Abstract: An optical fiber not only can suppress SBS but also can be produced easily. The optical fiber 1 comprises an optical core region 10 including the center axis and an optical cladding region 14 surrounding the optical core region 10. The optical core region 10 is composed of a first region 11, a second region 12, and a third region 13 in this order from the inside. The third region 13, which is a part of the optical core region 10, is a ring-shaped acoustic core region. The propagation mode of an acoustic wave can be localized in the third region 13.

Abstract: An optical fiber for Raman amplification amplifies a signal light with a pumping light. A chromatic dispersion at a wavelength of 1,550 nm is in a range between ?70 ps/nm/km and ?30 ps/nm/km. Raman gain efficiency with a pumping light of 1,450 nm is equal to or more than 5 (W×km)?1. Nonlinear coefficient at the wavelength of 1,550 nm is equal to or less than 5.0×10?9 W?1. Zero-dispersion wavelength is neither at a wavelength of the signal light nor at a wavelength of the pumping light. Cut-off wavelength is equal to or less than the wavelength of the pumping light.

Abstract: An optical transmission fiber is formed to include a relatively low-index, relatively thin outer cladding layer disposed underneath the protective polymer outer coating. Stray light propagating along an inner cladding layer(s) within the fiber will be refracted into the thin outer cladding (by proper selection of refractive index values). The thin dimension of the outer cladding layer allows for the stray light to “leak” into the outer coating in a controlled, gradual manner so as to minimize heating of the coating associated with the presence of stray light. The inventive fiber may also be bent to assist in the movement of stray light into the coating.

Abstract: An optical fiber and methods of processing and manufacturing an optical fiber comprising a core, a cladding and a coating covering a segment of the cladding proximate to an end of the optical fiber are presented where patterned apertures are provided in the coating such that a portion of light propagating in the cladding escapes through the patterned apertures of the coating. The patterned apertures allow non-confined light to escape from the cladding in the coating region to provide reduced absorption of the non-confined light by the coating.

Abstract: The invention relates to side-scattering light guides that generally comprise a core of transparent optically homogenous material seeded with diffuser particles. The light guide also comprises an optically transmitting sheath, having a lower refractive index than the core, surrounding and in contact with the sides of the core to prevent any light being transmitted along the core from escaping through the core's sides. In general, the diffuser particles impart only a small deviation to light rays incident upon them, and are distributed to scatter light being transmitted along the core so that at least some of the scattered light exits the sides of the core. A diffusing jacket is arranged to intercept scattered light exiting the sides of the core.

Abstract: Optical fiber having a coating surrounding and in direct contact with the silica based cladding region of the fiber, the coating having a Young's modulus of elasticity greater than 30 MPa. The optical fiber has low bend losses, especially low microbend induced losses. The optical fiber has a core surrounded by a cladding, and the cladding has a ring portion that includes holes or doped silica or both.

Abstract: A plastic optical fiber (11) has a core (12) and a clad (13). The clad (13) is composed of an outer clad (14) and an inner clad (15). The refractive index in the core (12) gradually increases as the distance from the center thereof decreases. The refractive index in the inner clad (15) is equal to the minimum value of the refractive index in the core (12), and the refractive index in the outer clad (14) is smaller than that in the inner clad (15). For the purpose of decreasing the transmission loss between the plastic optical fiber (11) and a light emission device or the light receiving device, the diameter d1 of the core (12) and the outer diameter d2 of the inner clad (15) satisfy the following conditions; 100(?m)?d1?700(?m) 200(?m)?d1?1000(?m) d1<d2.

Abstract: In a first aspect, the present invention comprises an optical filter comprising a fiber having a core and a cladding and a light-absorbing coating applied onto a portion of the fiber cladding, the coating attenuating loosely bound cladding modes. In another aspect, the invention comprises a fiber amplifier apparatus comprising fibers for delivering pump laser light and for monitoring signal light and at least one photodetector optically coupled to a monitoring fiber, wherein either an optical filter is disposed between a monitoring fiber and a photodetector or at least one of the fibers has a core and a cladding and a light-absorbing coating applied onto a portion of the fiber cladding. A method in accordance with the present invention includes providing an optical amplifier having fibers for delivering pump laser light and for monitoring signal light, and applying a light-absorbing coating onto a portion of one of said fibers.

