Abstract: A silica optical fiber is provided, which contains a pure-silica core and a cladding layer formed on the pure-silica core, wherein the pure-silica core contains a C element and has a content of elements belonging to the third period-the seventh period of the periodic table, except Si element that constitutes the quartz structure, of not more than 100 ppm. The present invention can provide a silica optical fiber superior in the resistance to high energy electromagnetic waves such as UV light and &ggr;-rays.

Abstract: A silica optical fiber is provided, which contains a pure-silica core and a cladding layer formed on the pure-silica core, wherein the pure-silica core contains a C element and has a content of elements belonging to the third period-the seventh period of the periodic table, except Si element that constitutes the quartz structure, of not more than 100 ppm. The present invention can provide a silica optical fiber superior in the resistance to high energy electromagnetic waves such as UV light and &ggr;-rays.

Abstract: In an optical amplifier apparatus for amplifying an incident signal light having wavelengths of 1.06 &mgr;m band, a first optical isolator makes an incident signal light pass therethrough in one direction from an input end to an output end. An optical fiber includes a core mainly composed of silica glass and doped with a predetermined rare-earth element and the other elements, and a cladding of silica glass, and transfers in a single mode the signal light output from the first optical isolator. An optical multiplexer multiplexes an excitation light having an excitation wavelength of 0.8 &mgr;m band with the signal light transferred by the optical fiber, by outputting the excitation light to the optical fiber, and further transfers and outputs the signal light having wavelengths of 1.06 &mgr;m band amplified by induced emission in the optical fiber due to the rare-earth element excited by the excitation light.

Abstract: The present invention relates to an energy transmission optical fiber which is a medium for transmitting high-energy beams within an ultraviolet range such as laser beams. Since an optical fiber according to the present invention comprises a core formed of pure silica and a clad having a graded index type distribution of refractive index and said clad is disposed on an interface between the core and the clad where many structural defects are generated, the transmission loss is not increased even after the transmission of high-energy beams for a long time. In addition, since the optical fiber according to the present invention comprises the core formed of pure silica having a high melting point, the high-energy beams can be transmitted without generating a melting fracture in the core.

Abstract: A composition for filling the spaces in bores penetrating walls and floors of buildings and having electric wires and cables extending therethrough or for filling the clearances at the joints of interior finishing materials of buildings. The composition comprises (a) 100 parts by weight of a curable polychloroprene in a liquid state at room temperature, (b) about 200 to about 700 parts by weight of a hydrated metallic oxide, and (c) about 20 to about 100 parts by weight of a heat-resistant fibrous material. The components (b) and (c) are contained in a combined amount of at least about 250 parts by weight per 100 parts by weight of the component (a). The composition will not soften, sag or drip in molten drops even when subjected to the high-temperature conditions of a fire, and gives a tough residual product retaining the original shape when burned and ashed, effectively preventing the spread of fire and assuring outstanding smoketightness.