Optical: systems and elements – Lens – With reflecting element
Reexamination Certificate
2001-08-01
2004-12-21
Yoon, Tae H. (Department: 1714)
Optical: systems and elements
Lens
With reflecting element
C359S653000, C359S708000, C359S720000, C524S492000, C524S493000, C524S588000
Reexamination Certificate
active
06833965
ABSTRACT:
This application claims benefit of Japanese Application No. 2000-234056 filed in Japan on Aug. 2, 2000, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical element using an organic-inorganic composite material. More particularly, the present invention relates to an optical element using organic-inorganic composite material which is suitable for use in optical systems such as an image pickup system and an ocular system.
2. Discussion of Related Art
Conventional transparent optical elements are produced by using a glass material (inorganic material) or a plastic material (organic material). When a glass material is used to produce an optical element, polishing is generally performed to form the material into the desired shape. Therefore, a great deal of time is required to carry out the polishing process. In the case of a plastic material, on the other hand, an optical element can be produced by injection molding. Accordingly, optical elements formed from a plastic material are superior in productivity but inferior in temperature characteristics. In addition, the number of kinds of plastic materials usable to produce optical elements is unfavorably small. In particular, there is no plastic material exhibiting a high refractive index.
There has recently been known a method of producing an optical element from a glass material by molding. With this method, however, the kinds of glass materials usable for production by molding are limited. Usable glass materials are restricted within a very narrow range. There is also a method wherein an optical element is molded from a thermosetting resin material as a plastic material. This method also has the disadvantage that usable thermosetting resin materials are limited. In particular, there is no thermosetting resin material having a high refractive index and exhibiting minimal dispersion.
Let us put the above-described problems in order.
Problems of glass materials:
1. Heavy in specific gravity.
2. Inferior in productivity.
Problems of plastic materials:
1. There is no plastic material having a high refractive index and exhibiting minimal dispersion.
2. Plastic materials are hygroscopic.
3. Exhibiting birefringence.
4. Weak in mechanical strength
Conventional optical elements using a glass material are heavy in specific gravity. Therefore, an increase in weight gives rise to a problem, particularly in the case of an optical element having a large lens aperture, e.g. an ocular lens. Weight is a matter of great concern for an optical element having a large aperture, e.g. a telephotographic lens for use with a camera. In addition, because lenses using a glass material are produced by polishing, much time is required for the polishing process.
Regarding plastic materials, there is no plastic material having a high refractive index, in particular. High-refractive index materials used for eyeglasses exhibit large dispersion and hence cause large chromatic aberrations. Because they are thermosetting plastic materials, a great deal of time is required for setting. Further, because plastic materials are hygroscopic, optical elements molded therefrom absorb water contained in the air even under normal environmental conditions, causing a change in shape and also a change in refractive index.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-described problems with the prior art.
An object of the present invention is to provide a lightweight and homogeneous optical element exhibiting favorably weak birefringence and hygroscopicity as well as superior productivity and producing minimal chromatic aberrations by using an organic-inorganic composite material having both the properties of a glass material and those of a plastic material.
To attain the above-described object, the present invention provides an optical element having at least one entrance refracting surface and at least one exit refracting surface. The optical element is formed from an organic-inorganic composite material.
The optical element using an organic-inorganic composite material according to the present invention will be described below.
Recently, attention has being paid to organic-inorganic composite materials having an ultramicro structure in which an inorganic phase is dispersed in the three-dimensional network (matrix) of an organic phase as organic-inorganic hybrid materials [for example, see the August 1998 issue of “Engineering Materials” (Vol. 16, No. 8), pp. 26-31, and the September 1999 issue of “Materials Science” (Vol. 36, No. 5, pp. 39-45]. Such an organic-inorganic hybrid material has both the characteristic features of an organic polymer (e.g. moldability and low density) and those of an inorganic compound (e.g. transparency). The physical properties of the organic-inorganic hybrid material conform to the rules of composition of the organic and inorganic components.
Accordingly, it is possible to obtain a material of high refractive index and low dispersion, which cannot be realized with a plastic material, by appropriately selecting a material for the inorganic phase and a material for the organic phase and selecting an appropriate mixture ratio for the two materials. The organic-inorganic hybrid material thus obtained exhibits superior moldability and hence allows an optical element of desired shape to be obtained by injection molding.
Such an organic-inorganic hybrid material may be produced, for example, by mixing together an organic polymer and a metal alkoxide or a glass precursor (e.g. tetraethoxy silane). Organic-inorganic composite materials obtained in this way include one in which oxygen in the organic polymer and the protons of Si—OH groups in the inorganic polymer bond to each other by hydrogen bonding. Another organic-inorganic composite material has chemical bonding between the organic polymer and the inorganic disperse phase. For example, there is an organic-inorganic composite material having covalent bonding such as —NH—NCOH— as a result of polymerization of —NH
2
group at the end of the inorganic disperse phase with —NCO group.
To ensure the transparency of such an organic-inorganic composite material, it is necessary that the micro structure of the dispersed inorganic phase should have a size not more than the working wavelength. It is desirable that the size of the micro structure should be not larger than 200 nanometers, preferably not larger than 100 nanometers, even more preferably not larger than 20 nanometers.
As the inorganic component of an organic-inorganic composite material, it is preferable to use one selected from among inorganic matters (oxides and nitrides) containing metals belonging to Group IVA in the periodic table of the elements, e.g. Ti and Zr, metals belonging to Group IIIB, e.g. Al, and metals belonging to Group IVB, e.g. Si and Ge. From the viewpoint of ease of use, Si, Ti, Al and Zr are particularly preferable. As a component for imparting high-refractive index properties, it is preferable to use a metal belonging to Group IIIA, e.g. a lanthanoid such as Y or La, or a metal belonging to Group VA, e.g. Nb or Ta, in the form of a composite material combined with Si, Ti, Al, or Zr. It is possible to use metal alkoxides containing these components, derivatives and metal salts thereof, etc.
As the organic component of an organic-inorganic composite material, it is possible to use most organic polymers compatible with the inorganic material used in the process of mixing, gelation, drying and setting and capable of forming hydrogen bonds or covalent bonds with the inorganic material. More specifically, substances containing structures such as —COOH group, —NH
2
group, —OH group and a group containing S have interaction with —H, COOH group, —NH
2
group, —OH group, etc. contained in oligomers formed by hydrolysis of a part of metal alkoxides or derivatives used as inorganic matter. Various organic matters are usable as materials that form hydrogen bonds or covalent bonds with the inorgani
Kinoshita Hiroaki
Morita Yuko
Togino Takayoshi
Olympus Corporation
Yoon Tae H.
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