Abstract: An optical waveguide environmental sensor is provided that is capable of detecting a target gas or liquid in the ambient environment in an advantageously short period of time. The waveguide is preferably in the form of an optical fiber having a cladding that contains a photonic band gap structure which in turn envelopes a light conducting, hollow core portion. The cladding further includes at least one elongated side opening that preferably extends the entire length of the fiber and exposes said hollow core portion to the ambient environment, which provides broad and nearly immediate access of the core portion to gases and liquids in the ambient environment, thereby minimizing sensor response time. The ambient gases or liquids filling the hollow core portion and elongated opening function as a ridge and slab, respectively, of an optical ridge waveguide that effectively supports at least one bound optical mode.

Abstract: Apparatus for providing optical radiation, which apparatus comprises an optical fibre (5) having a core (3), a first cladding (1) and a second cladding (2), in which the first cladding (1) has a substantially constant diameter (9) in its cross-section. The first cladding (1) can be non-circular. Advantages include more reliable cleaving, joining and splicing.

Abstract: A clad pipe (70) is produced by heating PVDF to 180° C., and then this PVDF being extruded from a melt-extrusion device. The clad pipe (70) has a square cross-section whose sides L1 are 20 mm length, and in a center thereof, there is a square hole. In the square hole, a core (72) mainly includes PMMA is formed. Accordingly, a preform (12) having a clad (71) of PVDF and the core (72) of PMMA is obtained. The preform (12) is heat-soften-drawn at 210° C. A drawing ratio is 1600. Finally, an optical member (14) having a 0.5 mm square cross-section is obtained.

Abstract: A silica based glass waveguide having almost the same optical characteristics as designed value and an optical module using a silica based glass waveguide having excellent optical characteristics and reduced connecting loss are provided. A silica based glass waveguide is comprising a core waveguide and a clad, a core waveguide is formed rectangular in cross section and of SiO2—TiO2 group glass on a synthetic silica glass substrate, and a clad is formed of SiO2—B2O3—P2O5 group glass or etc. on a synthetic silica glass substrate and a core waveguide. A synthetic silica glass substrate is formed of pure SiO2 and having birefringence quantity less than 10 nm/cm.

Abstract: A cladding is provided at an outer periphery of a solid-core doped with rare earth ions, and a metal layer is formed to be adjacent to the cladding to provide an optical fiber for a fiber laser device. The metal layer having an inner metal layer and an outer metal layer is disposed along an entire length of the optical fiber for a fiber laser device. An exciting light is incident to the optical fiber for a fiber laser device, and the exciting light is reflection-excited to emit a high power laser oscillation light. A monitoring current is constantly flown into the metal layer. When the disconnection of the optical fiber for a fiber laser device is detected based on the monitoring current, the energization of the optical fiber for a fiber laser device is stopped.

Abstract: An optical transmission fiber is formed to include a relatively low-index, relatively thin outer cladding layer disposed underneath the protective polymer outer coating. Stray light propagating along an inner cladding layer(s) within the fiber will be refracted into the thin outer cladding (by proper selection of refractive index values). The thin dimension of the outer cladding layer allows for the stray light to “leak” into the outer coating in a controlled, gradual manner so as to minimize heating of the coating associated with the presence of stray light. The inventive fiber may also be bent to assist in the movement of stray light into the coating.

Abstract: An optical fiber comprising: (i) a silica based passive core having a first index of refraction n1; (ii) a silica based cladding surrounding the core and having a second index of refraction n2, such that n1>n2, said cladding having at least one stress rod and at least one air hole extending longitudinally through the length of said optical fiber; and (iii) wherein said optical fiber supports a single polarization mode or poses polarization maintaining properties within the operating wavelength range.

Abstract: An end face structure of an optical fiber includes a coreless fiber fused to an emitting end face of the fiber optical fiber and a coating material disposed around at least the coreless fiber, a refractive index of the coating material being higher than a refractive index of the coreless fiber.

Abstract: An optical fiber includes a large graded index core of Ge doped silica for an increased bandwidth-length-product of over 100 MHz-km. A cladding layer of non-doped silica is formed on the core during the preform process and subsequently during drawing the preform an ultraviolet light curable polymer first coating is overlaid on the cladding layer. The first coating is sufficiently hardened to match the fracture characteristics of the silica core and cladding layer to facilitate crimp and cleave termination. The first coating is additionally provided with an index of refraction greater than the cladding layer to enable mode or energy stripping from the cladding layer. A second polymer layer may optionally be applied during draw for protection and to provide a tough outer layer of the optical fiber for the deformable features of a connector to hold onto after crimping.

