Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-03-05
2001-09-18
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044140, C369S112230
Reexamination Certificate
active
06292442
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical head apparatus for optical discs, and particularly to an optical head used for producing master optical discs.
In order to increase recording density of an optical disc, laser light having a short wavelength and/or an object lens with a large numerical aperture must be used.
However, it is not easy to develop a semiconductor laser which emits laser light having a short wavelength. While enlarging the diameter of the object lens broadens the numerical aperture of the object lens, the optical head itself consequently becomes large in size.
Hence, recording information on an optical disc using a Solid Immersion Lens (referred to as SIL, hereinafter) is proposed by Mr. S. M. Mansfield et. al. in “High-numerical-aperture lens system for optical storage” (OPTICS LETTERS/Vol. 18, No. 4 305-307/Feb. 15, 1993).
This is a method wherein laser light gathered by the object lens is radiated on the SIL, which further converges the laser light. A minute spot can be formed by using the SIL.
In order to form a minute spot by the SIL, it is necessary to converge the laser light onto the bottom surface of the SIL. Therefore, the laser light must be led into the SIL after having been sufficiently gathered by the object lens. In other words, the object lens must be controlled so that it can be always optimally positioned relative to the SIL.
In order to perform the above-mentioned control, it is necessary to generate a focus error signal according to the reflected light from the SIL. However, the reflected light detected by a detector includes those reflected from the spherical surface of the SIL, the bottom surface of the SIL, and the master optical disc or the like.
Hence, the output derived from the light received by the detector includes much noise and is not acceptable to be used directly as the focus error signal for controlling the object lens to be optimally positioned.
SUMMARY OF THE INVENTION
Considering the above-mentioned problems, it is an object of the present invention to provide an optical head using an SIL.
To be concrete, it is an object of the preset invention to provide an optical head which can adjust the distance between the object lens and the SIL to be constant, which stabilizes formation of the minute spot.
It is another object of the present invention to provide an optical head which can effectively select a specified reflected light from the SIL to be detected, for adjusting the distance between the object lens and the SIL to be constant.
To attain the above object, the present invention provides an optical head comprising an object lens for converging light which is radiated on a recording surface of a recording media, a solid immersion lens for further converging the light which has been converged by the object lens, drive means for driving the object lens along an optical axis thereof, and control means for controlling the drive means so that the distance between the object lens and the solid immersion lens along the optical axis is kept constant, according to reflected light from the solid immersion lens.
Furthermore, the present invention provides an optical head as composed above, in which further the solid immersion lens is mounted on a floating slider, and the distance between the recording media and the solid immersion lens is kept constant.
The present invention still further provides an optical head as composed above, further comprising means for separating and receiving the reflected light from the spherical surface of the solid immersion lens, and in which the control means controls the drive means according to the output derived from the light received by the means for separating and receiving the reflected light.
In addition, the present invention provides an optical head as composed above, further comprising a reflective membrane or a reflective layer disposed on the surface of the solid immersion lens for reflecting the light which has been converged by the object lens.
REFERENCES:
patent: 5764613 (1998-06-01), Yamamoto et al.
patent: 6005834 (1999-12-01), Maeda et al.
patent: 6055222 (2000-04-01), Knight
patent: 6061322 (2000-05-01), Jain et al.
Arent Fox Kintner & Plotkin & Kahn, PLLC
Edun Muhammad
Pioneer Electronic Corporation
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