Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-03-15
2001-10-16
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044120, C369S112010, C369S126000
Reexamination Certificate
active
06304527
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a near-field optical head, a manufacturing method of the near-field optical head, and an optical recording/readout system using the near-field optical head.
Recently, an optical recording using near-field light has received attention as a method for making an optical disc device extremely dense. For example, the following experimental results were reported in Applied Physics Letters, Vol. 61, No. 2, pp. 142-144, 1992: a probe was made by shaving the top of an optical fiber into a cone and by coating it with metal except for several tens nm of the top and was mounted on a precision actuator using a piezo device, and a recording mark of 60 nm in diameter was recorded or read out on or from a platinum/cobalt multi-layer by controlling the position of the probe. In this case, a shear-force method applying an atomic force to the control of a gap between the probe is used and a recording medium and an areal density reached 45 gigabit/in
2
, which is about 20 times the present areal density. Further, in Japanese Unexamined Patent Publication No. 3-171434, a method is disclosed wherein near-field light is excited by focusing light on a small pinhole by a lens and a gap between the small pinhole and a recording medium is controlled with the use of an atomic force generated between a cantilever having the small pinhole at the top thereof and the recording medium, and another method is disclosed wherein a slider which receives a light source, a lens and a small pinhole is arranged on a medium and is flown by air to control a gap between the small pinhole and the recording medium.
SUMMARY OF THE INVENTION
In an optical information-recording/readout system, in order to increase an information transfer rate, it is necessary to increase a relative speed of a recording medium to an optical head for recording/reading-out information.
However, in the above-mentioned first conventional example using the shear-force method applying the atomic force to the control of the gap between the probe and the recording medium, the gap between the recording medium and the optical head, that is, the fiber probe is required to be controlled with a scanning force microscopy with extremely high accuracy and hence there exists a problem in that if an information-recording disc is rotated at high speeds, the gap between a substrate having a high frequency produced by a radial positioning error of the disc and that the probe can not be controlled with high accuracy and therefore an information data transfer rate can not be increased.
Further, in the conventional example using the cantilever, a change in capacitance or a laser interferometric measurement is used as a method for detecting a displacement of the cantilever and hence there exists a problem in that a large-scale optical system or a capacitance measurement system other than an illumination optical system for exciting near-field light is required and that the system is made larger and more complex. Furthermore, the following optical lever method was reported in Applied Physics Letters, Vol. 68, No. 25, pp. 3531-3533, 1996: the displacement of a cantilever was converted into the movement of a light point on a linear photodiode by irradiating the cantilever with laser light at the back thereof to detect the displacement of the cantilever. However, also in this case, there exits a problem in that a large-scale optical system other than an illumination optical system for exciting near-field light is required and that the system is made larger and more complex.
Furthermore, in the conventional example having the slider which receives the light source, the lens and the small pinhole on the medium, many optical parts such as light source, lens and the like are mounted on the slider and hence the mass of the slider is increased to deteriorate the following of an up-down oscillation caused by the rotation of the recording medium by the slider, which makes it impossible to constitute the system. Still further, in Japanese Unexamined Patent Publication No. 3-171434, a method for mounting and forming the pinhole, the laser light, and the lens is not disclosed in the concrete.
An object of the present invention is to provide a near-field optical head capable of increasing a relative speed of a recording medium to the optical head for recording/reading-out information so as to increase an information data transfer rate of an ultra-high density optical recording/readout system using a probe for exciting near-field light. Further, another object of the present invention is provide a near-field optical head which does not need an additional unit for detecting a gap between the recording medium and the optical head and hence is reduced in size and weight and constituted simply. Furthermore, still another object of the present invention is to provide an optical recording/readout system using this kind of near-field optical head.
To solve the above-mentioned problems, the present invention adopts the following means.
A cylindrical or prismatical pad for controlling the state of contact or flying of an optically transparent slider with or to an information-recording medium and a probe for exciting near-field light having a small spot size are mounted on the surface of the slider opposite to the information-recording medium such that the pad is near to the probe, wherein the slider moves relatively to the information-recording medium while keeping contact with or a nearly constant gap to the information-recording medium, and further the height of the probe is nearly equal to and smaller than the height of the pad from the surface of the slider opposite to the information-recording medium. Accordingly, the near-field optical head is integrally formed with the slider to constitute a near-field optical head which is reduced in size and weight and is simply constituted and has the same performance as a head used in a conventional hard disc drive. Further, since the slider is reduced in size and weight, it is possible to increase a relative speed of the recording medium to the optical head for recording/reading-out information.
Further, in the near-field optical head described above, the near-field optical head having a small spot size can be excited by forming an optically opaque film, for example a metallic film, on the pad and the probe, and further by making at the top the probe a small aperture in which the constituent of the probe is exposed and the surface of the exposed constituent of the probe and in which the surface of the metallic thin film are substantially on the same plane.
Still further, in the near-field optical head described above, the probe can be shaped into an arbitrary pyramidal structure or the small aperture can be made in the top of the probe by arranging the pad in such a way to surround the probe and by dividing the pad into at least a plurality of parts and by arranging the divided parts in such a way that the probe can be seen through a gap between the divided parts when viewed from the side of the pad and by etching the probe by irradiating the probe with a particle beam from the side of the probe. Furthermore, an optical recording readout system of ultra-high density can be constituted with the use of the near-field optical head, a light source for supplying illumination light to the near-field optical head, an optical recording medium, a detection system for detecting a modulated signal of the near-field light excited by the near-field optical head by the recording medium.
REFERENCES:
patent: 5946284 (1999-08-01), Chung et al.
patent: 5959957 (1999-09-01), Ikeda et al.
patent: 5986995 (1999-11-01), He et al.
patent: 3-171434 (1991-07-01), None
Applied Physics Letters, vol. 61, No. 2, Jul. 13, 1992, “Near-field magneto-optics and high density data storage”, E. Betzig et al, pp. 142-144.
Applied Physics Letters, vol. 68, No. 25, Jun. 17, 1996, “Multipurpose sensor tips for scanning near-field microscopy”, C. Mihalcea et al, pp. 3531-3533.
Applied Physics Letters, vol. 68, No. 19, May 6, 1
Hosaka Sumio
Ito Kenchi
Muranishi Masaru
Nakamura Kimio
Edun Muhammad
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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