Abstract: The present invention relates to a dispersion-compensating optical fiber which can transmit, with a low loss, light signals having a high power; and an optical transmission system including the same. This dispersion-compensating optical fiber is insured its single mode at a wavelength of 1.55 &mgr;m, and comprises, about the optical axis, at least a first core having a refractive index n1, a second core having a refractive index n2 (>n1), and a cladding having a refractive index n3 (<n2). Also, this dispersion-compensating optical fiber has a chromatic dispersion of −10 ps/nm/km or less at the wavelength of 1.55 &mgr;m, whereas the ratio 2a/2b of the outside diameter 2a of the first core with respect to the-outside diameter 2b of the second core is 0.05 or more.

Abstract: An optical fiber is composed of silica glass and comprises a center core region doped with F element, a ring core region doped with GeO2, and an inner cladding region doped with F element; wherein a buffer layer composed of undoped SiO2 or SiO2 doped with one or both of P and Cl or a concentration gradient region in which GeO2 concentration radially decreases toward the boundary is provided between the center core region and the ring core region.

Abstract: The present invention relates to a Raman amplifier which is hard to deteriorate signal waveforms, so that it realizes an excellent transmission quality. In this Raman amplifier, an optical waveguide for Raman-amplifying signal light when pumping light is supplied thereto has a zero-dispersion wavelength &lgr;0 shifted from a center wavelength &lgr;center (=(&lgr;S, rms+&lgr;P, rms)/2) existing between a center-of-gravity wavelength &lgr;S, rms of the signal light, which is a mean weighted with respective powers of wavelength components included in the signal light, and a center-of-gravity wavelength &lgr;P, rms of the pumping light, which is a mean weighted with respective powers of wavelength components included in the pumping light, by such a wavelength spacing that non-degenerate type four-wave mixing is effectively suppressed.

Abstract: A method for manufacturing an optical fiber preform that can produce an optical fiber having desired characteristics over the longer length thereof. A crude preform provided with a core region and a cladding region is prepared (Step S1), and at a plurality of positions in the longitudinal direction of the crude preform, a refractive index profile in the cross-section of the crude preform is measured (Step S2). Then, the shape of the cladding region is demarcated based on the shape of the profile (Step S3). Subsequently, the crude preform is ground based on the results of the demarcation (Step S4). Thus, an optical fiber preform that enables the manufacture of an optical fiber having target characteristics is manufactured.

Abstract: The present invention relates to an optical transmission line and the like having a chromatic dispersion with a small absolute value as a whole within a signal wavelength band including S, C, and L bands.

Abstract: The invention is directed to a dispersion-compensating optical fiber which can compensate for the chromatic dispersion and dispersion slope of a non-zero dispersion-shifted optical fiber by a short length. The dispersion-shifted optical fiber constitutes an optical transmission line together with a dispersion-compensating optical fiber fusion-spliced thereto. The dispersion-compensating optical fiber has, at a wavelength of 1550 nm, a chromatic dispersion DDCF of −40 ps/nm/km or less and a ratio (DDCF/SDCF) of dispersion slope SDCF to the chromatic dispersion DDCF of 0.005/nm or more.

Abstract: A tube-shaped, GeO2-doped silica glass pipe having a high refractive index is prepared (step S2), a cylindrical silica glass rod doped with F element is inserted inside the GeO2-doped silica glass pipe (step S3), and the GeO2-doped silica glass pipe and silica glass rod in thus inserted state are heated so as to be unified (step S4). Further, thus formed assembly is inserted inside the a pure silica glass pipe (step S5), and they are heated so as to be unified (step S6), whereby an optical fiber preform is manufactured.

Abstract: A tube-shaped, GeO2-doped silica glass pipe having a high refractive index is prepared (step S2), a cylindrical silica glass rod doped with F element is inserted inside the GeO2-doped silica glass pipe (step S3), and the GeO2-doped silica glass pipe and silica glass rod in thus inserted state are heated so as to be unified (step S4). Further, thus formed assembly is inserted inside the a pure silica glass pipe (step S5), and they are heated so as to be unified (step S6), whereby an optical fiber preform is manufactured.

Abstract: The present invention concerns a negative-dispersion optical fiber for compensating in a shorter length for chromatic dispersion of a positive-dispersion optical fiber in a signal wavelength band, and an optical transmission line incorporating it. The negative-dispersion optical fiber has the following properties at the wavelength of 1550 nm; chromatic dispersion D of not more than −150 ps/nm/km; a dispersion slope satisfying such a condition that a ratio thereof (S/D) to the chromatic dispersion D is not less than 2.0×10−3/nm nor more than 4.7×1031 3/nm; and an effective area of not less than 12 &mgr;m2 but less than 25 &mgr;m2. For satisfying these properties, the negative-dispersion optical fiber has, in the order stated from the center toward the outer periphery, a core region of a maximum refractive index n1, a first cladding of a refractive index n2 (<n1), a second cladding of a refractive index n3 (>n2), and a third cladding of a refractive index n4 (<n3).

Abstract: Employed as a structure of a highly nonlinear optical fiber (nonlinear optical fiber) is a double-cladding structure in which a first cladding region 20 and a second cladding region 30 are disposed on the outer periphery of a core region 10. Since the double-cladding structure is employed, the cutoff wavelength &lgr;c can sufficiently be shortened even when, in order to increase the nonlinear coefficient &ggr;, the concentration of GeO2 added into the core is enhanced so as to raise the nonlinear refractive index, or the relative refractive index difference between the core and cladding is increased so as to reduce the effective area Aeff. This realizes an optical fiber or nonlinear optical fiber shortening its cutoff wavelength while having a sufficient nonlinearity, an optical amplifier and wavelength converter using the same, and a method of making an optical fiber.

