Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
1999-06-23
2001-02-06
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C359S364000, C359S719000, C359S727000, C369S013010, C369S014000, C369S112040
Reexamination Certificate
active
06185051
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to optical focusing devices, and it particularly relates to a high numerical aperture (NA) optical focusing device. More particularly, the present invention relates to an optical focusing device comprising a parabolic reflective surface or a combination of optical surfaces, for generating an evanescent optical field that enables its 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 electro-magnetic 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 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 cannot be greater than 1 if the focusing spot is located in free space, 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 data storage system that uses an optical focusing device for focusing an incident optical beam to a small size focal spot.
According to one embodiment of the present invention, the optical focusing device includes an optically transmissive body which is defined by a generally flat incident surface, a flat, bottom surface disposed opposite and parallel to the incident surface, and a reflective side coated with a reflective layer for reflecting the optical beam through the body toward the bottom surface. The bottom surface defines a focal plane on which the focal spot is formed, for generating a localized evanescent field.
The focal spot is located along a central axis P, in very close proximity to the data storage disk, such that the localized evanescent field interacts with a recording medium of the disk, for enabling data to be transduced to and from the disk by effecting near field coupling. An electromagnetic coil or coil assembly, can optionally be formed on the bottom surface, co-axially with the focal spot, for generating a desired write magnetic field.
The reflective side of the optical focusing device preferably has a parabola shaped curvature, but other shapes can alternatively be selected. For example, the side curvature can have a tilted parabola shape.
According to another embodiment, the optical focusing device further includes an optically transmissive, complementary conical element with a generally flat incident surface and a conical exit surface. The complementary conical element is also comprised of a cylindrical side having a circular cross-section.
According to still another embodiment, the focusing device further includes a second complementary conical element which is disposed intermediate the body of the main focusing element and the complementary conical element. The second complementary conical element is optically transmissive and includes an incident conical surface, and a flat exit surface, such that the conical exit surface of the complementary conical element and the incident conical surface of the second complementary conical element can be fitted together to form a cylindrical axicon
According to yet another embodiment, the focusing device includes a conical element and a complementary element having an optically transmissive body. The body is defined by a conically shaped incident surface, a flat bottom surface disposed opposite to the incident surface, a cylindrical side with a circular cross-section, a reflective side coated with a reflective layer for reflecting the optical beam through the body toward the bottom surface, such that the bottom surface defines a focal plane on which the focal spot is formed, for generating an evanescent field.
According to another embodiment, the focusing device includes an optically transmissive body defined by an incident conical surface, a generally flat bottom surface disposed opposite to the incident surface, a reflective side for reflecting the optical beam through the body toward the bottom surface. In a variation to this embodiment, the focusing device further includes a cylindrical side with a circular cross-section.
Another aspect of the present invention is the ability to mass-produce the optical devices at wafer level. The manufacturing method includes forming a plurality of substantially identical lens plates on an optical wafer wherein each lens plate contains at least one focusing device. The lens plates are formed by etching a plurality of openings in the optical wafer, such that each opening extends through the entire height of the optical wafer and corresponds to one optical device. Each opening is contoured by a wall having the shape of the reflective side. The openings are then filled with an optical material, and the top and bottom surfaces of the optical wafer are then lapped to a desired height. The individual lens plates are sliced along cutting lines.
REFERENCES:
patent: 3999855 (1976-12-01), Hirschfeld
patent: 5042928 (1991-08-01), Richards
patent: 5125750 (1992-06-01), Corle et al.
patent: 5285318 (1994-02-01), Gleckman
patent: 5497359 (1996-03-01), Mamin et al.
patent: 5689480 (1997-11-01), Kino
patent: 5986995 (1999-11-01), He et al.
patent: 758753 (1996-02-01), None
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 Processin
Chen Hong
Cheng Charles C. K.
He Chuan
Miceli, Jr. Joseph J.
Epps Georgia
Kassatly Samuel A.
Read-Rite Corporation
Spector David N.
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