Abstract: An optical fiber includes a core region having a first refractive index and a cladding region having a second refractive index lower than the first refractive index on an outer circumference of the core region. The cladding region includes four holes formed to have a four-fold rotational symmetry with respect to a center axis around the core region in a longitudinal direction, such that a zero-dispersion wavelength is 900 nm to 1150 nm and a cutoff wavelength is equal to or shorter than 950 nm.

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: A fiber laser includes in a resonator: a normal dispersion optical fiber; an anomalous dispersion optical fiber; a rare earth-doped optical fiber as a gain medium; and a mode locking mechanism, in which at least the rare earth-doped optical fiber is included as the normal dispersion optical fiber, and a length of the rare earth-doped optical fiber is set shorter than that of the anomalous dispersion optical fiber.

Abstract: An optical amplification fiber for an optical fiber amplifier that amplifies a signal light using a pumping light has an absorption coefficient that satisfies conditional relations ?s?2.0 dB/m and ?p/?s??0.0697×?s+1.30, where ?p is the absorption coefficient in a pumping light wavelength band, and ?s is the absorption coefficient in a signal light wavelength band.

Abstract: An optical fiber for optical amplification, characterized in that a full width at half maximum of gain spectrum is 45 nm or more; and a maximum value of power conversion efficiency is 80% or more. A method for producing a rare earth element-doped glass for use in manufacturing the optical fiber, which comprises a deposition step of depositing fine silica glass particles and a co-dopant (a) to prepare an aggregate of fine silica glass particles doped with the co-dopant (a); and a immersion step of immersing the aggregate of fine silica glass particles prepared in the deposition step in a solution containing the rare earth element and the co-dopant (b) to thereby dope the aggregate of fine silica glass particles with the rare earth element component and the co-dopant (b).

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: By optimizing the refractive index profile, the absorption coefficient of a rare earth element doped optical fiber can be enlarged and nonlinear effect can be suppressed. Thus, according to the present invention, the optical fiber, which is suitable for wide band optical amplification, can be realized. Moreover, in the present invention, the optical fiber of W-shape profile comprising a core, the first cladding having a refractive index smaller than that of said core surrounding said core, and the second cladding having a refractive index smaller than that of said core and larger than that of said first cladding surrounding said first cladding is prepared and are suitable for the wide band optical amplification.

Abstract: By optimizing the refractive index profile, the absorption coefficient of a rare earth element doped optical fiber can be enlarged and nonlinear effect can be suppressed. Thus, according to the present invention, the optical fiber, which is suitable for wide band optical amplification, can be realized. Moreover, in the present invention, the optical fiber of W-shape profile comprising a core, the first cladding having a refractive index smaller than that of said core surrounding said core, and the second cladding having a refractive index smaller than that of said core and larger than that of said first cladding surrounding said first cladding is prepared and are suitable for the wide band optical amplification.

Abstract: An optical fiber for optical amplification, characterized in that a full width at half maximum of gain spectrum is 45 nm or more; and a maximum value of power conversion efficiency is 80% or more. A method for producing a rare earth element-doped glass for use in manufacturing the optical fiber, which comprises a deposition step of depositing fine silica glass particles and a co-dopant (a) to prepare an aggregate of fine silica glass particles doped with the co-dopant (a); and a immersion step of immersing the aggregate of fine silica glass particles prepared in the deposition step in a solution containing the rare earth element and the co-dopant (b) to thereby dope the aggregate of fine silica glass particles with the rare earth element component and the co-dopant (b).

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 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 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: By optimizing the refractive index profile, the absorption coefficient of a rare earth element doped optical fiber can be enlarged and nonlinear effect can be suppressed. Thus, according to the present invention, the optical fiber, which is suitable for wide band optical amplification, can be realized. Moreover, in the present invention, the optical fiber of W-shape profile comprising a core, the first cladding having a refractive index smaller than that of said core surrounding said core, and the second cladding having a refractive index smaller than that of said core and larger than that of said first cladding surrounding said first cladding is prepared and are suitable for the wide band optical amplification.

