Abstract: An optical transmission system is provided. The system includes a series of consecutive blocks of optical fiber. Each block of the system includes a first, second and third series of spans of optical fiber, where the second series of spans compensates for accumulated dispersion in the first and third series in the wavelength range of transmission. Optionally either the first or third series can be omitted.

Abstract: Disclosed is a single mode waveguide fiber and a method of making a single mode or multimode waveguide fiber which has an azimuthally and radially asymmetric core. This asymmetry provides additional degrees of freedom for use in forming a waveguide having particular performance characteristics.

Abstract: The specification describes an improved optical fiber design in which the criteria for high performance in a Raman amplified optical system, such as moderate effective area, moderate dispersion, low dispersion slope, and selected zero dispersion wavelength, are simultaneously optimized. In preferred embodiments of the invention, the dispersion characteristics are deliberately made selectively dependent on the core radius. This allows manufacturing variability in the dispersion properties, introduced in the core-making process, to be mitigated during subsequent processing steps.

Abstract: An optical module for optically coupling an input side and an output side with each other through an optically functional portion inserted between the input side and the output side. At least one of the input side and the output side includes a plurality of collimators. At least one of the collimators is made different from the other collimators in at least one of the distance between the focal point of a corresponding lens and a corresponding light exit or incident surface, the numerical aperture of the light exit or incident surface, the effective focal length of the lens, the wavelength used and the distance between optical axes of adjacent ones of the collimators so that the size and position of a beam waist on an input side are made substantially coincident with those on an output side.

Abstract: A dispersion compensating fiber and module are described for controlling residual dispersion in a dispersion compensated system. The dispersion compensating fiber is designed with dispersion curve having an inflection point at a wavelength near the optical transmission operating wavelength region. The dispersion curve, having an inflection point near the operating wavelength region, produces a relative dispersion slope that closely matches the relative dispersion slope of the transmission fiber over a relatively wide bandwidth surrounding the operating wavelength region.

Abstract: Systems and methods are described for fabricating a varying-waveguide optical fiber. In one described method, a preform is fabricated having a core and at least one cladding region. The cladding region has a higher viscosity and the core region has a lower viscosity. The relative viscosities of the cladding region and core are chosen such that, when tension is applied to an optical fiber drawn from the preform, the applied tension is primarily borne by the cladding region thereby causing a viscoelastic strain to be frozen into the cladding region, while creating a minimal viscoelastic strain in the core. The method further includes drawing the preform into an optical fiber under an applied tension, such that a viscoelastic strain is frozen into the cladding region the frozen-in viscoelastic strain decreasing the cladding region refractive index.

Abstract: An optical fiber is described in which a core is surrounded by a cladding having a refractive index that varies periodically in the angular sense around the core. By appropriate design of the cladding it is possible to provide an optical fiber capable of single-mode operation over a wide range of wavelengths with a large effective area.

Abstract: A method of using a beam of ultra-short laser pulses, having pulse durations below 10 picoseconds, to adjust an optical characteristic within an optical medium is provided. The beams would have an intensity above a threshold for altering the index of refraction of a portion of the optical medium. The beams could be selectively applied to the optical medium and any structures formed or existing therein. Thus, the beam could be moved within a waveguide in the optical medium to alter the index of refraction of the waveguide forming any number of different longitudinal index of refraction profiles. The beam could also be moved within the optical medium near the waveguide to alter an effective index of refraction of a signal traveling within the waveguide. The techniques described can be used to improve, alter or correct performance of waveguide-based optical devices, such as arrayed waveguide gratings and cascaded planar waveguide interferometers.

Abstract: The present invention provides an optical fiber forming an optical transmission line for wavelength division multiplexing transmission in a 1.5 &mgr;m wavelength band, for example. The cutoff wavelength is set in the range of 1.3 &mgr;m or more to 1.4 &mgr;m or less, and the chromatic dispersion value at a wavelength of 1.55 &mgr;m is set to 4 to 10 ps/nm/km. The effective core area in at least a setup wavelength band of the 1.5 &mgr;m wavelength band is set to 40 &mgr;m2 to 60 &mgr;m2, and the dispersion slope in the 1.55 &mgr;m wavelength band is set to a positive value below 0.035 ps/nm2/km. The zero dispersion wavelength is set to 1.43 &mgr;m or less, and the bending loss at the diameter of 20 mm in the 1.5 &mgr;m wavelength band is set to 5 dB/m or less.

