Abstract

Polarization dependence of signals from periodic one-dimensional arrays of magnetic domains in magneto-optical (MO) media and crystalline domains in amorphous phase-change (PC) media has been studied by theoretical calculation and experiment. The MO signal in the small-period regime depends on the direction of incident polarization. The relative strength of the E and E signals changes depending on the period of the pattern, the wavelength of the light, and the numerical aperture of the objective lens. For PC media, the reflected signal has similar polarization dependence, but this dependence is weak.

© 2001 Optical Society of America

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References

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  1. H. H. Hopkins, “Diffraction theory of laser read-out systems for optical video discs,” J. Opt. Soc. Am. 69, 4–24 (1979).
    [CrossRef]
  2. J. Pasman, “Vector theory of diffraction,” in Principles of Optical Disc Systems, G. Bouwhuis, ed. (Hilger, Bristol, UK, 1985).
  3. P. Sheng, “Theoretical considerations of optical diffraction from RCA VideoDisc signals,” RCA Rev. 39, 513–555 (1978).
  4. H. Ooki, “Vector diffraction theory for magneto-optical disc systems,” Optik 89, 15–22 (1991).
  5. H. Engstrom, A. B. Marchant, “Polarization considerations in magneto-optical recording,” in Polarization Considerations for Optical Systems II, R. A. Chipman, ed., Proc. SPIE1166, 69–78 (1989).
    [CrossRef]
  6. K. Kobayashi, “Vector diffraction modeling: polarization dependence of optical readout/servo signals,” Jpn. J. Appl. Phys. 32, 3175–3184 (1993).
    [CrossRef]
  7. L. Li, “Rigorous and efficient grating analysis method made easy for optical engineers,” Appl. Opt. 38, 304–313 (1999).
    [CrossRef]
  8. L. Li, “New formulation of the Fourier modal method for crossed surface-relief gratings,” J. Opt. Soc. Am. A 14, 2758–2767 (1997).
    [CrossRef]
  9. DELTA is a diffraction grating program written by Lifeng Li; DIFFRACT is a product of MM Research, Inc., Tucson, Arizona. The theoretical basis of DIFFRACT has been described in the following papers by M. Mansuripur: “Certain computational aspects of vector diffraction problems,” J. Opt. Soc. Am. A 6, 789–805 (1989); “Distribution of light at and near the focus of high-numerical-aperture objectives,” J. Opt. Soc. Am. A3, 2086–2093 (1986); erratum, 382–383 (1993); “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).

1999 (1)

1997 (1)

1993 (1)

K. Kobayashi, “Vector diffraction modeling: polarization dependence of optical readout/servo signals,” Jpn. J. Appl. Phys. 32, 3175–3184 (1993).
[CrossRef]

1991 (1)

H. Ooki, “Vector diffraction theory for magneto-optical disc systems,” Optik 89, 15–22 (1991).

1979 (1)

1978 (1)

P. Sheng, “Theoretical considerations of optical diffraction from RCA VideoDisc signals,” RCA Rev. 39, 513–555 (1978).

Engstrom, H.

H. Engstrom, A. B. Marchant, “Polarization considerations in magneto-optical recording,” in Polarization Considerations for Optical Systems II, R. A. Chipman, ed., Proc. SPIE1166, 69–78 (1989).
[CrossRef]

Hopkins, H. H.

Kobayashi, K.

K. Kobayashi, “Vector diffraction modeling: polarization dependence of optical readout/servo signals,” Jpn. J. Appl. Phys. 32, 3175–3184 (1993).
[CrossRef]

Li, L.

Marchant, A. B.

H. Engstrom, A. B. Marchant, “Polarization considerations in magneto-optical recording,” in Polarization Considerations for Optical Systems II, R. A. Chipman, ed., Proc. SPIE1166, 69–78 (1989).
[CrossRef]

Ooki, H.

H. Ooki, “Vector diffraction theory for magneto-optical disc systems,” Optik 89, 15–22 (1991).

Pasman, J.

J. Pasman, “Vector theory of diffraction,” in Principles of Optical Disc Systems, G. Bouwhuis, ed. (Hilger, Bristol, UK, 1985).

Sheng, P.

P. Sheng, “Theoretical considerations of optical diffraction from RCA VideoDisc signals,” RCA Rev. 39, 513–555 (1978).

Appl. Opt. (1)

J. Opt. Soc. Am. (1)

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

Jpn. J. Appl. Phys. (1)

K. Kobayashi, “Vector diffraction modeling: polarization dependence of optical readout/servo signals,” Jpn. J. Appl. Phys. 32, 3175–3184 (1993).
[CrossRef]

Optik (1)

H. Ooki, “Vector diffraction theory for magneto-optical disc systems,” Optik 89, 15–22 (1991).

RCA Rev. (1)

P. Sheng, “Theoretical considerations of optical diffraction from RCA VideoDisc signals,” RCA Rev. 39, 513–555 (1978).

Other (3)

DELTA is a diffraction grating program written by Lifeng Li; DIFFRACT is a product of MM Research, Inc., Tucson, Arizona. The theoretical basis of DIFFRACT has been described in the following papers by M. Mansuripur: “Certain computational aspects of vector diffraction problems,” J. Opt. Soc. Am. A 6, 789–805 (1989); “Distribution of light at and near the focus of high-numerical-aperture objectives,” J. Opt. Soc. Am. A3, 2086–2093 (1986); erratum, 382–383 (1993); “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).