Abstract: An elongated light-guiding element includes opposed incident and emission ends between which light propagates by total internal reflection. The light-guiding element includes a glass core with first and second glass core ends and a glass-core outer surface. A non-glass polymeric optical layer extends over at least a portion of the length of the glass core and is disposed peripherally thereabout. The optical layer has first and second optical-layer ends and an optical-layer exterior surface extending between the first and second optical-layer ends. The glass core and the polymeric optical layer exhibit indices of refraction that are matched to one another as closely as practicable such that the combination of the glass core and the optical layer exhibits optical properties similar to those that would be exhibited by an optical element of similar shape and dimensions fabricated from a single, continuous mass of optical material having a refractive index equal to the that of the glass core material.

Abstract: A coated optical fiber capable of transmitting high-power light, which is an optical fiber having an outer surface coated with a coating material, is characterized in that the coating material is made of a transparent UV curable resin so as to prevent the coating material from absorbing light leaked outside from the optical fiber to generate heat. Further, a light transmitting method is characterized in that a fiber fuse propagation threshold which is a minimal light output required for fiber fuse propagation is obtained and a transmitted light output is controlled so that the transmitted light output becomes smaller than the fiber fuse propagation threshold.

Abstract: A fiber optic conduit for use in a hostile environment includes an axial tube. The axial tube comprises a corrosion resistant material and is operable to receive one or more optical fibers. The fiber optic conduit further includes a hydrogen barrier shell that is disposed in contact with the axial tube. The hydrogen barrier shell comprises a material that is capable of reducing hydrogen permeation through the fiber optic conduit and has a thickness of at least approximately one-thousandth of an inch.

Abstract: A method and apparatus is described that use an index-of-refraction profile having a significant central dip in refractive index (or another tailored index profile) within the core of a gain fiber or a gain waveguide on a substrate. The benefits of this central dip (more power with a given mode structure) are apparent when an input beam is akin to that of a Gaussian mode. In some embodiments, the invention provides a fiber or a substrate waveguide having an index profile with a central dip, but wherein the device has no doping. Some embodiments use a central dip surrounded by a higher-index ring in the index of refraction of the core of the fiber, while other embodiments use a trench between an intermediate-index central core portion and the ring, or use a plurality of rings and/or trenches. Some embodiments use an absorber in at least one core ring.

Abstract: An assembly senses fluid pressure variations within a passageway along a length of a flowline. A fiber optic cable is disposed axially within the passageway of the flowline. The fiber optic cable experiences a mechanical strain responsive to variations in the fluid pressure of the fluid communicating through the passageway of the flowline along the length of the flowline. The assembly also includes an enhancing layer surrounding the fiber optic cable. The enhancing layer is more responsive to the fluid pressure of the fluid communicating through the passageway of the cable than the fiber optic cable, which enhances the responsiveness of the fiber optic cable to the pressure by magnifying the mechanical strain associated with the fiber optic cable within a particular region of varying fluid pressure. Strain associated with the cable is communicated through back-reflected light.

Abstract: A fiber optic cable having at least one optical fiber such as a microstructured bend performance optical fiber disposed within a protective covering. The protective covering is highly flexible and the fiber optic cable has extremely low delta attenuation when aggressively bent compared with the conventional fiber optic cable designs. By way of example, the delta attenuation of one fiber optic cable design is about 0.33 dB or less when wrapped 3 turns about a 7.5 millimeter mandrel at a reference wavelength of 1625 nanometers. Other variations of the present invention include a connector attached to the fiber optic cable.

Abstract: This invention discloses an optical fiber structured to measure stress. The optical fiber includes a core, substantially surrounding the core is a cladding having a plurality of air holes, substantially surrounding the cladding is a buffer, and substantially surrounding the buffer is a jacket.

Abstract: An optical fiber which, at an optical fiber connecting end having a plurality of voids around the periphery of a core, has a light-permeable substance, such as a resin or glass whose refractive index is lower than that of quartz type substances, filled in the voids adjacent to the connecting end. An optical fiber connecting section where an optical fiber having a plurality of voids in a clad around the periphery of a core is connected to another optical fiber, wherein the optical fiber is connected end-to-end to aforesaid another optical fiber through a refractive index matching agent whose refractive index at the minimum temperature in actual use is lower than that of the core.

