Optical: systems and elements – Lens
Reexamination Certificate
2002-06-03
2004-04-06
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
C359S796000, C264S001100, C065S047000
Reexamination Certificate
active
06717738
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical element, a mold of producing the optical element, and a method of producing the optical element.
BACKGROUND ART
As the conventional methods for producing a conventional optical element, there is known, for example, a method for producing an optical element wherein molten glass or another optical material is filled into a mold having a cavity formed to the desired lens shape to produce a molded lens.
Also, there is known a method for producing an optical element wherein reactive ion etching (RIE) or another etching method is applied to etch an optical material to a desired lens shape by using a photoresist as an etching mask.
Further, there is known a method for producing an optical element wherein an optical material is mechanically polished to form a desired lens shape.
In a data storage apparatus such as a magneto-optic disk apparatus or DVD (digital versatile disk) apparatus an optical head is arranged close to the surface of a disk-like data recording medium and a converged laser beam is exposed onto a data recording media surface to record data on data recording medium or read data from the data recording medium.
When trying to raise a recording density of data in order to achieve a larger capacity of data recording in such a data storage apparatus, the laser beam must be sharply converged and exposed on the surface of the data recording medium, and it is necessary to use an object lens having a high numerical aperture (NA). In this case, if a large sized lens is used, the optical head ends up becoming large, then, a diameter of the lens must be kept at a small size. Accordingly, this means usage of a lens having a high numerical aperture and having a small size. As a result, it becomes necessary to arrange the lens extremely close to the surface of the data recording medium.
A floating type optical head operates in a state forming a thin air gap with the surface of the high speed rotating data recording medium and slightly floating from the surface of the data recording medium, so enables the lens to be arranged close to the surface of the data recording medium and, accordingly, is advantageous for achieving a higher density of recorded information. The floating type optical head can be constituted by the above optical element.
FIGS. 19A
to
19
E are views of production processes for producing an optical element applied to a conventional floating type optical head and show side sectional views of the optical element at different stages of the production process. Referring to these drawings, a method for producing a conventional optical element will first be explained. In this example, an object lens having a high numerical aperture obtained by combining an ordinary lens
2112
and a ball lens
2106
is used to form an optical element.
As shown in
FIG. 19A
, at the center of a flat slider substrate
2102
rectangular when seen from a plan view, first, a lens holding hole
2104
conical in shape and passing through the slider substrate
2102
is formed. As shown in
FIG. 19B
, a spherical ball lens
2106
is dropped into this hole
2104
and fixed by bonding, then a portion
2106
A of the ball lens
2106
projecting from the lens holding hole
2104
is polished to the same level as the bottom surface of the slider substrate
2102
as shown in FIG.
19
C. The bottom surface of the slider substrate
2102
flattened in this way and the bottom surface of the ball lens
2106
become surfaces slightly floating from the surface of the data recording medium.
Next, as shown in
FIG. 19D
, in order to form two floating use rails
2108
and
2108
at the two end portions of the bottom surface of the slider substrate
2102
, two grooves
2110
and
2110
sandwiching the ball lens
2106
is formed by for example dry etching such as ion milling or RIE (reactive ion etching) and selective etching utilizing semiconductor photolithography.
Finally, a lens
2112
(for example, a molded glass lens) formed by another process is arranged and fixed by bonding on the slider substrate
2102
so as to close the opening of the lens holding hole
2104
, whereby an optical element
2114
is completed.
In the above conventional method for producing an optical element, for example, the method for producing a molded lens, the formation of the cavity is troublesome in work.
In the above conventional method for producing an optical element, for example, the method for producing an optical element using RIE or another etching technique, the use of the optical material is restricted. There are few optical materials having a high refractive index giving a lens having a large numerical aperture NA among optical materials capable of RIE or other etching.
Also, a method of production for producing a plurality of optical systems is demanded from the viewpoint of reducing the production costs of optical systems.
Further, when forming a floating type optical head by using the above optical element, in order to record data on the data recording medium at a high density and reproduce data recorded at a high density from the data recording medium, it is necessary to sharply converge the laser beam and expose the converged beam on a specific position on the data recording medium with a good precision. Accordingly, when forming the conventional floating type optical head
2114
, an extremely high precision is required particularly in the work for formation and assembly of the lens, the work took a long time, skill was necessary. Also, it was necessary to form the parts used with a very high precision too.
For example, the lens holding hole
2104
must be formed in the slider substrate
2102
with a high precision, and the ball lens
2106
must be arranged and fixed in the lens holding hole
2104
with a high precision. Also, in order to form the ball lens
2106
an extremely high sphericity and precision of radius are required. Further, in the polishing of the ball lens
2106
projecting from the lens holding hole
2104
, it is necessary to control the amount of polishing with a high precision so that the polished level becomes the same as the surface of the slider substrate
2102
. Further, when arranging the lens
2112
on the lens holding hole
2104
as well, the lens must be positioned with an extremely high precision of the &mgr;m order three-dimensionally. This positioning has been conventionally carried out by observing aberration etc, and the lens
2112
has a shape as a double convex lens so is hard to handle. As a result, the work takes a long time and skill becomes necessary.
As discussed above, high precision parts are necessary and the work efficiency is poor, therefore, in the end, the cost becomes high. Further, since the lens
2112
is arranged on the lens holding hole
2104
and the lens
2112
projects from the slider plate
2102
, such the condition is disadvantageous from the point of reduction of the size.
Accordingly, an optical element which can be easily produced and which is advantageous in realizing a floating type optical head with an inexpensive production cost, a production use mold useable for the production of the optical element, and a method for producing the optical element have been sought.
The present invention was made in order to overcome the above disadvantages.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to provide an optical element which can be easily produced and is inexpensive in production cost, a production use mold useable for the production of the optical element, and a method for producing the optical element.
According to the present invention, the following optical element is provided: This optical element is an optical element having a substrate made of an optical material, the optical element characterized in that one surface of the substrate is formed with a convex portion having a first curvature, another surface facing the convex portion of the one surface of the substrate is formed with a concave portion having a second curvature, and the concave portion is filled wi
Watanabe Tetsu
Yamada Masahiro
Choi William
Epps Georgia
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
LandOfFree
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