Abstract: An optical cable, which is flame-retardant, and has excellent adhesion of the protective covering to the fiber cladding and uniform thickness of the fiber cladding, contains a polymer optical conductor containing a fiber core; a single-layer or multi-layer fiber cladding; an inner external layer which adheres to the fiber cladding with a peel force of at least 50 N; and an outer external layer which adheres to the inner external layer with a peel force of not more than 30 N. The inner external layer contains a molding composition having a first polyamide selected from a) PA 11, b) PA 12, c) PA 1012, d) PA 1212, e) a copolyamide of at least two of PA 11, PA 12, PA 1012 and PA 1212, said copolyamide containing not more than 30 mol % of a comonomer, and f) mixtures thereof. The first polyamide contains at least 50 &mgr;eq/g of amino end groups. The first molding composition has a zero-shear viscosity of from 400 to 6000 Pas.

Abstract: Disclosed is a nonlinear dispersion-shifted optical fiber, wherein a charomatic dispersion at a wavelength of 1550 nm is equal to a set value required for optical signal processing utilizing a nonlinear phenomenon, a dispersion slope at a wavelength of 1550 nm falls within a range of 0.001 to 0.1 ps/nm2/km, a margin of fluctuation of the charomatic dispersion in a longitudinal direction of the optical fiber at a wavelength of 1550 nm falls within a range of 0.01 to 3 ps/nm/km, and a nonlinear constant n2/Aeff at a wavelength of 1550 nm is not smaller than 15×10−10/W.

Abstract: A low-dispersion optical fiber provides both reduced chromatic dispersion in a used wavelength band and increased effective core area. The low-dispersion optical fiber is made by covering a center core (1) with a first side core (2), covering the first side core (2) with a second side core (3), and covering the second side core (3) with a cladding (5). When the maximum refractive index of the center core (1) is written n1, the minimum refractive index of the first side core (2) is written n2, the maximum refractive index of the second side core (3) is written n3 and the refractive index of the cladding (5) is written nc, then n1>n3>nc>n2 is satisfied. Relative refractive index differences &Dgr;1, &Dgr;2 and &Dgr;3 with respect to the cladding (5) of the maximum refractive index of the center core (1), the minimum refractive index of the first side core (2) and the maximum refractive index of the second side core (3) respectively are made 0.4%≦&Dgr;1≦0.7%, −0.30%≦&Dgr;2≦−0.

Abstract: A mode transformer (10) includes a passive waveguide (120) having a first composition co-existing with a second composition to provide a guided optical wave (250). A p-doped re-growth layer (130) having the first composition is disposed on top of the passive waveguide (120). A compensated n-doped buffer (110) is disposed underneath the passive waveguide (120). The compensated n-doped buffer (110) has the first composition and a sufficient concentration of a third composition such that the compensated n-doped buffer layer has a reduced index difference between the p-doped re-growth layer (130) and the compensated n-doped buffer layer (110) to compensate the index difference between the p-doped re-growth layer (130) and the originally un-compensated n-doped buffer in order to preserve the symmetry of the guided optical wave (250).

Abstract: An optical fiber with lens for constituting an optical functional component capable of light beam propagation, which improves the stability in holding and handling and contributes to downsizing. To one end of a single mode (SM) optical fiber, which is a main part of the optical fiber with lens, a graded index (GI) optical fiber functioning as a convergence type rod lens and having a predetermined length is integrally connected, and this GI optical fiber is thinner than SM optical fiber. The refractive index distribution constant {square root}A of the GI optical fiber is from 1.0 to 4.0, and the end surface thereof is inclined at from 2.0 degrees to 4.0 degrees. Further, the GI optical fiber may be constituted only by a core part without a clad part.

Abstract: A fiber lens includes a graded-index lens, a single-mode fiber disposed at a first end of the graded-index lens, and a refractive lens having a hyperbolic or near-hyperbolic shape disposed at a second end of the graded-index lens to focus a beam from the single-mode fiber to a diffraction-limited spot.

Abstract: A gap-soliton structure is provided. The gap-soliton structure includes a cladding structure having alternating layers of different index values. A core region is interposed between the alternating layers of index values. The core or the cladding structure includes one or more nonlinear materials so as to achieve gap-soliton bistability.

