Optical waveguides – Optical fiber waveguide with cladding – With graded index core or cladding
Patent
1991-05-29
1992-12-29
Ullah, Akm E.
Optical waveguides
Optical fiber waveguide with cladding
With graded index core or cladding
359652, 25037008, G02B 618, G02B 604
Patent
active
051757869
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical transmission article and a method of manufacturing the same, which is useful for optical transmission lines such as near parabolic optical fibers, rod-like convergent lenses, and photosensors.
BACKGROUND ART
Optical transmission articles each with refractive indexes gradually distributed from the center toward the periphery on a cross-section thereof are disclosed in Japanese Examined Patent Publication No. 47-816, Japanese Examined Patent Publication No. 47-28059, and European Patent Publication No. 0208159.
The distributed refractive index type optical transmission article disclosed in Japanese Examined Patent Publication No. 47-816 is made of glass and fabricated by an ion exchange method. This method has a poor productivity and cannot produce an article having an identical shape (an identical length, in particular) and an identical performance. Even with an identical performance, the fabricated distributed refractive index type optical transmission articles have uneven lengths, and thus problems arise with handling thereof.
The distributed refractive index type optical transmission plastic article disclosed in Japanese Examined Patent Publication No. 47-28059 is made by mixing two or more transparent polymers having different refractive indexes and different solubilities with respect to a particular solvent. The mixed polymers are shaped into a rod or a fiber, and immersed in the solvent to extract a part of the polymers from the surface thereof, thereby changing a mixing ratio of the polymers from the surface toward the center thereof Since the refractive index distributed type optical transmission plastic article of this method is made of a mixture of two or more polymers having different refractive indexes, fluctuations in the refractive indexes of the article occur deteriorating the transparency, and causing light scattering, and therefore, the article cannot serve as the distributed refractive index type optical transmission article. Accordingly, little improvement can be expected in the application and development of this method.
European Patent Publication No. 0208159 describes a method in which (A) at least one kind of thermoplastic polymer and (B) a monomer which is compatible with the polymer (A) when polymerized and forms a polymer having a refractive index different from that of the polymer (A), are mixed and formed into a rod-like shape. From the surface of the shaped body, the monomer (B) is volatilized to continuously distribute the monomer (B) from the surface toward the interior of the formed article, and thereafter, the non-polymerized monomer in the shaped body is polymerized to form a distributed refractive index type optical transmission plastic article.
An ideal refractive index distribution curve of the distributed refractive index type optical transmission article is expressed as follows:
This curve is considered to be the same as a curve "a" of FIG. 2.
According to studies and measurements made by the inventor, using an Interfaco interference microscope under conditions to be explained later, however, the distributed refractive index type optical transmission article fabricated according to the above-mentioned method provides a refractive index distribution curve "b" of FIG. 2. In a range of 0.5 r.sub.0 to 0.75 r.sub.0 of radial distances from the center (i.e., in a range of c to d in the figure, with e being an outermost part), the curve b is relatively close to the ideal curve expressed by the equation (1). At the outer and inner sides of the above range, however, the refractive index distribution is greatly deviated from the ideal curve.
When a grid pattern is observed through these optical transmission articles, if the optical transmission article has a refractive index pattern which almost correctly follows the quadratic curve defined by the equation (1), the article will provide a normal grid image as shown in FIG. 3(a). If, however, the refractive index distribution of the optical transmission article deviat
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Applied Optics, vol. 21, No. 15, Aug. 1982, pp. 2739-2746, W. Lama "Optical Properties of Grin Fiber Lens Arrays: Dependence of Fiber Length".
Ishimaru Teruta
Mishina Yoshihiko
Murata Ryuji
Oda Masaaki
Toyoda Nobuhiko
Mitsubishi Rayon Company Ltd.
Ullah Akm E.
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