Abstract: A high-voltage component, having a first end and a second end, whereby the first end is on a high-voltage potential with respect to the second end. An insulating part, is arranged between the first end and the second end, and an optical fiber is integrated in the high-voltage component and extends from the first end to the second end. A capillary extends from the first end to the second end and is arranged within the insulating part. The inside diameter of the capillary exceeds the outside diameter of the fiber, and the fiber is arranged within the capillary. The capillary includes a protective medium to achieve a dielectric strength in the capillary, which dielectric strength is suitable for the operating conditions.

Abstract: An optical fiber cable has a highly reduced diameter. The cable has a central strength member; a number of tubes containing loosely arranged optical fibers, each tube having a thickness, and each optical fiber having a coating; and a protective outer jacket, wherein the filling coefficient of optical fibers in at least one loose tube is ?45°/0. The tubes are made of a material having an elasticity modulus ?700 MPa; and the optical fibers are SM-R fibers having a microbending sensitivity ?4.0 dB·km?1/g·mm?1 at a temperature of about ?30° C. to +60° C. at about 1550 nm.

Abstract: In a glass optical waveguide having a core containing at least one oxide selected from the group of glass-constituting oxides consisting of Bi2O3, Sb2O3, PbO, SnO2 and TeO2, large transmission loss of light which occurs when the cross-sectional shape of the core is rectangle, is reduced, and wherein the glass optical waveguide contains at least total 35% in mass % of at least one type of the above glass-constituting oxides, wherein the cross-sectional shape of the core is trapezoidal, among two parallel sides of the trapezoid, a long side is in a substrate side and among four sides constituting the trapezoid, angles of two oblique sides to the long side are each within a range of from 60 to 80°.

Abstract: Apparatus and method are provided for transmitting at least one electro-magnetic radiation is provided. In particular, at least one optical fiber having at least one end extending along a first axis may be provided. Further, a light transmissive optical arrangement may be provided in optical cooperation with the optical fiber. The optical arrangement may have a first surface having a portion that is perpendicular to a second axis, and a second surface which includes a curved portion. The first axis can be provided at a particular angle that is more than 0° and less than 90° with respect to the second axis.

Abstract: A guide hole guides a primary-coated optical fiber to a tubular inlet hole. An inner diameter of the guide hole is larger than that of the tubular inlet hole. An inner diameter of the tubular inlet hole is in a range from 1.5 times to 2.0 times that of the primary-coated optical fiber. A length of the tubular inlet hole is in a range from 1.0 mm to 2.0 mm. A depth of the guide hole is in a range from 2.0 mm 9.0 mm. A relation B?A is satisfied, with B equal to or larger than 7.0 mm, where A is an inner diameter of a leading edge of the guide hole continued to a trailing edge of the tubular inlet hole, and B is an inner diameter of a trailing edge of the guide hole.

Abstract: This invention relates to an optical fiber for long period grating (LPG), LPG components, and manufacturing method of LPG used as a mode coupler, an optical filter, etc. The optical fiber for LPG comprises a core layer, a first cladding layer that surrounds said core layer and transmits the cladding modes, and a second cladding layer that surrounds said first cladding layer and confines the optical signal of the cladding mode within said first cladding layer. The LPG component comprises an optical fiber for LPG, a coating reinforcement to cover and reinforce said optical fiber for LPG. The manufacturing method of LPG comprises a step of preparation of an optical fiber, a step of constructing the LPG on a predetermined region in said core of said optical fiber by irradiating laser light on said region over a predetermined period corresponding to the LPG, on the predetermined part of said optical fiber, and a step which covers and reinforces said grating region.

Abstract: An optical fiber comprises core and cladding regions configured to guide the propagation of light (or radiation) in the core region. The cladding region includes a periodic structure configured to produce light guiding by bandgap confinement. In order to suppress higher order odes (HOMs) in the core region, the cladding region includes at least one perturbation region configured so that a mode of the cladding region is resonant with a HOM of the core region. In a preferred embodiment of my invention, the perturbation region is configured so that the fundamental mode of the cladding region is resonant with a HOM of the core region.