Abstract: Disclosed is a single mode optical waveguide fiber designed for use in high performance telecommunication systems. The novel core profile design improves bending performance to provide enhanced resistance to adverse environments. Total dispersion over an extended wavelength window is maintained low by placing the zero dispersion wavelength above the upper limit of the operating window. In addition, cut off wavelength is increased to just below the operating window. Ease of manufacture is retained as is very low waveguide attenuation.

Abstract: An optical fiber is described in which the cladding is provided with a refractive index that increases in a radially outward direction. In particular embodiments the refractive index of the cladding increases monotonically from a low value to a value close to or higher Than the refractive index of the core.

Abstract: A plastic optical fiber which is a graded index optical fiber having a concentric inner/outer at least two layer structure, wherein the inner layer has a graded index structure made of a non-crystalline fluoropolymer (a) having substantially no C—H bond, and the outer layer has a refractive index lower than the refractive index of the outermost portion of the inner layer and is made of a fluoropolymer material (c) selected from the following 1) and 2): 1) a fluoropolymer (d) containing the same polymerized units as the polymerized units in the fluoropolymer (a), and 2) a mixture (f) of a fluoropolymer (a) with another fluoropolymer (e).

Abstract: The instant invention concerns optical fibers that have complex-valued Vc-parameters due to gain g established by active dopants that are doped into the fiber core in accordance with a doping profile. In particular, the doping levels are very high, such that the gain g makes a sufficiently large contribution to an imaginary part of the complex-valued Vc-parameter to define at least one gain-guided mode, e.g., the fundamental mode or several low-order modes of radiation in the optical fiber. The fiber does not require any index-guiding effects to a single mode or just a few of the lowest-order modes in large cross-section cores having diameters in the range from 50 &mgr;m to 500 &mgr;m in diameter and yield kilowatt level output power. The fiber may, in addition to gain-guiding, take advantage of a refractive index profile to provide for index-guiding or index-antiguiding effects in addition to gain-guiding.

Abstract: An optical attenuator which provides almost the same degree of attenuation even when the difference in wavelength of two different kinds of input optical signals is small. Another optical attenuator is provided with a dopant concentration in a technically realizable range which increases the difference in optical attenuation of two different kinds of input optical signals. Almost the same degree of attenuation may be obtained even when the difference between wavelengths is small by canceling the wavelength dependency of attenuation of the dopant by raising the refractive index of an axially central portion of the core as compared to that of the peripheral portion of the core and by taking into account the type and area of the dopant and the ratio of the difference &Dgr;2 between the refractive indexes of the cladding and the axial portion of the core and the difference &Dgr;1 between the refractive index of the cladding and the refractive index of the peripheral portion, i.e., &Dgr;1/&Dgr;2.

Abstract: Coating for an optical fiber and method of manufacturing thereof, the coating comprising at least one partly crosslinked polymer having a level of crosslinking which increases according to a radial distance as one moves from the internal surface (3) of the coating (4) which interfaces with a cladding section (2) to the external surface of the coating (4). The coating comprises a single resin which is composed of a volatile, multifunctional and moderately reactive monomer dissolved in a fast curable oligomer, having a low modulus when polymerized.

Abstract: A thermally-shaped optical fiber and a method for forming the same so as to minimize the presence of optical artifacts in the optical fiber that contributes to insertion loss.

Abstract: A method of forming a holey waveguide, the method comprising the steps of forming a guiding region of a preform, forming a cladding region of the preform, wherein at least a portion of the cladding region of the preform is formed from a plurality of cladding tubes of at least two different diameters, choosing at least one of the diameters of the cladding tubes in a manner such as to reduce a total number of cladding tubes required to build up said portion of the cladding region when compared with utilising cladding tubes of the same diameter for said portion, and drawing the waveguide from the preform.

Abstract: The energy beam guide comprises a first region having a first refractive index, the first region having an energy beam receiving end and an inclined first boundary opposing the energy beam receiving end. The energy beam guide also includes a second region having a second refractive index that is less than the first refractive index. The second region shares the first boundary with the first region, and has a declined second boundary opposing the first boundary. A predetermined distance separates the first and second boundaries. Finally, the energy beam guide comprises a third region having a third refractive index. The third region shares the second boundary with the second region. Also provided are a method for making and using the energy beam guide.