H. Engstrom, A. B. Marchant, “Polarization considerations in magneto-optical recording,” in Polarization Considerations for Optical Systems II, R. A. Chipman, ed., Proc. SPIE1166, 69–78 (1989).
[CrossRef]

J. Pasman, “Vector theory of diffraction,” in Principles of Optical Disc Systems, G. Bouwhuis, ed. (Hilger, Bristol, UK, 1985).

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Figures (18)

Fig. 1
Fig. 1

Diagram of the basic readout system; the differential detector module consisting of a Wollaston prism and two identical photodetectors can rotate around the optical axis for the purpose of alignment and balancing of the two detectors.

Fig. 2
Fig. 2

Structural and optical parameters of the quadrilayer MO stack used in our simulations. The substrate is polycarbonate with a refractive index n = 1.58. The dielectric layers are SiN with a refractive index of 2.2. The reflector layer is AlCr with a complex refractive index (n, k) = (1.9, 6.2). The diagonal and off-diagonal elements of the dielectric tensor of the MO layer (an amorphous TbFeCo ferrimagnetic alloy) are ∊ = -8.03 + i28 and ∊′ = 0.63 - i0.18. The arrows within the MO layer indicate the direction of magnetization in the recorded stripes.

Fig. 3
Fig. 3

Computed differential signals obtained when a one-dimensional periodic array of magnetic domains is scanned. In this simulation, λ = 0.633 µm and the NA is 0.8, leading to a resolution limit of 0.40 µm for the readout system. (a)–(c) Signals for the cases of p = 1.6, 0.8, and 0.5 µm, respectively. In (a) the signals for E (vector and scalar) overlap. In (b) the vector signals for E and E are nearly the same.

Fig. 4
Fig. 4

Same as Fig. 3 but for the case of a NA of 0.6. (a)–(c) Signals for the cases of p = 2.4, 1.0, and 0.6 µm, respectively.

Fig. 5
Fig. 5

Same as Fig. 3 but for the case of a NA of 0.4. (a)–(c) Signals for the cases of p = 3.2, 1.4, and 0.9 µm, respectively. Only the results of vector calculation are shown here.

Fig. 6
Fig. 6

Images of parallel magnetic lines obtained through a polarized-light microscope. (a) Line recorded at λ = 0.680 µm and a NA of 1.2; (b) lines recorded at λ = 0.780 µm and a NA of 0.8.

Fig. 7
Fig. 7

Experimental setup. The light from a red He–Ne laser is focused onto the sample by the objective lens. The reflected light from the sample is directed to the Wollaston prism and then to the split detectors through the beam splitter BS2 and the lens L3. The other part of this setup, which uses white light from a fiber bundle, is needed for alignment purposes. The sample is placed on the translation and rotation stage. To measure the MO signal, the polarizer P1 is set such that the incident polarization is parallel to the magnetic lines; the sample is rotated when we want to measure the read signal for E . To measure the reflected signal from a PC medium, the optical axis of the polarizer P1 is set at approximately 45° relative to the parallel crystalline lines on the sample so that the E and E signals can be measured simultaneously.

Fig. 8
Fig. 8

Experimental data from the MO sample obtained when p ≈ 1.35 µm and the NA equals 0.6. (a) and (b) are the scanned images of the magnetic lines with E and E beams, respectively. (c) and (d) are the averaged differential MO signals along the horizontal direction.

Fig. 9
Fig. 9

Same as Fig. 8 except p ≈ 0.93 µm.

Fig. 10
Fig. 10

Same as Fig. 8 except p ≈ 0.72 µm.

Fig. 11
Fig. 11

Computed and measured differences between the E and the E signals [defined as (signal for E - signal for E )/(signal for E + signal for E )] versus the period of the magnetic line domains obtained with a NA of 0.6. (a) simulation and (b) experiment.

Fig. 12
Fig. 12

Experimental data from the MO sample obtained when the NA equals 0.4. Shown are the averaged differential MO signals along the horizontal direction for (a) and (b) p ≈ 1.75 µm, (c) and (d) p ≈ 1.42 µm, and (e) and (f) p ≈ 1.0 µm.

Fig. 13
Fig. 13

(a) Readout system used in the simulations of the PC medium. (b) Front surface quadrilayer PC stack used in the simulations. The substrate is polycarbonate with a refractive index n = 1.58. The dielectric layers are ZnS-SiO2 mixtures with a refractive index of 2.1. The reflector layer is AlCr with a complex refractive index (n, k) = (1.8, 6.0). The PC film (GeSbTe) has complex indices (4.2, 1.9) in the amorphous state and (4.6, 4.2) in the crystalline state.

Fig. 14
Fig. 14

Computed readout signals by use of vector diffraction theory obtained when parallel crystalline lines are scanned on a PC sample. In this simulation λ = 0.633 µm and the NA equals 0.6, leading to the resolution limit of p cutoff = 0.53 µm. (a)–(c) Computed signals for the cases of p = 2.0, 1.0, and 0.6 µm, respectively.

Fig. 15
Fig. 15

Photograph of parallel crystalline lines on an amorphous sample obtained through a microscope.

Fig. 16
Fig. 16

Experimental results obtained from a PC sample on which parallel crystalline lines were recorded with p ≈ 1.2 µm and a NA of 0.6. (a) and (b) are scanned images with E and E beams, respectively. (c) The averaged reflected signals along the horizontal direction.

Fig. 17
Fig. 17

Same as Fig. 16 except p ≈ 0.8 µm.

Fig. 18
Fig. 18

Same as Fig. 16 except p ≈ 0.7 µm.

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