Abstract: A cladding mode light removal structure includes: an input-side exposure portion where a covering is removed from an end of an input-side optical fiber to expose a cladding of the input-side optical fiber; an output-side exposure portion where a covering is removed from an end of an output-side optical fiber to expose an output-side cladding of the output-side optical fiber; a fusion splice portion at which the input-side exposure portion and the output-side exposure portion are connected by fusion splice; a fiber housing portion having an accommodation space that receives the input-side exposure portion, the output-side exposure portion, and the fusion splice portion; a high refractive index resin having a refractive index equal to or higher than that of the cladding exposed at the input-side exposure portion; and a low refractive index portion of a medium.

Abstract: A cladding mode light removal structure includes: an input-side exposure portion where a covering is removed from an end of an input-side optical fiber to expose a cladding of the input-side optical fiber; an output-side exposure portion where a covering is removed from an end of an output-side optical fiber to expose an output-side cladding of the output-side optical fiber; a fusion splice portion at which the input-side exposure portion and the output-side exposure portion are connected by fusion splice; a fiber housing portion having an accommodation space that receives the input-side exposure portion, the output-side exposure portion, and the fusion splice portion; a high refractive index resin having a refractive index equal to or higher than that of the cladding exposed at the input-side exposure portion; and a low refractive index portion of a medium.

Abstract: The optical fiber fusion splice structure has a fusion splice portion at which the bare fibers exposed from the coverings are connected to each other by fusion splicing, a fiber accommodation portion having a fiber accommodation groove formed along an axis of the optical fibers, and fixation resins for fixing a portion of the coverings on both sides of the fusion splice portion within the fiber accommodation groove. The fiber accommodation groove receives a portion of the optical fibers including the fusion splice portion. The fixation resins are formed so as to fill the fiber accommodation groove in a depth direction. A pipe member that allows an infrared ray to pass therethrough is attached around the fiber accommodation portion so as to surround a space between the fixation resins on both sides of the fusion splice portion within the fiber accommodation groove.

Abstract: The optical fiber fusion splice structure has a fusion splice portion at which the bare fibers exposed from the coverings are connected to each other by fusion splicing, a fiber accommodation portion having a fiber accommodation groove formed along an axis of the optical fibers, and fixation resins for fixing a portion of the coverings on both sides of the fusion splice portion within the fiber accommodation groove. The fiber accommodation groove receives a portion of the optical fibers including the fusion splice portion. The fixation resins are formed so as to fill the fiber accommodation groove in a depth direction. A pipe member that allows an infrared ray to pass therethrough is attached around the fiber accommodation portion so as to surround a space between the fixation resins on both sides of the fusion splice portion within the fiber accommodation groove.

Abstract: Disclosed is an aromatic polyimide film which is well resistant to sagging and dimensional change in the heat treatment. The aromatic polyimide film is formed from a polymer solution which is produced by a polymerization reaction of a biphenyltetracarboxylic acid component and a phenylenediamine component, and characterized in that any rectangle optionally supposed within the film has a ratio between a length of any side and a length of the central portion between the side and a side opposite thereto is in the range of 100:100 to 100:100.15, and a heat shrinkage ratio of the film is not more than 0.3% (0.003) in any direction after the film is heated at 300.degree. C. for 2 hours. A process for the preparation of the above aromatic polyimide film is also disclosed.

Abstract: A dimensionally stable polyimide film and processes for the preparation thereof. The polyimide film is composed of an aromatic polyimide obtained from a solution of a polymer formed by polymerization of a biphenyl-tetracarboxylic acid and a phenylene diamine, wherein the average linear expansion coefficient of the polyimide film in the temperature range of from 50.degree. C. to 300.degree. C. is 0.1.times.10.sup.-5 to 2.5.times.10.sup.-5 cm/cm..degree.C., the ratio of the linear expansion coefficient in the machine direction of the film to the linear expansion coefficient in the transverse direction of the film is in the range of from 1/5 to 4, and the thermal dimension stability expressed by the ratio of the change of the size of the film at normal temperature after the heat treatment where the temperature is elevated to 400.degree. C. from normal temperature and the film is maintained at 400.degree. C. for 2 hours is less than 0.3%.

Abstract: Disclosed is a process for separating 11-cyanoundecanoic acid, cyclohexanone and .epsilon.-caprolactam from a pyrolysis product obtained by pyrolyzing 1,1'-peroxydicyclohexylamine in the presence of steam at a temperature of 300.degree. to 1,000.degree. C. The pyrolysis product is first contacted with a mixture comprised of aqueous ammonia and at least one organic solvent selected from benzene, toluene and xylene, and the so prepared liquid is separated into the oily layer and the aqueous layer. On one hand, the oily layer is distilled to separate cyclohexanone therefrom. On the other hand, the aqueous layer is acidified to a pH of below 4.0 by adding thereto a mineral acid and maintained at a temperature of 40.degree. to 100.degree. C. to separate crude 11-cyanoundecanoic acid in molten form from the aqueous layer, and then, the separated crude molten 11-cyanoundecanoic acid is washed with hot water to extract .epsilon.-caprolactam therefrom.