Abstract: After a wide-band DCF is wound around a bobbin to form an optical fiber coil 32, the latter is removed from the bobbin and placed into a bundle state (the state where the increase in transmission loss in the wavelength band of 1.55 &mgr;m caused by distortions in winding is reduced by 0.1 dB/km or more) released from distortions in winding. A resin 42 is used as a coil-tidying member so as to secure the optical fiber coil 32 to a storage case 40 at four positions. Both ends of the optical fiber coil 32 are connected to pigtail fibers at fusion-splicing parts 44; respectively. Even when the storage case 40 is closed with a lid after the optical fiber coil 32 is secured to the storage case 40 with the resin 42, there remain interstices within the bundle of the optical fiber coil 32 and a space between the optical fiber coil 32 and the storage case 40. As a result, even when the optical fiber coil 32 in a bundle state is accommodated in the storage case 40, transmission loss and the like would not increase.

Abstract: The present invention relates to a dispersion-managed optical fiber which can be manufactured easily and has a structure which enables the easy connection thereof with other optical fiber and the like. The dispersion-managed optical fiber is a silica-based optical fiber ensuring its single mode at a predetermined wavelength within a signal wavelength band, in which first portions each having a positive chromatic dispersion and second portions each having a negative chromatic dispersion are arranged alternately and adjacent to each other. In the dispersion-managed optical fiber, the dopant concentration is made uniform in the longitudinal direction and, corresponding to the above-mentioned first and second portions, the refractive index of a glass layer not doped with GeO2 as a dopant is adjusted or the residual stresses in glass layers are changed.

Abstract: The present invention relates to an optical fiber comprising a structure which effectively suppresses the occurrence of nonlinear phenomena without increasing transmission loss such as macrobending loss. The optical fiber according to the present invention comprises, radially in succession from the center axis thereof, a center region having a predetermined refractive index, a first annular region having a higher refractive index than the center region, and a second annular region doped with fluorine and having a lower refractive index than the first annular region. In particular, this optical fiber has an effective area of 70 &mgr;m2 or more with respect to light having a wavelength of 1550 nm, whereas the fluorine contents in the second annular region is adjusted such that the refractive index thereof decreases with distance from the center of the optical fiber.

Abstract: The present invention relates to a dispersion-compensating module having a structure which compensates for the dispersion of an optical transmission line in a wavelength band of 1.55 &mgr;m and adjusts loss fluctuations among wavelengths in the wavelength band of 1.55 &mgr;m into an appropriate range. The dispersion-compensating module comprises a structure adapted to be installed in an already installed optical fiber transmission line, and has a loss slope with a polarity opposite to that of the optical fiber transmission line in the wavelength band of 1.55 &mgr;m. A configurational example of the dispersion-compensating module comprises a dispersion-compensating optical fiber as a dispersion-compensating device, and an optical fiber doped with a transition metal element as a loss-equalizing device.

Abstract: In an optical fiber comprising a core region, an inner cladding region, and an outer cladding region which extend along its fiber axis, the average refractive index n0 of core region, the average refractive index n1 of inner cladding region, and the average refractive index n2 of outer cladding region satisfying the relationship of n1<n2<n0; at least three microstructures each extending along the fiber axis and comprising an auxiliary medium having a refractive index different from that of a main medium constituting the inner cladding region are included in the inner cladding region.

Abstract: A twist imparting roller 220 with two rotational axes C1, C2 is used as a roller for guiding a coated optical fiber 200. The twist imparting roller 220 rotates about the first rotational axis C1 to guide the coated optical fiber 200 and rotates along a circular locus indicated by a dashed line L2, about the second rotational axis C2 to impart twists to the optical fiber. The coated optical fiber 200 is wound through a turn along a V-groove 221 around the twist imparting roller 220. This suppresses rolling of the coated optical fiber 200 relative to the roller surface of the twist imparting roller 220, so as to efficiently impart the twists to the optical fiber and adequately reduce polarization mode dispersion in the optical fiber.

Abstract: This invention relates to an optical transmission line having a structure that reduces dispersion with respect to signal light in a 1.55-&mgr;m band. Each transmission unit includes a dispersion-shifted optical fiber as a transmission medium and a mode removing unit for reducing the optical power of high-order modes excluding a fundamental mode of light signals propagating through the dispersion-shifted optical fiber. The dispersion-shifted optical fiber has an incident terminal on which the light signals are incident and an exit terminal from which the light signals are emitted, and has a cutoff wavelength longer than the wavelength of the light signals at a fiber length of 2 m. The mode removing unit has a structure for reducing the optical power of high-order modes to 1/10 or less, preferably 1/40 or less, of the optical power of the fundamental mode so as to satisfy the single-mode condition in relation to fiber length.

Abstract: The present invention relates to an optical transmission line comprising a structure for effectively lowering both of nonlinearity and dispersion slope, and an optical transmission system including the same. The optical transmission line comprises, as a repeating transmission line disposed between stations, a single-mode optical fiber having a zero-dispersion wavelength in a 1.3-&mgr;m wavelength band and a dispersion-compensating optical fiber for compensating for the chromatic dispersion of the single-mode optical fiber. The optical transmission line has an average dispersion slope Save of −0.0113 ps/nm2/km or more but 0.0256 ps/nm2/km or less at a wavelength of 1550 nm, and an equivalent effective area EAeff of 50 &mgr;m2 or more at the wavelength of 1550 nm, whereas the average dispersion slope Save and the equivalent effective area EAeff are designed so as to satisfy a predetermined condition such that the bending loss falls within a permissible range of 2 dB/m or more but 10 dB/m or less.

