Abstract: A mask having a center hole for passing through a center fiber, which is one of multiple fibers, and multiple surrounding holes for passing through surrounding fibers, which are the remainder of the multiple fibers, and a stress adjusting unit for holding stresses generated in the center fiber and surrounding fibers to a desired constant value, respectively, are installed. The surrounding fibers are rotated around the center fiber by rotating the mask. The center fiber and the surrounding fibers that have been twisted around the center fiber are heated with a heating apparatus and drawn. The center fiber and the surrounding fibers are fixed using a clamp installed between the stress adjusting unit and the heating apparatus.

Abstract: A multi-branching optical coupler outputs input light by branching the input light into multiple fibers. This multi-branching optical coupler has a center fiber positioned at the center of the multiple fibers and multiple surrounding fibers installed around the circumference of the center fiber such that the distance between any two adjacent surrounding fibers is substantially constant. The light input to the input end of the center fiber is branched into the output end of the center fiber and the surrounding fibers. The center fiber has a core that extends from the input end to the output end, and a clad formed around the core. The totality of fibers has a coupled region in which all of the surrounding fibers are fused to the center fiber. The center fiber and the surrounding fibers may be installed substantially parallel to each other and linearly. As an alternative, the surrounding fibers may be twisted co-axially about the center fiber.

Abstract: Herein disclosed is an optical amplifier which permits sufficient reduction of light-transmission loss when it is incorporated into an optical communication system as a part thereof. The optical amplifier comprises an optical fiber 8 for amplification having a length sufficient for stimulated emission through excitation by an excitation laser beam and sufficient for amplifying a transmitted laser beam; an optical fiber 17 for transmission; and an optical wavelength division multiplexer 6 formed by partially fusing, under drawing conditions, the optical fibers 8 and 17 at a portion in the proximity to the light-incident end of the fiber 8 for amplification. The optical amplifier comprises the optical wavelength division multiplexer 6 formed from a part of the optical fiber 8 for amplification and, therefore, permits substantial reduction in the number of fused portions required for the connection thereof to an optical communication system upon incorporation thereof into the system.

Abstract: A wide wavelength range-coupler whose light-branching ratio shows low wavelength-dependency, which is provided with a well-shaped light-coupling portion and excellent optical properties and which can easily be connected to other optical fibers as well as a method for the production thereof are herein provided. The light-coupling portion 3 of the optical fiber coupler is formed by fusing and orientating a plurality of single mode optical fibers 1 and 2 partially arranged parallel to one another and these optical fibers 1 and 2 have cores 1a and 2a which are different from one another in diameter, but are substantially identical in the outer diameter of the clad and in the mode field diameter. Each single mode optical fiber as a material for the coupler has a core diameter and a mode field diameter which are correlated through a quadratic function and therefore, there can be selected two optical fibers 1 and 2 which are identical to one another in the mode field diameter, but differ in the core diameter.

Abstract: In an optical fiber coupler comprising a plurality of optical fibers bundled together and a light-coupling portion which is formed by partially fusing and drawing these bundled fibers and which permits branching of light rays incident upon one of these fibers into the other fibers at a predetermined branching ratio, the optical fiber coupler has a difference between the branching ratio thereof determined immediately after the fusing and drawing operation and that determined after accommodating the coupler in a protective case and then adhering it to the case, equal to or less than 5%. Such an optical fiber coupler can be produced by bundling a plurality of optical fibers 1 and 2, fusing and drawing a part of the bundled optical fibers with heating, fixing the relative positions of these optical fibers 1 and 2 immediately after the fusing and drawing operation and then accommodating in and fixing to a protective case.

Abstract: An improvement is proposed for decreasing the variation in the coupling ratio of an optical fiber coupler after a heat shock test. In an optical fiber coupler which is an elongated intergral body formed by fusing a plural number of optical fibers side-by-side consisting of two straightly columnar parts and a biconical part therebetween formed by drawing and adhesively bonded to a reinforcing base with a coating layer of an adhesive therebetween, the improvement can be achieved by limiting the zone where the coating layer of an adhesive to the surface of each of the straightly columnar parts within a range from the boundary between the straightly columnar part and the biconical part to a point 8 mm apart from the boundary.

Abstract: Herein provided is a support member for supporting an optical fiber coupler formed by arranging a plurality of optical glass fibers parallel to one another, then welding and drawing a part thereof wherein a long and thin reinforcing material of quartz whose external is at least partially formed into a circular shape is accommodated in a cylindrical metal case while coming the material into contact with the inner wall of the case; the optical fiber coupler is arranged along the reinforcing material; a portion of the optical fiber coupler which is not welded and drawn comes in contact with the reinforcing material and a part of the contact portion of the optical coupler is fixed to the material with an adhesive.