Abstract: An MCF of one embodiment combines the adoption of a plurality of cores with different refractive indices with suppression of manufacturing costs. The MCF has a glass optical fiber having a plurality of cores and a cladding, and a resin coating. The plurality of cores includes a first core with a high refractive index and a second core with a low refractive index. On a cross-section of the MCF, an arrangement of centers of a plurality of portions has no rotational symmetry about the cross-section center, the portions having a refractive index higher than that of the cladding. Furthermore, a mode leakage adjustment structure is provided to reduce a difference between a cutoff wavelength of a residual higher-order mode in the second core and a cutoff wavelength of a residual higher-order mode in the first core.

Abstract: A method of manufacturing an optical fiber includes heating a distal end portion of an optical fiber preform made of glass; drawing a glass fiber from the distal end portion softened by the heating; and forming a coating layer made of resin on the glass fiber to form an optical fiber. The drawing includes periodically varying a tension that is applied to the glass fiber to vary a diameter of the glass fiber and a residual stress in an axial direction of the glass fiber so as to be in phases opposite to each other along the axial direction.

Abstract: A gain flattening filter includes a first optical fiber that has a core, a first cladding, and a second cladding and that has a uniform composition in a length direction; and a pair of second optical fibers fused to both ends of the first optical fiber. The first optical fiber has a first section in which a slanted refractive index grating is formed and a pair of second sections connecting both ends of the first section to the pair of second optical fibers. The first cladding contains a photosensitive material whose refractive index increases upon irradiation with light having a specific wavelength. In the core, a tensile stress remains in the first section. An average MFD of the second sections is larger than an average MFD of the second optical fibers and smaller than an average MFD of the first section.

Abstract: An optical fiber has a central axis. The optical fiber includes a core made of silica glass and extending along the central axis, a cladding made of silica glass and surrounding the core, the cladding extending along the central axis, and a coating layer made of resin and surrounding the cladding, the coating layer extending along the central axis. An outer diameter of the cladding varies along the central axis. A residual stress in a direction along the central axis varies along the central axis, the residual stress being averaged over the core and the cladding in a cross section perpendicular to the central axis. A deviation from an average value of the outer diameter and a deviation from an average value of the residual stress have signs opposite to each other.

Abstract: An optical fiber includes: a core made of silica glass; and a cladding surrounding the core and made of silica glass. A spectrum of a wavenumber derivative dR(k)/dk of a Raman scattering spectrum R(k) obtained by irradiating the core with pump light having a wavelength 532 nm passes through 0 twice or less in a range of wavenumber from 400 cm?1 to 550 cm?1.

Abstract: A method for producing an optical fiber includes heating and melting an optical fiber preform and drawing the optical fiber preform. In this method for producing an optical fiber, the optical fiber is formed to include a core, a surrounding cladding surrounding a periphery of the core, and an outer cladding surrounding the surrounding cladding. In the drawn optical fiber, a maximum compressive stress of at least 100 MPa or more is applied to an optical waveguide region including at least the core.

Abstract: An optical amplification transmission line of the present disclosure reduces a connection loss between an EDF located upstream of a signal light path and a SMF located downstream of the path, as compared with a conventional optical amplification transmission lines. The optical amplification transmission line includes an EDF and a SMF fusion-spliced to each other. The EDF has an Er-doped core and an F-doped cladding. A core of the SMF is doped with no Er. The ratio (MFD2/MFD1) of the MFD2 of a stationary section of the SMF to the MFD1 of a stationary section of the EDF falls within a range of 1.9 or more and 2.2 or less.

Abstract: A multi-core optical fiber includes a plurality of cores extending along a fiber axis, a cladding including the plurality of cores formed in the cladding, the cladding having rotational symmetry with respect to the fiber axis excluding a portion of the cladding where the plurality of cores are located, and a coating surrounding the cladding and having rotational symmetry with respect to the fiber axis. The multi-core optical fiber has inversion asymmetry with respect to the fiber axis in a side observation image in at least one of two directions each of which is perpendicular to the fiber axis.

Abstract: An optical fiber includes a core made of silica glass, and a cladding surrounding the core and made of silica glass. A product of a center wavenumber k?4 and a half width at half maximum kH4 of a peak of Raman scattered light ?4(T0) obtained by irradiating the core with excitation light having a wavelength of 532 nm is 38000 cm?2 or less.

Abstract: A glass rod manufacturing device includes: a holding portion configured to hold one end of a starting rod; a heating portion configured to heat a bent portion; and a centering jig configured to apply a force in a first direction intersecting an axis to a part of the starting rod that whirls between the bent portion and another end of the starting rod due to rotation of the starting rod about an axis. The centering jig includes: an abutment portion configured to abut against the part; an elastic displacement portion configured to elastically displace the abutment portion in the first direction according to a run-out deviation of whirl of the part; and a slide portion configured to slide the abutment portion in a second direction intersecting the axis and the first direction according to the run-out deviation of whirl of the part.