Abstract: The present invention aims to provide a dispersion compensator which is ultra small in size and low in cost and capable of controlling dispersion compensating values, and an optical transmission system using the dispersion compensator. A dispersion property of light that propagates through defects in a photonic crystal, is used to compensate for each wavelength dispersion. A dispersion compensator comprises a dispersion-compensating-waveguide array in which a plurality of dispersion compensating waveguides having dispersion compensating values different from one another are placed, a drive unit for driving the dispersion-compensating-waveguide array, and optical fibers for inputting/outputting a light signal. Each of the dispersion compensating waveguides comprises regular waveguides and a waveguide made of defects in photonic crystal. The lengths of the waveguides made of the defects in photonic crystal are changed one by one to make dispersion compensating values different from one another.

Abstract: An optical fiber comprises a core region, an inner cladding region, and an outer cladding region. Each of the core region and inner cladding region is doped with GeO2, whereas the inner cladding region is also doped with F element. The core region has a refractive index higher than each of the refractive index of the inner cladding region and the refractive index of the outer cladding region. Each of the core region and inner cladding region doped with GeO2 has a UV photosensitivity. The deviation in concentration distribution of GeO2 added to the inner cladding region is so small that the deviation in UV photosensitivity in the inner cladding region is ±10% or less.

Abstract: An optical element comprising an elongated channel for light travel comprising a light transmitting polymeric central core and further comprising multilayer particles, wherein a majority of the particles have both a longest dimension less than 1 micrometer and an aspect ratio of longest to smallest dimension of from 1000:1, to 10:1, wherein the particles are arranged in a concentration differential in at least a portion of a plane normal to the length of the channel so as to create a refractive index gradient in that plane.

Abstract: An optical waveguide designed to generate positive dispersion when operated in a high order mode. The optical waveguide in one embodiment is designed to generate positive dispersion slope, in another embodiment to generate negative dispersion slope and in yet another embodiment nominally zero dispersion slope. In one embodiment the high order mode is the LP02 mode and in another embodiment the high order mode is the LP03 mode. In another embodiment the optical waveguide is a few mode fiber. In an exemplary embodiment the optical waveguide is used in combination with a mode transformer, such as a transverse mode transformer to achieve the desired high order mode.

Abstract: A miniaturized lens array for unity magnification imaging comprises a plurality of rod lenses arranged in one row. An arrangement pitch D of the rod lenses is defined to satisfy (2 m+1)·D≦2.1 mm or 2.5 mm. An angle of aperture &thgr; of the rod lens is defined to satisfy &agr;D/6×{n·cos−1(−&agr;/2/m)+(4 m2/&agr;2−1)1/2}≦&thgr;≦&agr;D/2×(4/m2/&agr;2−1)1/2. The arrangement pitch D and angle of aperture &thgr; are defined in this manner, and it is therefore possible to obtain the lens array whose difference between a total width and effective lens width is equal to or smaller than 2.1 mm or 2.5 mm.

Abstract: An optical element comprising an elongated channel for light travel comprising a light transmitting polymeric central core and further comprising multilayer particles, wherein a majority of the particles have both a longest dimension less than 1 micrometer and an aspect ratio of longest to smallest dimension of from 1000:1, to 10:1, wherein the particles are arranged in a concentration differential in at least a portion of a plane normal to the length of the channel so as to create a refractive index gradient in that plane.

Abstract: An optical fiber transmission line including first, second and third optical fibers connected together so that light travels through the transmission line from the first optical fiber, then through the second optical fiber and then through the third optical fiber. The first, second and third optical fibers have first, second and third characteristic values, respectively. The second characteristic value is larger than the first characteristic value and the third characteristic value. The characteristic value of a respective optical fiber being a nonlinear refractive index of the optical fiber divided by an effective cross section of the optical fiber. Pump light is supplied to the transmission line so that Raman amplification occurs in the transmission line as an optical signal travels through the transmission line.

Abstract: An optical element comprising an elongated channel for light travel comprising a light transmitting polymeric central core and further comprising multilayer particles, wherein a majority of the particles have both a longest dimension less than 1 micrometer and an aspect ratio of longest to smallest dimension of from 1000:1, to 10:1, wherein the particles are arranged in a concentration differential in at least a portion of a plane normal to the length of the channel so as to create a refractive index gradient in that plane.

Abstract: Methods and apparatus for producing an optical waveguide illuminator are disclosed. By controlling the propagation of light in the core and cladding regions of the waveguide, distributed light emission along a length of an optical fiber or along a planar waveguide surface can be achieved by varying the core/cladding refractive index ratio and introducing light scattering centers in the core.

