Abstract: According to one embodiment, in an optical fiber bundle, in the cross section, arrangement of cores of a first multi-core fiber and arrangement of cores of a second multi-core fiber are the same as each other, arrangement of cores of a third multi-core fiber and arrangement of cores of a fourth multi-core fiber are the same as each other, and when the first multi-core fiber is rotated 180° in a circumferential direction of the first multi-core fiber, the arrangement of the cores of the first multi-core fiber is the same as the arrangement of the cores of the fourth multi-core fiber.

Abstract: An optical fiber connection structure includes: a tubular member; a first collimator attached to a first end of the tubular member in an axial direction; and a second collimator attached to a second end of the tubular member. The first collimator includes a first optical fiber, a first ferrule, a first lens, and a first sleeve. The second collimator includes a second optical fiber, a second ferrule terminating the second optical fiber, a second lens, and a second sleeve. The first sleeve is fixed to the first end via adhesive in a state where the first lens faces the tubular member, and the second sleeve is fixed to the second end via adhesive in a state where the second lens faces the tubular member. An outer diameter of the second ferrule is larger than that of the second lens.

Abstract: An optical connection structure includes a MCF, a first ferrule, a plurality of optical fibers, and a second ferrule. The MCF includes first cores and a first cladding. The first ferrule has a first inner hole and a first ferrule end surface. Each optical fiber optically connected to the MCF includes a second core and a second cladding. The second ferrule has a second inner hole housing tip parts of the optical fibers, and a second ferrule end surface. The second ferrule fixes the tip parts of the optical fibers in the second inner hole by an adhesive. The adhesive is packed in the second inner hole such that a surface of the adhesive is recessed from the second ferrule end surface into the second inner hole. A refractive-index matching material is applied in a space sealed by the first ferrule end surface and the second ferrule end surface.

Abstract: An optical fiber bundle connector includes a plurality of optical fibers, a plastic tube, a ferrule, an intermediate member, a frame member, and a pressing member. A portion of each of the plurality of optical fibers is inserted in the plastic tube. The ferrule extends in a first direction and holds tip portions of the plurality of optical fibers. The intermediate member has a cylindrical shape. The plurality of optical fibers are inserted in the intermediate member. The intermediate member connects the plastic tube and the ferrule. The frame member accommodates at least a portion of the ferrule, the intermediate member, and at least a portion of the plastic tube. The pressing member is disposed around the intermediate member and configured to press the ferrule toward a tip side of each of the plurality of optical fibers against the frame member.

Abstract: In each of the plurality of optical fibers, a second diameter portion has a diameter larger than that of a first diameter portion. A tapered portion connects the first diameter portion and the second diameter portion by a tapered surface. In a fiber accommodating, a second accommodating portion has an inner diameter larger than that of a first accommodating portion. Each first diameter portion is located in the first accommodating portion. Each second diameter portion is located in the second accommodating portion. The second accommodating portion includes a plurality of regions divided by imaginary planes perpendicular to the first direction. The tapered portions of the optical fibers adjacent to each other among the plurality of optical fibers are located in the different regions among the plurality of regions.

Abstract: An optical fiber array includes a plurality of single-core fibers each having a core and a cladding and each having, in a distal end surface thereof, a beam expanding portion capable of expanding a mode field diameter (MFD) of light propagating in the core, and a ferrule having an optical fiber holding hole into which the plurality of single-core fibers are inserted, and an end surface in which the optical fiber holding hole opens. A cladding diameter of each of single-core fiber in the beam expanding portion decreases toward the distal end surface. The optical fiber holding hole has a tapered portion whose inner diameter decreases toward the end surface and against which the distal end surfaces abut.

Abstract: An optical fiber connection structure includes: a tubular member; a first collimator attached to a first end of the tubular member in an axial direction; and a second collimator attached to a second end of the tubular member. The first collimator includes a first optical fiber, a first ferrule, a first lens, and a first sleeve. The second collimator includes a second optical fiber, a second ferrule terminating the second optical fiber, a second lens, and a second sleeve. The first sleeve is fixed to the first end via adhesive in a state where the first lens faces the tubular member, and the second sleeve is fixed to the second end via adhesive in a state where the second lens faces the tubular member. An outer diameter of the second ferrule is larger than that of the second lens.

