Abstract: An optical amplifier is provided in which adjacent ones of a plurality of cores each containing a rare-earth element and included in an amplifying multi-core optical fiber (MCF) serve as coupled cores at an amplifying wavelength, a connecting MCF is connected to the amplifying MCF, a pump light source is connected to the connecting MCF, and the pump light source pumps the rare-earth element in the amplifying MCF through the connecting MCF.

Abstract: The present embodiment relates to an optical amplifier and the like having a structure for enabling efficient use of pumping light while avoiding complication of a device structure. In such an optical amplifier, since pumping light from a pumping light source is supplied to each core of an amplification MCF, a coupling MCF in which adjacent cores form a coupled core is arranged between the amplification MCF and the pumping light source. The pumping light source is optically connected to a specific core of the coupling MCF, and pumping light is coupled from the specific core to remaining cores except the specific core in the coupling MCF before pumping light is supplied to each core of the amplification MCF. This enables coupling of pumping light between optically connected cores between the amplification MCF and the coupling MCF.

Abstract: A mode-dependent loss measurement device according to an embodiment of the present disclosure measures a mode-dependent loss of a measurement target optical fiber including a coupled MCF. The device includes a light source, a light receiver, mode coupled state change means, 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 change means 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 present invention relates to a method and device for measuring optical nonlinearity of an optical fiber to be measured comprising a plurality of cores having mutually coupled waveguide modes. The method includes, at least, preparing a laser light source emitting laser light and a detecting unit determining an optical intensity, inputting laser light into a specific core of the optical fiber to be measured, determining the intensity of a specific wavelength component caused by optical nonlinearity among the reflective light components from the optical fiber to be measured, and determining optical nonlinearity of the optical fiber to be measured on the basis of the intensity of the specific wavelength component.

Abstract: An optical fiber includes a core and a cladding. The core contains silica glass and includes a central portion (part having a diameter of 0.5 ?m or more and 4 ?m or less). The central portion has the central axis of the optical fiber. The cladding contains silica glass and surrounds the core. The core contains chlorine. A chlorine concentration averaged in the entire core is 10,000 ppm or more and 50,000 ppm or less. The chlorine concentration averaged in the entire core minus a chlorine concentration averaged in the central portion is 4,500 ppm or more and 13,500 ppm or less.

Abstract: An optical fiber according to an embodiment includes: a core; an inner cladding surrounding the core and having a refractive index smaller than a refractive index of the core; an outer cladding surrounding the inner cladding and having a smaller refractive index than the refractive index of the core and having a refractive index greater than the refractive index of the inner cladding, in which a ratio of a caustic radius to a MAC-value (caustic radius/MAC-value) at a bending radius of 10 mm at a wavelength of 1625 nm is 2.70 ?m or more.

Abstract: One embodiment of the present disclosure relates to an SFG (slanted fiber grating) that can easily realize a high-performance gain equalizer. The SFG includes an optical fiber comprised of silica-based glass and including a core, a first cladding containing a photosensitive material, and a second cladding. A specific section between two different points arranged along a fiber axis in the optical fiber is configured with a first region, a pair of second regions, and a third region. The first region includes a slanted Bragg grating provided in a region as the first cladding. The pair of second regions are arranged to sandwich the first region. The third region is disposed to sandwich both the first region and the pair of second regions. An MFD at a wavelength of 1.55 ?m in the third region is smaller than an MFD at a wavelength of 1.55 ?m in the first region.

Abstract: An optical fiber includes a core and a cladding. The core contains silica glass and includes a central portion (part having a diameter of 0.5 ?m or more and 4 ?m or less). The central portion has the central axis of the optical fiber. The cladding contains silica glass and surrounds the core. The core contains chlorine. A chlorine concentration averaged in the entire core is 10,000 ppm or more and 50,000 ppm or less. The chlorine concentration averaged in the entire core minus a chlorine concentration averaged in the central portion is 4,500 ppm or more and 13,500 ppm or less.

Abstract: An optical fiber line of one embodiment comprises an HNLF, an SMF, and an MFD transition portion. The MFD transition portion includes end portions of both the HNLF and the SMF facing with a fusion point thereof, and is a section in which an MFD changes such that a difference between a maximum value and a minimum value is 0.3 ?m or more for a 100 ?m-length. A splicing loss of the HNLF and the SMF at 1,550 nm is one-fifth or less than an ideal butting loss at stationary portions thereof. A total length of the MFD transition portion is 10 mm or less. In a region between one end surface of the HNLF at the fusion point and the other end surface separated from the one end surface by 50 ?m or more and 300 ?m or less, the MFD increases monotonically from the other end surface to the one end surface.

Abstract: An optical fiber according to an embodiment includes a core and a cladding. The average value n1_ave of the refractive index of the core, the minimum value nc_min of the refractive index of the cladding, and the refractive index n0 of pure silica glass satisfy relationships of n1_ave>nc_min and nc_min<n0. The cladding contains fluorine. The fluorine concentration in the cladding is adjusted to be minimum in the outermost portion of the cladding including the outer peripheral surface of the cladding.

