Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-10-03
2003-07-15
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S462000, C524S463000, C525S199000, C525S200000
Reexamination Certificate
active
06593415
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a graded-refractive-index optical plastic material (hereinafter sometimes referred to as optical plastic material for short) having high transparency and high heat resistance simultaneously, which conventional optical plastics hardly ever attained, and a method for its production.
The optical plastic material of the present invention may be a light transmission medium such as an optical fiber, or a body material of a light transmission medium such as a preform of an optical fiber.
A light transmission medium which is the optical plastic material of the present invention is free from light scattering and very transparent to light at wavelengths within a wide range from ultraviolet light to near infrared light, since it is made of an amorphous resin, therefore it is useful for optical systems for light of various wavelengths. In particular, the optical plastic material of the present invention provides a light transmission medium with small losses at wavelength of 1300 nm and 1550 nm, at which a trunk vitreous silica fiber is used in the field of optical communication.
A light transmission medium which is the optical plastic material of the present invention has heat resistance, chemical resistance, humidity resistance and nonflammability enough to withstand severe use conditions, for example, in an engine room of an automobile.
A light transmission medium which is the optical plastic material of the present invention is useful as various graded-refractive-index light transmission medium such as a graded-refractive-index optical fiber, a rod lens, an optical waveguide, an optical decoupler, a wavelength multiplexer, a wavelength demultiplexer, an optical attenuator, a light switch, an optical isolator, a light transmitting module, an light receiving module, a coupler, an optical deflector and an optical integrated circuit. Graded-refractive-index means a region wherein the refractive index of a light transmission medium varies continuously in a specific direction. For example, a graded-refractive-index optical fiber shows a refractive index profile that the refractive index parabolically decreases from the center of the fiber along the radii.
When the optical plastic material of the present invention is a body material-of a light transmission medium, it is spun, for example, by hot drawing to prepare a light transmission medium such as a graded-refractive-index optical fiber.
BACKGROUND ART
Heretofore, as resins for graded-refractive-index plastic light transmission medium, optical plastics represented by methyl methacrylate resins, tetrafluoroethylene resins disclosed in WO94/04949 and vinyl fluoride resins have been proposed.
With respect to stepped-refractive-index plastic optical fibers, many proposals have been made to use optical plastics such as a methyl methacrylate resin, a styrene resin, a carbonate resin and a norbornene resin for a core and a fluoropolymer cladding. Japanese Unexamined Patent Publication No. 244007/1990 proposes use of a fluoropolymer core and a fluoropolymer cladding.
The present invention provides an optical plastic material having heat resistance, humidity resistance, chemical resistance and nonflammability required for applications to an automobile, an office automation (OA) equipment, an electrical appliance and the like, which light transmission medium made of a methyl methacrylate resin or a norbornene resin have never attained.
Further, the object of the present invention is to provide a novel optical plastic material which is useful for ultraviolet light (wavelength from 200 nm to 400 nm) and near infrared light (wavelength from 700 nm to 2500 nm), which are unavailable to light transmission medium made of a methacrylate resin, a carbonate resin and a norbornene resin, and has low light transmission losses in a wide transmission zone and a method of its production.
DISCLOSURE OF INVENTION
The present inventors have conducted extensive researches taking the above-mentioned problems into consideration, and consequently found that a fluoropolymer which substantially has no C—H bond is the most suitable to provide heat resistance, humidity resistance, chemical resistance and nonflammability and eliminate C—H bonds (namely carbon-hydrogen bonds) which absorb near infrared light. The fluoropolymer has C—F bonds (namely carbon-fluorine bonds) instead of C—H bonds.
When a substance is exposed to light, a certain interatomic bond absorbs preferentially light of wavelength resonant with its stretching vibration and deformation vibration. Conventional polymeric materials used for plastic optical fibers are mostly compounds having C—H bonds. Such polymeric materials which basically have C—H bonds show the main absorption bands at a shorter wavelength (3400 nm) in the infrared region, since a hydrogen atom is so light as to easily vibrate. Accordingly, in the near infrared to infrared region (from 600 to 1550 nm), which is the wavelength region of a light source, relatively lower harmonic absorption peaks due to the stretching vibration of C—H bonds appears at intervals and they are greatly responsible for absorption loss.
If hydrogen atoms are substituted by fluorine atoms, these harmonic absorption peaks shift to longer wavelengths, and the amount of absorption in the near infrared region decreases. In the case of a PMMA (polymethyl methacrylate) having C—H bonds, the absorption loss attributable to the C—H bonds is estimated theoretically to be 105 dB/km at a wavelength of 650 nm and at least 10000 dB/km at a wavelength of 1300 nm.
On the contrary, in the case of a material in which hydrogen atoms are substituted with fluorine atoms, there is substantially no absorption loss at a wavelength of 650 nm, and the absorption loss at a wavelength of 1300 nm, which is between the sixth and the seventh overtones, is in the order of 1 dB/km and therefore negligible. For this reason, we propose to use a compound having C—F bonds.
It is also preferred to eliminate functional groups such as a carboxyl group and a carbonyl group which inhibit heat resistance, humidity resistance, chemical resistance and nonflammability. Further, since the presence of a carboxyl group-results in absorption of near infrared light, and the presence of a carbonyl group results in absorption of ultraviolet light, it is preferred to eliminate these groups. In addition, in order to reduce a transmission loss due to light scattering, it is important to use an amorphous polymer.
In the case of a stepped-refractive-index optical fiber, multimodal light is propagated in it, by being reflected on the interface between the core and the cladding. Therefore, mode dispersion occurs, and as a result, the transmission zone decreases. However, a graded-refractive-index optical fiber hardly causes mode dispersion, and therefore, the transmission zone increases.
The present inventors found out an optical plastic material composed of an amorphous fluoropolymer which substantially has no C—H bond, especially a fluoropolymer having a cyclic structure on its main chain, and a material which differs from the polymer in refractive index, wherein the concentration of the material shows a gradient in a specific direction and a method of its production for the first time, and achieved the following present inventions (1) to (2).
(1) A graded-refractive-index optical plastic material composed of an amorphous fluoropolymer (a) which substantially has no C—H bond and at least one material (b) which differs from the fluoropolymer (a) in refractive index by at least 0.001, wherein the material (b) is so distributed in the fluoropolymer (a) as to have a concentration gradient in a specific direction.
(2) A method of producing a graded-refractive-index optical plastic material, which comprises melting an amorphous fluoropolymer (a) which substantially has no C—H bond, injecting at least one material (b) which differs from the fluoropolymer (a) in refractive index by at least 0.001, or the fluoropolymer (a) containing the material (b) at the center of the melt of the f
Koike Yasuhiro
Naritomi Masaki
Koike Yasuhiro
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pezzuto Helen L.
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