Abstract: There is provided an optical fiber transmission-line with which the four-wave mixing generation can be suppressed effectively and also transmission loss is small. An optical fiber transmission-line 10 is dispersion-managed by a single silica optical fiber thereof being provided alternately in its longitudinal direction with parts 10a where the chromatic dispersion at the wavelength 1550 nm is positive and parts 10b where it is negative. In any one repeater span of the transmission-line there are at least four sign change positions P at which the sign of the chromatic dispersion changes in the longitudinal direction; the absolute value of the average changing rate of chromatic dispersion in each sign change locality A, each sign change locality A being a range including a sign change position P over which the absolute value of the chromatic dispersion is less than 2 ps/nm/km, is not less than 0.

Abstract: The present invention concerns a negative-dispersion optical fiber for compensating in a shorter length for chromatic dispersion of a positive-dispersion optical fiber in a signal wavelength band, and an optical transmission line incorporating it. The negative-dispersion optical fiber has the following properties at the wavelength of 1550 nm; chromatic dispersion D of not more than −150 ps/nm/km; a dispersion slope satisfying such a condition that a ratio thereof (S/D) to the chromatic dispersion D is not less than 2.0×10−3/nm nor more than 4.7×10−3/nm; and an effective area of not less than 12 &mgr;m2 but less than 25 &mgr;m2.

Abstract: An optical transmission path in a Raman gain module (1) for transmitting signal light input from an input terminal (1a) and Raman-amplifying the signal light by pumping light supplied from pumping light source units (21, 22) is formed by connecting in series two Raman amplification optical fibers (11, 12) having different wavelength dispersion values. According to this arrangement, wavelength dispersion in the amplifier module (1) can be controlled using, e.g., the combination of the wavelength dispersion values of the Raman amplification optical fibers (11, 12). Hence, accumulation of dispersion into signal light and signal light transmission in an almost zero dispersion state are prevented, and degradation in signal light transmission quality due to the nonlinear optical effect is suppressed.

Abstract: Proposed are a dispersion compensating fiber and an optical transmission system that can, using a short length of the fiber, compensate the chromatic dispersion and the dispersion slope of a non-zero dispersion shifted fiber whose chromatic dispersion is +2 ps·nm−1·km−1 to +10 ps·nm−1·km−1 and whose dispersion slope is +0.04 ps·nm−2·km−1 to +0.12 ps·nm−2·km−1 at 1550 nm. In the optical transmission system 1, an optical transmission line 30 that consists of a dispersion-shifted fiber 31 and a dispersion compensation fiber 32 is installed between stations 10 and 20. The dispersion compensating fiber 32 has the chromatic dispersion of −250 ps·nm−1·km−1˜−40 ps·nm−1·km−1 and the dispersion slope of 0.015 ps·nm−2·km−1˜0.030 ps·nm−2·km−1 at 1550 nm.

Abstract: The invention is directed to a dispersion-compensating optical fiber which can compensate for the chromatic dispersion and dispersion slope of a non-zero dispersion-shifted optical fiber by a short length. The dispersion-shifted optical fiber constitutes an optical transmission line together with a dispersion-compensating optical fiber fusion-spliced thereto. The dispersion-compensating optical fiber has, at a wavelength of 1550 nm, a chromatic dispersion DDCF of −40 ps/nm/km or less and a ratio (DDCF/SDCF) of dispersion slope SDCF to the chromatic dispersion DDCF of 0.005/nm or more.

Abstract: The present invention relates to an optical fiber having a structure suitable for long-distance optical communications, and an optical transmission line including the same. The optical fiber in accordance with the present invention comprises a core region extending along a predetermined axis, and a cladding region disposed so as to surround the outer periphery of the core region; and, as characteristics at a wavelength of 1.55 &mgr;m, an effective area of at least 110 &mgr;m2, a dispersion of 18 to 23 ps/nm/km, and a dispersion slope of 0.058 to 0.066 ps/nm2/km.

Abstract: The invention relates to agents for treating and preventing stomatitis, comprising an L-carnosine zinc salt or L-carnosine-zinc complex, or such a compound and sodium alginate. The agents are excellent in therapeutic and preventive effects on stomatitis and particularly exhibit marked effects on stomatitis caused by chemotherapy or radiotherapy for cancer.

Abstract: Neuroprotective agents based on inhibition of kainic acid neurotoxicity and compounds useful as neuroprotective agents based on inhibition of kainic acid neurotoxicity. An inhibitors of kainic acid neurotoxicity, comprising as an active ingredient a pyridothiazine derivative represented by the following general formula (I) or a pharmaceutically acceptable salt thereof, and a pyridothiazine derivative represented by the following general formula (I) or a pharmaceutically acceptable salt thereof: ##STR1## wherein symbols in the formula have the following respective meanings: the ring A: a pyridine ring; ##STR2## R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 may be the same or different and each represent a hydrogen atom or a lower alkyl, cycloalkyl, alkenyl, aryl, carboxyl or lower alkoxycarbonyl group which may have substituent(s), or are not present, with the proviso that R.sup.2 and R.sup.