Abstract: The present invention relates to a dispersion compensating optical fiber (“DC fiber”) having a segmented core and having a negative total dispersion and negative dispersion slope in the C-band. The index profile of the fiber is selected to provide an optical properties suitable for a high performance communication system operating in the C-band wavelength band, i.e., between about 1525 nm to 1565 nm. The DC fiber according to the invention exhibits dispersion slope at 1549 nm more negative than −3.4 ps/nM2-km and has a negative &Dgr;2% that is more negative than −0.4%. Preferably, the DC fiber has a total dispersion more negative than −125 ps/nm2-km. The DC fiber may be optically connected to a Non-Zero Dispersion Shifted Fiber (NZDSF) in the system to compensate for dispersion thereof. Optionally, the transmission system may include a positive dispersion, positive slope trim fiber.

Abstract: A dispersion control fiber and a method of manufacturing a large size preform are provided. In one embodiment, the dispersion control fiber comprises a core composed of SiO2, GeO2, P2O5 and Freon, and a cladding composed of SiO2, GeO2, P2O5, and Freon. The P2O5 content is selected not to exceed 10% of the total weight of a compound composing the core. An embodiment of the method of manufacturing a large size preform for a dispersion control fiber by an MCVD process comprises depositing SiO2, GeO2, P2O5, and Freon in an inner periphery of a deposition tube to form a cladding layer, and depositing SiO2, GeO2, P2O5 and Freon on an inner periphery of the cladding layer to form a core layer.

Abstract: An optical signal transmission link includes a first single mode optical fiber for receiving an optical signal, and a graded index multimode optical fiber for receiving the optical signal from the first single mode optical fiber. The multimode fiber of the transmission link is adapted to support the propagation of greater than or equal to 4 LP modes within the wavelength range of from about 1310 nm to about 1550 nm, has a mode field diameter of the fundamental mode of within the range of from about 3.0 &mgr;m to about 14.0 &mgr;m within the wavelength range of from about 1300 nm to about 1650 nm, and has a numerical aperture (NA) value of greater than or equal to about 0.16.

Abstract: There is provided an apparatus for fabricating an apodized fiber grating.

Abstract: A dispersion management optical transmission system obtained by connecting a positive fiber having a positive dispersion in the 1.5 &mgr;m band and a negative fiber having a negative dispersion, suppressing dispersion in the 1.5 &mgr;m band, suppressing the occurrence of non-linear phenomena, and reducing the transmission loss and an optical transmission line using the same, wherein the dispersion of the positive fiber in the 1.55 &mgr;m band is 8 to 15 ps/nm/km and the dispersion slope is at least 0.04 ps/nm2/km, the dispersion of the negative fiber in the 1.55 &mgr;m band is not more than −40 ps/nm/km and the dispersion slope is not more than −0.08 ps/nm2/km, the cumulative dispersion of the positive fiber is at least 200 ps/nm, and the average dispersion when combining the positive fiber and the negative fiber module is suppressed to any wavelength region of the 1.5 &mgr;m band.

Abstract: An optical fiber having a good signal-to-noise ratio (SNR) and high Raman efficiency in an optical signal transmission system using Raman amplification, the optical fiber having a refractive index profile, including at least one annular region between a center core and a cladding layer, a Rayleigh scattering coefficient not more than 1 &mgr;m4·dB/km, a relative refractive index difference of the center core with respect to the cladding layer of a positive value not more than 0.9%, a relative refractive index difference of an annular region adjoining the center core with respect to the cladding layer from −0.7% to −0.

Abstract: A method of fabricating an optical waveguide structure includes the step of introducing light into a photo-curable liquid resin. The liquid resin can be a mixture of two types of photo-curable liquid resins having different curing initiation wavelengths and different refractive indexes. The method can include dipping one end of a fiber into the liquid mixture. Light having a wavelength &lgr;1 can be radiated from the tip end of the optical fiber in order to cure one of the photo-curable liquid resins thereby forming a waveguide. Light having a different wavelength &lgr;2 can be radiated from an area surrounding the waveguide so as to cure the liquid mixture and form a cladding portion around the waveguide.

Abstract: A dispersion management optical fiber transmission line of a superlow loss formed by combining a plurality of optical fibers and suitable for long distance, high speed, large capacity transmission, that is, an optical fiber transmission line including a positive dispersion optical fiber having a positive dispersion and a positive dispersion slope and a negative dispersion optical fiber having a negative dispersion and negative dispersion slope and having a non-zero dispersion at the 1.55 &mgr;m, wherein the transmission loss at the 1.55 &mgr;m band of the positive dispersion fiber and the negative dispersion fiber are both not more than 0.23 dB/km and the difference in transmission losses of the two optical fibers is not more than 0.05 dB/km.