Abstract: A light amplification optical fiber capable of suppressing a decrease in an amplification efficiency thereof ascribed to the concentration quenching of erbium ions, and the nonlinearity thereof is provided. At least one rare earth element, for example, Yb, which is other than the erbium ions, and which has an ion radius not smaller than 70% and not larger than 130% of that of erbium ions is doped to a core portion of an erbium ion-doped light amplification optical fiber.

Abstract: A light amplification optical fiber capable of suppressing a decrease in an amplification efficiency thereof ascribed to the concentration quenching of erbium ions, and the nonlinearity thereof is provided. At least one rare earth element, for example, Yb, which is other than the erbium ions, and which has an ion radius not smaller than 70% and not larger than 130% of that of erbium ions is doped to a core portion of an erbium ion-doped light amplification optical fiber.

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%≦1&Dgr;≧0.7%, −0.30%≦&Dgr;2≲−0.

Abstract: The present invention provides an optical fiber which has negative dispersion and negative dispersion slope in a wavelength band in use, and can carry out single-mode operation in which distortion due to the non-linear phenomenon can be suppressed so as to be suitable for wavelength multiplexed optical transmissions. When the relative index differences of center core (1), first side core (2), second side core (3), and inner cladding (4) from the silica level are &Dgr;1, &Dgr;2, &Dgr;3, and &Dgr;4, l.7%≦&Dgr;1, &Dgr;2≦−0.3%, 0.25%≦&Dgr;3, and &Dgr;4<0. Furthermore, the value A, determined by dividing the diameter a1 of the center core 1 by the diameter a2 of the first side core 2, is set to 0.15≦A≦0.2, and the value B, determined by dividing the diameter a3 of the second side core 2 by the diameter a2 of the first side core 3, is set to 1<B≦2. By such an arrangement, the absolute values of the negative dispersion and negative dispersion slope in a wavelength band of 1.

Abstract: The present invention provides an optical fiber which has negative dispersion and negative dispersion slope in a wavelength band in use, and can carry out single-mode operation in which distortion due to the non-linear phenomenon can be suppressed so as to be suitable for wavelength multiplexed optical transmissions. When the relative index differences of center core (1), first side core (2), second side core (3), and inner cladding (4) from the silica level are &Dgr;1, &Dgr;2, &Dgr;3, and &Dgr;4, l.7%≦&Dgr;1, &Dgr;2≦−O.3%, 0.25%≦&Dgr;3, and &Dgr;4<0. Furthermore, the value A, determined by dividing the diameter a1 of the center core 1 by the diameter a2 of the first side core 2, is set to 0.15≦A≦0.2, and the value B, determined by dividing the diameter a3 of the second side core 2 by the diameter a2 of the first side core 3, is set to 1<B≦2. By such an arrangement, the absolute values of the negative dispersion and negative dispersion slope in a wavelength band of 1.

Abstract: In an optical communication and the like, a light amplifying optical fiber is capable of amplifying an optical signal having a wavelength in the vicinity of at least 1.57 to 1.62 &mgr;m by a high gain. A cladding (5) is formed on the side of an outer peripheral portion of a core (1) to which erbium is added, and a refractive index of the cladding is smaller than that of the core (1). A relative refractive index difference “&Dgr;” of the core (1) with respect to the cladding (5) is made equal to 0.3% or larger, and also equal to 1% or smaller. While a composition of the core (1) is made of Er—Al2O3—GeO2—SiO2, a composition of the cladding (5) is made of SiO2, erbium is added to the entire region of the core, and concentration of this erbium is selected to be 1,000 wtppm, and also a cut-off wavelength of the optical fiber is selected to be 1,400 nm.

Abstract: The present invention provides an optical fiber for optical amplification used for an optical transmission system, for which the chromatic dispersion is controlled, and an optical amplifier in which the optical fiber for optical amplification is employed. The optical fiber according to the invention is such that the cladding has a lower refractive index than the core and is disposed so as to surround the core having a higher refractive index than that of the cladding, wherein the refractive index difference .DELTA. of the core with respect to the abovementioned cladding is from 0.4% to 1.9% and the diameter of the abovementioned core is from 4.2 to 5.0 .mu.m.