Abstract: An optical fiber connection structure includes: a multi-core fiber; a plurality of single-core fibers; a first lens having a focal length of f1 (mm); and a second lens having a focal length of f2 (mm). A core pitch of the multi-core fiber is P1 (?m), a mode field diameter on the first end face of each core is MFD1 (?m), a core pitch of multiple single-core fibers is P2 (?m), a mode field diameter of a light beam on the second end face of each core is MFD2 (?m), and the following formulas are satisfied. (P1/P2)×0.9?f1/f2?(P1/P2)×1.1, and (P1/P2)×0.9?MFD1/MFD2?(P1/P2)×1.

Abstract: A plurality of optical fibers are kept in a fiber accommodating portion. In each of the optical fibers, a second diameter portion has a diameter larger than that of a first diameter portion. A second accommodating portion of the fiber accommodating portion has an inner diameter larger than that of a first accommodating portion of the fiber accommodating portion. An inner diameter transition portion of the fiber accommodating portion locates between the first accommodating portion and the second accommodating portion through a tapered surface. The first diameter portion of each of the optical fibers is located in the first accommodating portion, in the inner diameter transition portion, and in the second accommodating portion. Each of the optical fibers is separated from an inner surface of the ferrule in the inner diameter transition portion.

Abstract: A wavelength multiplexing/demultiplexing device includes a first collimator, an M number of second collimators, and the M number of filters. The filters have transmission wavelength bands differing from each other. An optical path connecting the first collimator and the second collimator in first order to each other passes through the filter in first order. An optical path connecting a surface opposite to a multilayer film of the filter in mth (m=1, . . . , M) order and the second collimator in (m+1)th order to each other passes through the filter in (m+1)th order. The filter in (m+1)th order is optically coupled on the surface opposite to the multilayer film to the filter in mth order and is optically coupled on a surface of the multilayer film to the second collimator in (m+1)th order.

Abstract: An optical fiber module is disclosed. The optical fiber module includes a first optical fiber as an MCF, a plurality of second optical fibers as MCFs, a first unit, and a second unit. The first unit has an hole holding the first optical fiber and a plurality of holes respectively holding the second optical fibers. These holes are independent of each other. Each optical fiber has a first part and a second part. An outer surface of a cladding of the first part is coated with a resin. An outer surface of a cladding of the second part is exposed from the resin. The first unit holds the first part. The second unit holds the second part. A boundary between the first part and the second part is positioned in a space between the first unit and the second unit.

Abstract: An optical connection structure includes a MCF, a first ferrule, a plurality of optical fibers, and a second ferrule. The MCF includes first cores and a first cladding. The first ferrule has a first inner hole and a first ferrule end surface. Each optical fiber optically connected to the MCF includes a second core and a second cladding. The second ferrule has a second inner hole housing tip parts of the optical fibers, and a second ferrule end surface. The second ferrule fixes the tip parts of the optical fibers in the second inner hole by an adhesive. The adhesive is packed in the second inner hole such that a surface of the adhesive is recessed from the second ferrule end surface into the second inner hole. A refractive-index matching material is applied in a space sealed by the first ferrule end surface and the second ferrule end surface.

Abstract: An optical fiber array includes a plurality of single-core fibers each having a core and a cladding and each having, in a distal end surface thereof, a beam expanding portion capable of expanding a mode field diameter (MFD) of light propagating in the core, and a ferrule having an optical fiber holding hole into which the plurality of single-core fibers are inserted, and an end surface in which the optical fiber holding hole opens. A cladding diameter of each of single-core fiber in the beam expanding portion decreases toward the distal end surface. The optical fiber holding hole has a tapered portion whose inner diameter decreases toward the end surface and against which the distal end surfaces abut.

