1995 Fiscal Year Final Research Report Summary
Signal Detection of Magneto-Optical Disk with Defocused Beam
| Project/Area Number |
06650390
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
電子デバイス・機器工学
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| Research Institution | Wakayama University |
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Principal Investigator |
NUMATA Takuhisa Wakayama University, Faculty of Systems Engineering, Professor, システム工学部, 教授 (80135673)
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| Co-Investigator(Kenkyū-buntansha) |
OKAMURA Yasuyuki Osaka University, Faculty of Engineering Science, Associate Proffesor, 基礎工学部, 助教授 (80144442)
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| Project Period (FY) |
1994 – 1995
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| Keywords | High Density Optical Recording / Optical Disk / Magneto-Optical Disk / Optical Fourier Transform / Magneto-Optical Head |
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| Research Abstract |
A readout method of high density magneto-optical disk was proposed. In this method, the recorded medium is not placed at the beam waist of the converging beam in the optical system like the conventional method but slightly off positioned from the waist. A circularly polarized beam is employed and the distribution of phase retardation in the illuminated area is discriminated with far-field diffraction pattern.
A theoretical calculation was established to estimate the far-field pattern of magneto-optical record, and was confirmed experimentally utilizing a magnetic garnet film with a large magneto-optical effect.
The performance of the defocused method depends on the amount of the defocusing and on the relative dimensions of the reversed domain with respect to that of the beam waist. The readout signal was calculated on the widely used magneto-optical disk material with several parameters of the optical system varied.
In reading a small isolated reversed domain, the readout signal decays with decrease of the domain diameter slowly than the conventional readout method, hence, the defocused method has an advantage of giving larger readout signal than the conventional method in this case. Depending on the diameter of the reversed domain, there exists a preferable amount of defocusing of several microns.
Since this method utilized the light diffraction at domains, the far-field pattern, i.e.the readout signal, grows and increases for the regular domain patterns. For a random domain pattern the readout signal deteriorates rapidly, and the estimation of this defocused method should be done under some code modulations.
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