ/4 plate in the read path; the dashed curve shows the signal with the λ/4 plate at the optimum setting of the detection module (η = 40°). The peak-to-valley signal amplitudes are 3.4 × 10−3 and 3.5 × 10−3, respectively.

Fig. 15
Fig. 15

Typical distribution of the tilt of the ellipsoid through the thickness of the substrate. For each ellipsoid nr= 1.581, nrnt = 2.7 × 10−5, and nrnz = 6 × 10−4. The tilt angle θ varies through the thickness, as shown, but the azimuth of the tilt is fixed at Φ = 90°. The orientation of in-plane birefringence is also fixed at Ψ = 0. For computational reasons this five-layer structure is incorporated into the bottom 20 μm of the substrate, as in Fig. 3(a), and its birefringence values are correspondingly scaled.

Fig. 16
Fig. 16

Polarization rotation angle θk and ellipticity ∊k at the exit pupil of the objective: (a) θmax = 28.9°, θmin = −28.7° (b) ∊max = 38.4°, ∊min = 38.8°. The assumed substrate is that of Fig. 15, and the MO layer is uniformly magnetized (i.e., erased wide track).

Fig. 17
Fig. 17

Differential MO signal for the substrate of Fig. 15 and the three-mark pattern of Fig. 3(b). The solid curve is obtained without the λ/4 plate in the read path; the dashed curve shows the signal with the λ/4 plate at the optimum setting of the detection module (η = 32°). The peak-to-valley signal amplitudes are 3 × 10−3 and 3.3 × 10−3, respectively.

Fig. 18
Fig. 18

(a) Amplitude and (b) phase of the reflection coefficients for p- and s-polarized beams incident at the interface of a thick MO layer ∊ = −5 + 20i) with an isotropic substrate (n = 1.581). The abscissa is the angle of incidence within the substrate. (To simplify matters, we assumed no off-diagonal elements for the dielectric tensor of the MO layer, i.e., ∊xy = 0.)

Tables (1)

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Table 1 System Parameters and Media Characteristics Used in the Calculations

Equations (2)

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Δ S = ± 2 r r = ± 7.4 × 10 3 ( with λ / 4 plate ) .
Δ S = ± 2 r r cos ( Δ ϕ 1 + Δ ϕ 2 ) = ± 6.2 × 10 3 ( without λ / 4 plate ) .

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