Abstract: An optical connection structure includes a first spatial multiplex transmission line, a second spatial multiplex transmission line, a first lens arrangement, a second lens arrangement and a first beam diameter conversion portion. The first spatial multiplex transmission line has a plurality of first transmission lines. The second spatial multiplex transmission line has a plurality of second transmission lines. The first lens arrangement is optically coupled with the first spatial multiplex transmission line. The second lens arrangement is optically coupled with the second spatial multiplex transmission line. The first beam diameter conversion portion has a first end face and a second end face and arranged between the first spatial multiplex transmission line and the first lens arrangement. The first beam diameter conversion portion is configured such that an optical diameter at the second end face is larger than an optical diameter at the first end face.

Abstract: An optical fiber amplifier comprising a first optical fiber, a second optical fiber, a third optical fiber, and an excitation light source, is disclosed. Each optical fiber has cores and a cladding surrounding the cores. The third optical fiber transmits excitation light used for signal amplification in the second optical fiber. A rare-earth element is doped to the second optical fiber that amplifies an optical signal propagating therein by the excitation light. The third optical fiber includes a reduced-diameter portion. A distance between the cores of the third optical fiber in the reduced-diameter portion is shorter than a distance between the cores in other portion of the third optical fiber, and the excitation light entering from the excitation light source to one of the cores of the third optical fiber is mode-coupled with another core of the third optical fiber to distribute the excitation light in the reduced-diameter portion.

Abstract: An optical fiber amplifier comprising first, second and third optical fibers, and first, second and third lenses, is disclosed. First cores of the first optical fiber and second cores of the second optical fiber have homothetic arrangement each other in the arrangement of outer cores. The first core has a mode field diameter MFD1S when transmitting an optical signal and a core pitch P1, and the first lens has a focal distance f1S at the wavelength of the optical signal. The second core has a mode field diameter MFD2S when transmitting the optical signal and a core pitch P2, and the second lens has a focal distance f2S at the wavelength. The MFD1S of each first core is within ±25% of MFD2S×(P1/P2) of the corresponding second core, and the MFD1S of each first core is within ±25% of MFD2S×(f1S/f2S) of the corresponding second core.

Abstract: An optical fiber module is disclosed. The optical fiber module includes a first optical fiber as an MCF, a plurality of second optical fibers as MCFs, a first unit, and a second unit. The first unit has an hole holding the first optical fiber and a plurality of holes respectively holding the second optical fibers. These holes are independent of each other. Each optical fiber has a first part and a second part. An outer surface of a cladding of the first part is coated with a resin. An outer surface of a cladding of the second part is exposed from the resin. The first unit holds the first part. The second unit holds the second part. A boundary between the first part and the second part is positioned in a space between the first unit and the second unit.

Abstract: An optical connector comprises a first optical waveguide including a plurality of cores each extending along a first direction, the first optical waveguide having a first end face, wherein the cores are arranged on the first end face at positions except a position of a central axis of the first optical waveguide, and a first lens having a second end face and a third end face in the first direction, the first lens having an optical axis extending along the first direction. The first optical waveguide and the first lens are arranged so that the central axis of the first optical waveguide coincides with the optical axis of the first lens. The second end face is positioned facing the first end face, and the third end face extends along a plane perpendicular to an optical axis of the first optical waveguide.

Abstract: An optical connection structure includes a first spatial multiplex transmission line, a second spatial multiplex transmission line, a first lens arrangement, a second lens arrangement and a first beam diameter conversion portion. The first spatial multiplex transmission line has a plurality of first transmission lines. The second spatial multiplex transmission line has a plurality of second transmission lines. The first lens arrangement is optically coupled with the first spatial multiplex transmission line. The second lens arrangement is optically coupled with the second spatial multiplex transmission line. The first beam diameter conversion portion has a first end face and a second end face and arranged between the first spatial multiplex transmission line and the first lens arrangement. The first beam diameter conversion portion is configured such that an optical diameter at the second end face is larger than an optical diameter at the first end face.

Abstract: A connector plug according to an embodiment includes a flange attached to a ferrule of an optical connector, a plug frame containing the flange, and a first spring and a second spring interposed between the flange and the plug frame. The flange has outer surfaces, the plug frame has inner surfaces, the first spring is interposed between the outer surface and the inner surface, the second spring is interposed between the outer surface and the inner surface, the outer surface and the inner surface are in contact with each other, and the outer surface and the inner surface are in contact with each other.