Abstract: The present invention includes a sheet material, a first optical fiber, a second optical fiber optically coupled to the first optical fiber in portions thereof, and an optical fiber coupler constituted in the portions where the two optical fibers are coupled, and those of the first and second optical fibers, and the optical fiber coupler are integrally held in the sheet material.

Abstract: A core 2 is co-doped with Ge in a general concentration equivalent to that in a core of an optical fiber to be connected as well as Sn and Al in predetermined concentrations. A glass part F including the core and a cladding 3 is coated with a primary coat layer 4 of a UV transmitting resin which transmits UV of 240 nm through 270 nm but cures by absorbing UV of a shorter wavelength band than 240 nm or a longer wavelength band than 270 nm. A grating is written in the core by irradiating the core with UV through the primary coat layer. The primary coat layer is covered with a secondary coat layer 7 of a resin having a negative coefficient of linear expansion so as to cancel and suppress expansion/shrinkage of the glass part in accordance with temperature change derived from the positive coefficient of linear expansion.

Abstract: A long period grating (8) by which an excitation light propagated through the 2nd core (4) of a double-core type optical fiber composed of the 2nd core (4) formed on the outer circumference of the 1st core (2) is guided into the 1st core (2) is formed on the 1st core (2) to improve an excitation efficiency.

Abstract: A structure for retaining an optical fiber, capable of not only handling a long optical fiber as one piece without causing the optical fiber as a whole to get loose but also reducing an area occupied by the optical fiber and retaining the same stably without causing micro-bending thereof to occur, wherein the optical fiber (1) is arranged so as to form planarly staggered turning portions thereof without causing intersecting parts to occur, a plurality of similar planarly staggered turning portions of the optical fiber being laminated in the same position in the direction of the thickness thereof which is at right angles to a plane on which the optical fiber is arranged, the resultant optical fiber (1) being generally retained in a sheet-like state by a fixing material (2), such as a bonding agent and a film.

Abstract: The present invention includes a sheet material, a first optical fiber, a second optical fiber optically coupled to the first optical fiber in portions thereof, and an optical fiber coupler constituted in the portions where the two optical fibers are coupled, and those of the first and second optical fibers, and the optical fiber coupler are integrally held in the sheet material.

Abstract: An optical fiber coupler for optical fiber amplifier use in the field of optical communications is provided. The optical fiber coupler comprises: a rare earth-doped fiber as an optical amplifying element; a quasi rare earth-doped fiber for entrance of input signal light; a fused-stretch fiber portion as a multiplexing element which connects a part of the rare earth-doped fiber and a parts the quasi rare earth-doped fiber, wherein the fused-stretch fiber portion formed by stretched a fused mixture of parts of the rare earth-doped fiber and the quasi rare earth-doped fiber; and a single mode fiber which is jointed at a fused joint portion to another shortened rare earth-doped fiber connected to the fused-stretch fiber portion on a side connected by the quasi rare earth-doped fiber. The quasi rare earth-doped fiber has substantially equal propagation constant to the rare earth-doped fiber without substantially containing rare earth elements.