Abstract: A method for manufacturing an optical fiber by drawing an optical fiber preform softened by heating, includes cooling the optical fiber at a cooling rate of not more than 4000° C. per second at a temperature of 1200 to 1400° C. of the optical fiber; and cooling the optical fiber at a cooling rate of not more than 8000° C. per second at a temperature of 850 to 1200° C. of the optical fiber. A drawing rate of the optical fiber is not less than 1000 meters per minute.

Abstract: An optical fiber having a length of 1 km or more with average transmission loss in a wavelength band of 1383 nm being less than average transmission loss in a wavelength band of 1310 nm, wherein a maximum value of any 1 km section loss in the wavelength band of 1383 nm does not exceed the average transmission loss by 0.03 dB/km or more.

Abstract: Two or more optical waveguides are placed in a treatment vessel. The optical waveguides in the treatment vessel are treated with a chemical substance containing at least one of deuterium, hydrogen, and a compound thereof. The treating includes causing molecules of the chemical substance to diffuse into the optical waveguides, causing the molecules of the chemical substance that have diffused into the optical waveguides to react with structural defects that exist in a portion, through which light propagates, of the optical waveguides, and removing from the optical waveguides molecules of the chemical substance that do not react with the structural defect.

Abstract: A protective cover is detachably fixed onto a spool to protect an optical fiber wound on the spool. The protective cover includes a pair of half-cylindrical cover members coupled together by a hinge and locked together by a locking mechanism. When an external force allows a pair of hinge members of the hinge to abut together, edges of the cover members are apart from each other at an angle of 2 to 7 degrees as viewed with respect to the center of the hinge. The edges of the cover members are then abut together by an additional external force to lock the locking mechanism.

Abstract: A protective cover is detachably fixed onto a spool to protect an optical fiber wound on the spool. The protective cover includes a pair of half-cylindrical cover members coupled together by a hinge and locked together by a locking mechanism. When an external force allows a pair of hinge members of the hinge to abut together, edges of the cover members are apart from each other at an angle of 2 to 7 degrees as viewed with respect to the center of the hinge. The edges of the cover members are then abut together by an additional external force to lock the locking mechanism.

Abstract: An optical fiber having a length of 1 km or more with average transmission loss in a wavelength band of 1383 nm being less than average transmission loss in a wavelength band of 1310 nm, wherein a maximum value of any 1 km section loss in the wavelength band of 1383 nm does not exceed the average transmission loss by 0.03 dB/km or more.

Abstract: A method for manufacturing an optical fiber by drawing an optical fiber preform softened by heating, includes cooling the optical fiber at a cooling rate of not more than 4000° C. per second at a temperature of 1200 to 1400° C. of the optical fiber; and cooling the optical fiber at a cooling rate of not more than 8000° C. per second at a temperature of 850 to 1200° C. of the optical fiber. A drawing rate of the optical fiber is not less than 1000 meters per minute.

Abstract: A method for manufacturing an optical fiber by drawing an optical fiber preform softened by heating, includes cooling the optical fiber at a cooling rate of not more than 4000° C. per second at a temperature of 1200 to 1400° C. of the optical fiber; and cooling the optical fiber at a cooling rate of not more than 8000° C. per second at a temperature of 850 to 1200° C. of the optical fiber. A drawing rate of the optical fiber is not less than 1000 meters per minute.

Abstract: Two or more optical waveguides are placed in a treatment vessel. The optical waveguides in the treatment vessel are treated with a chemical substance containing at least one of deuterium, hydrogen, and a compound thereof. The treating includes causing molecules of the chemical substance to diffuse into the optical waveguides, causing the molecules of the chemical substance that have diffused into the optical waveguides to react with structural defects that exist in a portion, through which light propagates, of the optical waveguides, and removing from the optical waveguides molecules of the chemical substance that do not react with the structural defect.

Abstract: An optical fiber having a length of 1 km or more with average transmission loss in a wavelength band of 1383 nm being less than average transmission loss in a wavelength band of 1310 nm, wherein a maximum value of any 1 km section loss in the wavelength band of 1383 nm does not exceed the average transmission loss by 0.03 dB/km or more.

Abstract: The present invention provides a method of manufacturing a porous preform for an optical fiber, including the steps of removing impure particles from silica powder while being stirred in an alkaline liquid phase, and obtaining the porous preform for an optical fiber by applying the powder forming method to the silica powder used as a main raw material. The present invention further has a method of manufacturing a porous preform for an optical fiber, including the step of preparing a forming material by adding fine particles having a particle diameter satisfying the following formula (I) to the silica powder, and obtaining the porous preform by applying the powder forming method to the forming material: ##EQU1## wherein d: diameter of fine particles, and D: diameter of silica powder.

Abstract: The present invention provides a method of manufacturing an optical fiber preform having the steps of disposing a rod member made of a silica-based material within a cavity of a mold, followed by loading a molding material within the mold cavity, and applying pressure to the mold from the outside to form a porous layer on the surface of the rod member and, thus, to obtain a porous preform, wherein at least one end portion of the rod member extends outside the mold cavity in the step of applying pressure to the mold. The particular method permits manufacturing a high quality porous preform free from splits or cracks, making it possible to obtain a high quality optical fiber preform free from residual bubbles.

Abstract: The method of manufacturing a silica glass preform comprises the steps of inserting a rod-like member mainly containing a ductile material, into a forming space of a mold, charging the remaining space of the forming space with a forming material containing silica glass powder or doped silica glass powder, compressing the mold charged with the forming material from outside such as to form a porous glass body of the forming material around the rod-like member, removing the rod-like member from the porous glass body, inserting a glass rod into the hole formed after removal of the rod-like member, purifying said porous glass body in which the glass rod is inserted, and consolidating said porous glass body purified in the above purifying step.