Radiant energy – Ionic separation or analysis – Static field-type ion path-bending selecting means
Patent
1989-10-18
1991-02-12
Healy, Brian
Radiant energy
Ionic separation or analysis
Static field-type ion path-bending selecting means
350 9611, 350 9612, 3501622, 35016221, 35016223, 2502015, 369 4412, 369 4414, G02B 634, G02B 2742, G11B 700
Patent
active
049919199
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an optical head apparatus which records or reads information onto or out of optical disks.
BACKGROUND ART
Technologies by which optical head apparatuses that record or read information onto or out of optical disks are made into thin films have been proposed by, for example, the 46th academic lecture meeting 2p-L-15 of the Applied Physics Association of Japan. FIG. 1 shows the construction of this conventional thin film optical head apparatus.
In FIG. 1, the reference numeral 133 is a semiconductor laser, 132 is a waveguiding layer, 135 is a grating beam splitter (GBS), 136 is a focusing grating coupler (FGC), 11 is an optical disk, 140A, 140B and 141A, 141B are light detectors. The waveguiding layer 132 is formed over a substrate 131 to sandwich a dielectric layer with a low refractive index therebetween. Laser light emitted by the semiconductor laser 133 spreads while passing through the waveguiding layer 132 to become waveguided light 134 in a TE mode. The waveguided light 134 is converted to parallel light rays by the GBS 135 which is formed on the waveguiding layer 132, and a part of the parallel light becomes radiation mode light 137. The radiation mode light 137 is focused onto a focal point FC and is reflected by the reflecting surface of the optical disk 11 located at the focal point FC to return to the FGC 136 where it is converted to waveguided light again. The waveguided light is split by the GBS 135 into waveguided lights 138 and 139, which are then focused onto the light detectors 140A, 140B and 141A, 141B.
The reflecting surface of the optical disk 11 is provided with guide grooves running along the rotation direction 12 of the disk and arranged periodically in a radial direction, to thereby diffract the reflected light in the radial direction of the disk. Because the interference of the diffracted light causes tracking error (TE) appearing as an unevenness in the amount of the reflected light 137 in the radial direction of the disk, a TE signal can be obtained by measuring the amounts of waveguided lights 138 and 139 and taking the difference therebetween (so-called push-pull detection). By splitting the waveguided light by means of the GBS 135, the defocus of the optical disk reflecting surface is represented by the difference in the light amount distribution on the light detectors 140A and 140B or 141A and 141B, based on the same principle as the focus error (FE) detector by means of a knife edge. Consequently the TE signal is obtained by taking the difference between the summation signal of light detectors 140A and 140B and the summation signal of 141A and 141B by a differential amplifier 144, and the FE signal is obtained by taking the difference between the summation signal of light detectors 140A and 141A and the summation signal of 140B and 141B by a differential amplifier 143. On the other hand, the summation signal of the light detectors 140A, 140B, 141A and 141B is obtained by means of a summing amplifier 142 and is used as a reproduced signal.
However, optical head apparatuses of such a construction as described above have the following problems.
First, a semiconductor laser causes fluctuation in the wavelength depending on the temperature and the magnitude of the output power, so that the diffraction angle of light by the GBS 135 changes, causing the waveguided light 134 to be incident on the FGC 136 in a state that deviates from parallel light. Therefore, aberration (astigmatism in particular) is generated in the radiation light 137 due to unparallelism and the difference in the optical path. Also, because the diffraction angle of the radiation light 137 from the FGC 136 changes, the angle of incidence onto the optical disk 11 changes, and coma arises by the action of a transparent substrate which covers the reflecting surface of the optical disk. These aberrations cause the focusing characteristics of the light distribution on the reflecting surface to deteriorate and the reproduction performance (or recording performance) to decrea
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Mizuno Sadao
Nishiwaki Seiji
Taketomi Yoshinao
Tomita Takaaki
Uchida Shinji
Healy Brian
Matsushita Electric - Industrial Co., Ltd.
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