Abstract: An optical fiber including: (i) a silica based, Yb doped core having a first index of refraction n1, said core comprising more than 1 wt % of Yb, said core having less than 5 dB/km loss at a wavelength situated between 1150 nm and 1350 nm and less than 20 dB/km loss at the wavelength of 1380 nm and slope efficiency of over 0.8; and (ii) at least one silica based cladding surrounding the core and having a second index of refraction n2, such that n1>n2.

Abstract: The present invention provides a communication cable buffer tube having a flexural modulus ranging from about 180 kpsi to about 280 kpsi.

Abstract: An optical fiber includes a glass fiber having a glass core and a cladding that contains voids that are spaced apart from the core, in contact with the core, or form a substantial portion of the core. The voids act as trapping sites for ingressing molecules from the surrounding environment, thereby reducing the effect of such molecules on the fiber's light-transmission properties.

Abstract: An apparatus including a microchannel plate having a structure that defines multiple microchannels. The structure includes multiple claddings that form the walls of the microchannels, each of the claddings including a semiconducting layer. The claddings are surrounded by a glass having a lower percentage of materials having atomic numbers higher than 34 as compared to the cladding. The glass has a higher percentage of neutron absorbing material than the cladding, the neutron absorbing material capable of capturing neutrons in reactions that result in secondary electron emissions in the microchannels.

Abstract: An optical fiber made of quartz or glass and having a core and a cladding includes a microporous silica solution applied to an outer peripheral surface thereof, which is synthesized from a mixture of silicon alcoxide, active alcohol for facilitating hydrolytic action, alcohol, and water, by means of the sol-gel process, followed by baking to form a thin film of microporous silica made chiefly of silicon. Microporous of the thin film of microporous silica have function of cushioning to cushion and restrain that micro cracks much existing in the cladding undergo growth when the optical fiber is bent so that the optical fiber is likely to be broken. And the thin film of microporous silica which made chiefly of silicon has high heat-resistant properties similarly to the optical fiber itself. Accordingly, a heat-resistant optical fiber very excellent in heat-resistant properties is provided.

Abstract: An optical fiber having an internal glass portion, a first coating layer surrounding the glass portion and a second coating layer surrounding the first coating layer. The first coating layer is formed from a cured polymeric material obtained by curing a radiation curable composition having a radiation curable oligomer having a backbone derived from polypropylene glycol and a dimer acid based polyester polyol. The cured polymeric material has: (a) a hardening temperature (Th) from ?10° C. to about ?20° C. and a modulus measured at the Th lower than 5.0 MPa; or (b) a hardening temperature (Th) from ?20° C. to about ?30° C. and a modulus measured at the Th lower than 20.0 MPa; or (c) a hardening temperature (Th) lower than about ?30° C. and a modulus measured at the Th lower than 70.0 MPa.

Abstract: Provided is a method of manufacturing an optical fiber preform from which an optical fiber having the desired characteristics can easily be produced.

Abstract: In general, in one aspect, the invention features a waveguide that includes a core extending along a waveguide axis and a confinement region surrounding the core. The confinement region includes a spiral portion and a non-spiral portion, wherein the spiral portion and the non-spiral portion extend along the waveguide axis.

Abstract: The invention relates to the field of components with optical fibers and of associated optical fibers. The invention relates, on the one hand, to a component with optical fiber including an at least partly bent optical fiber (2) which successively comprises, from the center to the periphery, an optical core (10) based on silica, an optical cladding (11) based on silica, and a coating (12) having a transparency to infrared radiation larger than 85%. On the other hand, the invention relates to an optical fiber successively comprising, from the center to the periphery, an optical core (10) based on silica, an optical cladding (11) based on silica, and a coating (12) having a transparency to infrared radiation larger than 85%.

Abstract: Novel preforms and methods of making novel preforms are described. The preforms are suitable for being drawn into photonic bandgap optical fibres. In one form, the preform comprises a stack of elongate members having, in transverse cross section, a triangular close-packed arrangement of circular cross section capillaries, which define interstitial regions containing solid rods. The stack is supported around a relatively large capillary, which defines an inner region of the stack. The stack may be adapted by varying the number of rods in any given interstitial region, in order to generate various different configurations of cladding structure, which can be made into optical fibres having surprising operational characteristics, such as a split gap.