Abstract: An optical fiber according to an embodiment includes a core, a cladding, and a coating layer. At the boundary between the core and the cladding, the local sound velocity decreases in the direction from the core side toward the cladding side. At least in the cladding, the local sound velocity changes continuously in a radial direction. Further, the line width of the Brillouin gain of the light beam guided by the fundamental mode is 60 MHz or more.

Abstract: An optical fiber is made of silica-based glass and includes a core, a first cladding that surrounds the core and that has a refractive index lower than a refractive index of the core; and a second cladding that surrounds the first cladding and that has a refractive index lower than the refractive index of the core and higher than the refractive index of the first cladding. At least a part of the first cladding contains a photosensitive material whose refractive index increases by irradiation with light having a specific wavelength. A difference ?n between a refractive index of a portion of the first cladding, the portion being nearest to the core, and the refractive index of the core is in a range of 0.25% to 0.30%. The radius ra of the core is larger than 4.3 ?m and smaller than or equal to 5.0 ?m.

Abstract: An optical fiber according to an embodiment includes: a core; an inner cladding surrounding the core and having a refractive index smaller than a refractive index of the core; an outer cladding surrounding the inner cladding and having a smaller refractive index than the refractive index of the core and having a refractive index greater than the refractive index of the inner cladding, in which a ratio of a caustic radius to a MAC-value (caustic radius/MAC-value) at a bending radius of 10 mm at a wavelength of 1625 nm is 2.70 ?m or more.

Abstract: An optical fiber according to an embodiment has a structure for enabling determination of improvement in transmission loss at a preform stage. The optical fiber includes: a core containing Cl and having an average refractive index lower than a refractive index of pure silica glass; a first cladding containing F; a second cladding; and a resin coating, in which an effective area at a wavelength of 1550 nm is 135 ?m2 or more and 170 ?m2 or less, a ratio of the effective area to a cutoff wavelength ?C is 85.0 ?m or more, a bending loss of an LP01 mode at a wavelength of 1550 nm and at a bending radius of R15 mm is less than 4.9 dB per 10 turns, and the resin coating includes a primary resin layer having a Young's modulus of 0.3 MPa or less.

Abstract: The present embodiment relates to an optical fiber line or the like configured by connecting a single-mode optical fiber with a cladding containing fluorine and a large Aeff optical fiber by TEC connection, and a connection state between such two types of optical fibers is set such that a connection loss expressed in dB of a fundamental mode is equal to or less than 55% of an ideal butt loss expressed in dB at a wavelength of 1550 nm.

Abstract: The present embodiment relates to a CC-MCF capable of generating sufficient mode coupling even with bending or twisting less. The CC-MCF includes two fiber parts having cores mutually directly or indirectly connected, each fiber part having a plurality of cores in which a pair of adjacent cores has a mode-coupling coefficient of 1 (1/m) or more. Each fiber part is provided with a transition section including a fiber end face and a stationary section adjacent to the transition section. In the stationary section, the MFD of each core is substantially constant in a fiber longitudinal direction, and in the transition section, the MFD of each core is continuously expanding from the stationary section to the fiber end face.

Abstract: The present invention relates to a method and device for measuring optical nonlinearity of an optical fiber to be measured comprising a plurality of cores having mutually coupled waveguide modes. The method includes, at least, preparing a laser light source emitting laser light and a detecting unit determining an optical intensity, inputting laser light into a specific core of the optical fiber to be measured, determining the intensity of a specific wavelength component caused by optical nonlinearity among the reflective light components from the optical fiber to be measured, and determining optical nonlinearity of the optical fiber to be measured on the basis of the intensity of the specific wavelength component.

Abstract: An optical fiber according to an embodiment comprises, as a structure suitable for large capacity transmission over a long haul, a core, a cladding having an outer diameter of 80 ?m or more and 130 ?m or less, a primary coating, and a secondary coating having elasticity higher than that of the primary coating and an outer diameter of 210 ?m or less. The optical fiber having the structure as described above has an MFD of 10 ?m or more at a wavelength of 1550 nm, a cable cutoff wavelength longer than 1260 nm, and a microbending loss of 0.6 dB/km or less at a wavelength of 1550 nm.

Abstract: The present embodiment relates to an optical fiber line or the like configured by connecting a single-mode optical fiber with a cladding containing fluorine and a large Aeff optical fiber by TEC connection, and a connection state between such two types of optical fibers is set such that a connection loss expressed in dB of a fundamental mode is equal to or less than 55% of an ideal butt loss expressed in dB at a wavelength of 1550 nm.

Abstract: The present embodiment relates to an optical amplifier and the like having a structure for enabling efficient use of pumping light while avoiding complication of a device structure. In such an optical amplifier, since pumping light from a pumping light source is supplied to each core of an amplification MCF, a coupling MCF in which adjacent cores form a coupled core is arranged between the amplification MCF and the pumping light source. The pumping light source is optically connected to a specific core of the coupling MCF, and pumping light is coupled from the specific core to remaining cores except the specific core in the coupling MCF before pumping light is supplied to each core of the amplification MCF. This enables coupling of pumping light between optically connected cores between the amplification MCF and the coupling MCF.