Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-01-21
2001-04-03
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112140
Reexamination Certificate
active
06212153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to optical devices, and it particularly relates to a high numerical aperture (NA) catadioptric focusing device having a flat kinoform phase profile, for use in data storage systems such as optical and magneto-optical (MO) disk drives.
2. Description of Related Art
In a MO storage system, a thin film read/write head includes an optical assembly for directing and focusing an optical beam, such as a laser beam, and an electromagnetic coil that generates a magnetic field for defining the magnetic domains in a spinning data storage medium or disk. The head is secured to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of the disk. In operation, a lift force is generated by the aerodynamic interaction between the head and the disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the disk.
A significant concern with the design of the MO head is to increase the recording or areal density of the disk. One attempt to achieve objective has been to reduce the spot size of the light beam on the disk. The diameter of the spot size is generally inversely proportional to the numerical aperture (NA) of an objective lens forming part of the optical assembly, and proportional to the wavelength of the optical beam. As a result, the objective lens is selected to have a large NA. However, the NA in objective lenses can be 1 if the focusing spot were in air, thus limiting the spot size. Another attempt to reduce the spot size and to increase the recording areal density has been to use solid immersion lenses (SILs) with near field recording, as exemplified by the following references:
U.S. Pat. No. 5,125,750, titled “Optical Recording System Employing a Solid Immersion Lens”.
U.S. Pat. No. 5,497,359, titled “Optical Disk Data Storage System With Radiation-Transparent Air-Bearing Slider”.
Yet another attempt at improving the recording head performance proposes the use of near-field optics, as illustrated by the following reference:
U.S. Pat. No. 5,689,480, titled “Magneto-Optic Recording System Employing Near Field Optics”.
A catadioptric SIL system is described in the following references, and employs the SIL concept as part of the near-field optics:
Lee, C. W., et al., “Feasibility Study on Near Field Optical Memory Using A Catadioptric Optical System”, Optical Data Storage, Technical Digest Series, Volume 8, pages 137-139, May 10-13, 1998; and
“Parallel Processing”, 42 Optics and Photonics News, pages 42-45, June 1998.
While this catadioptric SIL system can present certain advantages over conventional SILs, it does not appear to capture the entire incident, collimated beam. This represents a waste of valuable energy that could otherwise increase the evanescent optical field.
Other concerns related to the manufacture of MO heads are the extreme difficulty and high costs associated with the mass production of these heads, particularly where optical and electromagnetic components are assembled to a slider body, and aligned for optimal performance.
SUMMARY OF THE INVENTION
One aspect of the present invention is to satisfy the long felt, and still unsatisfied need for a near-field optical or MO disk data storage system that uses a catadioptric focusing device or lens with a high numerical aperture (NA), which does not introduce significant spot aberration on the disk.
Another aspect of the present invention is to provide a focusing device that has generally flat surfaces that act as reference surfaces and facilitate its manufacture and its assembly to the head.
The focusing device includes an incident surface, a bottom reflective surface, a focal pedestal, and a body. The incident surface is generally flat and is comprised of a central diffractive, optically transmissive facet or surface and a peripheral facet or surface comprised of a kinoform phase profile. In a data writing or reading mode, the incident optical beam, such as a laser beam impinges upon the central facet, and is diffracted thereby. The incident laser beam can be collimated, convergent or divergent.
The laser beam passes through the transparent body, and impinges upon the bottom reflective surface. The laser beam is then reflected by the bottom reflective surface, through the body, unto the kinoform phase profile. The laser beam is reflected and refracted by the peripheral kinoform phase profile as a focused beam, through the body, and is focused as a focal point. The focal point is preferably located at, or in close proximity to a pedestal edge, along a central axis, in very close proximity to the disk. This will allow the focused optical beam to propagate toward, or penetrate the disk through evanescent wave coupling, for enabling the transduction of data to and from the disk.
REFERENCES:
patent: 4835380 (1989-05-01), Opheij et al.
patent: 4940890 (1990-07-01), Opheij et al.
patent: 5029255 (1991-07-01), Opheij et al.
patent: 5042928 (1991-08-01), Richards
patent: 5125750 (1992-06-01), Corle et al.
patent: 5497359 (1996-03-01), Mamin et al.
patent: 5689480 (1997-11-01), Kino
patent: 5986995 (1999-11-01), He et al.
Lee, C.W., et al., “Feasibility Study on Near Field Optical Memory Using A Catadioptric Optical System”, Optical Data Storage, Technical Digest Series, vol. 8, pp. 137-139, May 10-13, 1998.*
Mansipur, M. et al. “Parallel Processing”, 42 Optics and Photonics News, pp. 42-45, Jun. 1998.
Chen Hong
Cheng Charles C.
He Chuan
Stovall Ross W.
Hayden Robert
Kassatly Samuel A.
Read-Rite Corporation
Tran Thang V.
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