Abstract: A method of measuring polarization mode dispersion (PMD) of an optical fiber, includes estimating PMD when an optical fiber is formed as an optical cable, from a beat length when the optical fiber is wound around a bobbin, and an average coupling length when the optical fiber is formed as the optical cable.

Abstract: The invention provides techniques for drawing fibers that include conducting, semiconducting, and insulating materials in intimate contact and prescribed geometries. The resulting fiber exhibits engineered electrical and optical functionalities along extended fiber lengths. The invention provides corresponding processes for producing such fibers, including assembling a fiber preform of a plurality of distinct materials, e.g., of conducting, semiconducting, and insulating materials, and drawing the preform into a fiber.

Abstract: An upcoated optical fiber includes an optical fiber having a ultra-violet (UV) curable upcoating and a slip layer disposed between the optical fiber and the upcoating. The upcoating is mechanically strippable from the optical fiber and may be colored for identification of the optical fiber. In one embodiment, the slip layer and upcoating both have predetermined glass transition temperatures that are within about 15° C. of each other for improving mechanical characteristics. The slip layer may be essentially the same color as the upcoating for identification of the optical fiber after the upcoating is removed or it may be uncolored. In suitable embodiments, the slip layer may include a micronized poly-tetra-fluoro-ethylene (PTFE), a silicone, and/or a dispersing agent for enhancing the strip performance of the upcoating over a range of temperatures.

Abstract: In traveling-wave ring-resonator an optically nonlinear crystal for converting visible radiation to ultraviolet (UV) radiation has an input face and two output faces. The visible light propagates through the crystal from the input face to one of the output faces. That output face is coated with a dichroic optical coating that transmits unconverted visible light and reflects the ultraviolet light. The reflected ultraviolet light exits the optically nonlinear crystal via the other output face and is coupled out of the resonator at an angle to the resonator axis.

Abstract: A photonic crystal fiber includes a core region for propagating light in a longitudinal direction of the fiber, a cladding region surrounding the core region, the cladding region including micro-structural elements extending in the longitudinal direction. The cladding region further includes at least one stress element having a coefficient of thermal expansion ?T,SAP and extending in the longitudinal direction of the photonic crystal fiber, the stress element(s) being located in a cladding background material having a coefficient of thermal expansion ?T,cladback different from ?T,SAP. The location of the at least one stress element relative to the core region and the micro-structural elements and the coefficients of thermal expansion ?T,SAP and ?T,cladback are adapted to provide a stress induced birefringence in the core region of the photonic crystal fiber. An article includes a photonic crystal fiber, a method of manufacturing and the use of a photonic crystal fiber are furthermore provided.

Abstract: An optical fiber ribbon includes a plurality of optical fibers encapsulated within a matrix material, where the optical fiber coating(s) and the matrix material(s), and optionally any ink layers thereon, are characterized by compatible chemical and/or physical properties, whereby the fiber coating and matrix and any ink layers therebetween can be reliably stripped from the optical fibers to afford a suitable strip cleanliness. Novel ink formulations that can be used in the making of such fiber optic ribbons, methods of making such ribbons, and their use are also described.

Abstract: An optical fiber tape core comprises an optical fiber core assembly and a coating layer formed of silicone rubber and arranged on at least one side of the optical fiber core assembly. In the optical fiber core assembly, plural optical fiber cores two-dimensionally are arranged in parallel with each other. The silicone rubber which forms the coating layer has a hardness of from 20 to 90 and a tensile strength of from 15 to 80 kgf/cm2.

Abstract: The present invention relates to an optical fiber which has a structure for further increasing an FOM (=|dispersion|/loss) and which can be applied to a dispersion compensation module. The optical fiber is mainly composed of silica glass and has a core region including a center of an optical axis, a depressed region surrounding the core region, a ring region surrounding the depressed region, and a cladding region surrounding the ring region and doped with F. As compared with the refractive index of pure silica glass, a relative refractive index difference of the core region is 3% or more but 4% or less, a relative refractive index difference of the depressed region is ?1% or more but ?0.5% or less, a relative refractive index difference of the ring region is 0.01% or more but 0.24% or less, and a relative refractive index difference of the cladding region is ?0.3% or more but ?0.1% or less. The FOM at the wavelength of 1550 nm is 250 ps/nm/dB or more.