Abstract: The present disclosure relates to an optical fiber or the like that can be adapted to an optical transceiver for a short wavelength band of 850 nm or more and 1060 nm or less while maintaining compatibility with an SMF of the related art. An optical fiber of one embodiment includes a core, a cladding, and a resin coating, and has a mode field diameter of 8.2 ?m or more and 9.6 ?m or less at a wavelength of 1310 nm, a cable cutoff wavelength of an LP11 mode of 1060 nm or more and 1260 nm or less, and a cable cutoff wavelength of an LP02 mode of 1060 nm or less.

Abstract: A multicore optical fiber of an embodiment has a structure for simultaneously realizing low transmission loss, low fusion splicing loss, and low inter-core crosstalk. The multicore optical fiber includes a plurality of cores comprised of silica glass, a common cladding comprised of silica glass and surrounding the plurality of cores, and a resin coating surrounding the common cladding. The common cladding has a refractive index lower than a refractive index of the plurality of cores. Each of the plurality of cores contains chlorine at 10000 ppm or more in at least part thereof.

Abstract: A multi-core optical fiber includes: a pair of cores; and a cladding that covers both of the pair of cores. A diameter of the cladding is 124 ?m or more and 126 ?m or less. A distance between centers of the pair of cores is 46.5 ?m or less. Cross talk between counter-propagating cores at a wavelength of 1550 nm is ?30 dB/100 km or less.

Abstract: An optical fiber includes a core, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding. A mean relative refractive index difference ?1 of the core, a mean relative refractive index difference ?2 of the inner cladding, and a mean relative refractive index difference ?3 of the outer cladding satisfy a relationship of ?1>?3??2. A ratio r2/r1 of an inner cladding radius r2 to a core radius r1 is 4.5 or higher and 5.5 or lower. A minimum value ?min of a relative refractive index difference is ?0.030% or higher and ?0.010% or lower. A radius rmin at which the relative refractive index difference is the minimum value ?min satisfies a relationship of r1<rmin<r2. (?min??(r1))/(rmin?r1) is ?0.002%/?m or lower, where ?(r1) denotes the relative refractive index difference with the core radius r1.

Abstract: An MCF includes a plurality of cores each extending in a direction along a central axis and a cladding covering each of the plurality of cores. The cladding includes a low refractive index barrier. The low refractive index barrier includes an alkali metal element. A relative refractive index of the low refractive index barrier is lower than an average value of a relative refractive indices of the cladding overall. The core interval is set such that a total sum of the power coupling coefficients between a specific core among the plurality of cores and each of all remaining cores is 2.3×10?4/km or less.

Abstract: A mode-dependent loss measurement device measures a mode-dependent loss of a measurement target optical fiber including a coupled MCF. The device includes a light source, a light receiver, a mode coupled state changer, and an analysis unit. The light source inputs light to an input end of an excitation optical fiber including another coupled MCF. The light receiver detects a sum of powers of outputted light beams from a plurality of core end faces positioned on an output end of the measurement target optical fiber. The mode coupled state changer changes a mode coupled state of the excitation optical fiber. The analysis unit obtains a mode-dependent loss of the measurement target optical fiber from variations in optical powers detected by the light receiver.

Abstract: The MCF of the present disclosure suppresses occurrence of structural abnormality such as air bubbles in the vicinity of a boundary between a marker and a cladding. The MCF includes a glass optical fiber including a plurality of cores, a marker, and a cladding, and a resin coating. On a cross section of the MCF, centers of the plurality of cores and a center of the marker constitute a plane figure having a rotational symmetry of order 1 with respect to a center of the cross section. Moreover, on the cross section, the marker is disposed so as to be located on a circumference of a circle having a center coinciding with the center of the cross section and having the circumference passing through the respective centers of the plurality of cores.

Abstract: An optical fiber has a central axis. The optical fiber includes a core made of silica glass and extending along the central axis, a cladding made of silica glass and surrounding the core, the cladding extending along the central axis, and a coating layer made of resin and surrounding the cladding, the coating layer extending along the central axis. An outer diameter of the cladding varies along the central axis. A residual stress in a direction along the central axis varies along the central axis, the residual stress being averaged over the core and the cladding in a cross section perpendicular to the central axis. A deviation from an average value of the outer diameter and a deviation from an average value of the residual stress have signs opposite to each other.

Abstract: The present disclosure relates to an optical fiber or the like that can be adapted to an optical transceiver for a short wavelength band of 850 nm or more and 1060 nm or less while maintaining compatibility with an SMF of the related art. An optical fiber of one embodiment includes a core, a cladding, and a resin coating, and has a mode field diameter of 8.2 µm or more and 9.6 µm or less at a wavelength of 1310 nm, a cable cutoff wavelength of an LP11 mode of 1060 nm or more and 1260 nm or less, and a cable cutoff wavelength of an LP02 mode of 1060 nm or less.

Abstract: A gain flattening filter includes a first optical fiber that has a core, a first cladding, and a second cladding and that has a uniform composition in a length direction; and a pair of second optical fibers fused to both ends of the first optical fiber. The first optical fiber has a first section in which a slanted refractive index grating is formed and a pair of second sections connecting both ends of the first section to the pair of second optical fibers. The first cladding contains a photosensitive material whose refractive index increases upon irradiation with light having a specific wavelength. In the core, a tensile stress remains in the first section. An average MFD of the second sections is larger than an average MFD of the second optical fibers and smaller than an average MFD of the first section.