Abstract: The present invention provides methods and optical fibers for periodically pinning an actual (random) accumulated chromatic dispersion of an optical fiber to a predicted accumulated dispersion of the fiber through relatively simple modifications of fiber-optic manufacturing methods or retrofitting of existing fibers. If the pinning occurs with sufficient frequency (at a distance less than or are equal to a correlation scale), pulse degradation resulting from random chromatic dispersion is minimized. Alternatively, pinning may occur quasi-periodically, i.e., the pinning distance is distributed between approximately zero and approximately two to three times the correlation scale.

Abstract: The optical fiber has a dispersion value at a 1.55 &mgr;m-wavelength band, of 6 to 24 ps/nm/km, and satisfies A>3×D+40, where D represents a dispersion value (ps/nm/km) at a central wavelength of a 1.55 &mgr;m-wavelength band, and A represents an effective core area (&mgr;m2). The optical transmission line for transmitting an optical signal, which includes the optical fiber is provided as well.

Abstract: A planar waveguide that has a graded index layer at the core/cladding interface to reduce scattering losses due to core/cladding interface roughness. The refractive index at the core/cladding interface is changed from that of the core to that of cladding gradually by having a graded index layer. The graded index layer reduces the scattering of light traveling in the waveguide by reducing the effect of the roughness at the abrupt interface between the core and the cladding. Using a proper design, the graded index layer also minimizes the modal and polarization dispersion of the optical mode traveling in the waveguide.

Abstract: An optical waveguide fiber including a centermost core segment surrounded by four other core segments. At a wavelength of about 1550 nm, the optical fiber exhibits an effective area of greater than about 50 &mgr;m2, a dispersion of greater than about 4 ps/nm/km, and a dispersion slope of less than about 0.03 ps/nm2/km.

Abstract: Disclosed is a single mode optical waveguide fiber having a segmented core in which the central segment is a void. The shape and radial extent of the core segments are selected to provide a low dispersion slope together with large effective area and good bend resistance. Embodiments of the refractive index profiles in accord with the invention are shown having two or three annular segments surrounding the central void. The presence of the void provides the benefits of a negative relative index located centrally in the core region without the process difficulties associated with the use of dopants that decrease the refractive index of the waveguide fiber.

Abstract: An optical fiber grating coder includes predetermined codewords imprinted into an optical fiber in the form of a plurality of striations through an apparatus including a light source, an amplitude mask, and a phase mask. A fabrication method of the optical fiber grating coder includes providing a light source, an amplitude mask designed for predetermined codewords, a phase mask, and an optical fiber; exposing the optical fiber; and forming an optical fiber grating coder into the optical fiber. A fabrication apparatus of the optical fiber grating coder includes a light source; an amplitude mask designed for predetermined codewords; a phase mask; and an optical fiber where the optical fiber grating coder is to be formed.

Abstract: A method of and an apparatus for expanding the mode field diameter of an optical fiber by heating a specified region of the optical fiber with a uniform or desired temperature distribution for forming a thermally-diffused expanded core (TEC). The mode field diameter of the optical fiber is expanded by heating an optical fiber 1 with a burner 11 so as to thermally diffuse the dopant forming the refractive-index profile. The burner 11 has a heating surface 11a in which a plurality of gas-issuing holes 12 are arranged such that a plurality of parallel rows each of which is composed of a plurality of gas-issuing holes 12 are parallel to the axis of the optical fiber 1.

Abstract: Disclosed is an optical fiber having a desired dispersion value to sufficiently suppress a non-linearity phenomenon, that is, a four-wave mixing phenomenon, occurring at a channel spacing of 50 GHz while minimizing the expense consumed for a compensation for dispersion. The optical fiber satisfies optical characteristics defined by a dispersion value of 7 to 10 ps/nm-km at a wavelength of 1,550 nm, a zero dispersion wavelength of 1,450 nm or less, and a cut-off wavelength of 1,250 nm or less. The optical fiber includes a core having a desired diameter (d1) and a desired refractive index (n1), the cladding surrounding the core and having a refractive index (ncl) less than the (n1), of the core (ncl<n1) or (n2) less than the outer cladding (n2<ncl). The (n2) of the inner cladding may also be less than the (n1) of the core and more than the (ncl) of the outer cladding.