Abstract: The present invention provides a chromatic-dispersion measuring apparatus and method that can quickly measure chromatic dispersion in an optical fiber even when the optical fiber is short. Continuous light beams having the wavelengths &lgr;1 and &lgr;2 output from light sources are multiplexed by a multiplexer, are intensity-modulated by an intensity modulator, and are then output as optical signals. The output optical signals with the wavelengths &lgr;1 and &lgr;2 enter an optical fiber to be measured, and propagate therethrough. The optical signals emerging from the optical fiber are de-multiplexed by a de-multiplexer, and are received by corresponding photodetectors. Subsequently, the phase difference between the optical signals received by the photodetectors is detected by a phase detector. The chromatic dispersion of the optical fiber is calculated by an arithmetical circuitry on the basis of the detection result.

Abstract: The present invention relates to a dispersion-shifted optical fiber suitable for an optical transmission line having an optical fiber amplifier with a wider amplification band. In particular, the dispersion-shifted optical fiber according to the present invention has a zero-dispersion wavelength of 1610 nm or more but 1750 nm or less, and a cutoff wavelength of 1.1 &mgr;m or more at a length of 2 m in order to suppress the bending loss to a practically permissible range, and has, with respect to light having a wavelength of 1550 nm, an effective area of 45 &mgr;m2 or more and a dispersion slope of 0.15 ps/nm2/km or less in order to suppress the occurrence of nonlinear phenomena.

Abstract: A dispersion-managed optical fiber transmission-line with which the formation of side bands around the optical signal wavelength can be suppressed even when carrying out high-speed signal transmission.

Abstract: The present invention provides an optical fiber which has a hollow portion extending along the axis and which reduces degradation of the optical characteristics, and a production method thereof. An optical fiber includes a hollow core portion, and a cladding portion which surrounds the hollow core portion. The refractive index of the hollow core portion is lower than that of the cladding portion. The hollow core portion is closed at both ends of the optical fiber so as to form sealed portions. The sealed portions are formed by, for example, heating the optical fiber and softening the cladding portion. This prevents foreign material and the like from entering the hollow core portion. Ferrules of optical connectors are attached to both end faces of the optical fiber.

Abstract: A dispersion-managed optical fiber transmission-line with which the formation of side bands around the optical signal wavelength can be suppressed even when carrying out high-speed signal transmission.

Abstract: A multiple fiber optical cable includes bundled plural optical fibers. In each of the optical fibers to be bundled in the optical cable, a positive dispersion section having a positive chromatic dispersion in an optical signal wavelength and a negative dispersion section having a negative chromatic wavelength and a negative dispersion section having a negative chromatic dispersion section in the optical signal wavelength are alternately arranged so that the chromatic dispersion characteristic of the optical fiber alternately changes in the longitudinal direction. The chromatic dispersion characteristics of the respective bundled plural optical fibers coincide with each other at at least the position of each end of the multiple fiber optical cable. The member which surrounds the optical fibers of the optical cable is provided with the identification marks for identifying the chromatic dispersion characteristics at the individual locations in the longitudinal direction.

Abstract: A dispersion-managed optical fiber transmission-line with which the formation of side bands around the optical signal wavelength can be suppressed even when carrying out high-speed signal transmission. An optical fiber transmission-line 1 constitutes one repeater span installed between a transmitter (or repeater) 2 and a receiver (or repeater) 3 and is made up of N sections 41 through 4N in sequence from the transmitter 2 to the receiver 3. The chromatic dispersion at the wavelength 1.55 &mgr;m is positive in the sections 4n where the value of n is odd and is negative in the sections 4n where the value of n is even. The ratio between the maximum value and the minimum value of the average chromatic dispersions Dn of the sections 4n is at least 1.3 and not greater than 10.0.

Abstract: The present invention relates to an optical fiber having, at least, a structure for effectively restraining microbend loss from increasing. This optical fiber is an optical fiber suitable for a dispersion-flattened fiber, a dispersion-compensating fiber, and the like, and insured its single mode in a wavelength band in use. In particular, since the fiber diameter is 140 &mgr;m or more, this optical fiber has a high rigidity, so that the increase in microbend loss is effectively suppressed, whereas the probability of the optical fiber breaking due to bending stresses is practically unproblematic since the fiber diameter is 200 &mgr;m or less. Also, since this optical fiber has a larger mode field diameter, it lowers the optical energy density per unit cross-sectional area, thereby effectively restraining nonlinear optical phenomena from occurring.

Abstract: The present invention relates to an optical transmission line suitably used for a large-capacity high-speed WDM optical transmission system, and an optical fiber suitably used for such an optical transmission line. The optical transmission line is formed by connecting a single-mode optical fiber (SMF) and a dispersion compensating optical fiber (DCF). The dispersion compensating optical fiber has a dispersion value DDCF (unit: ps/nm/km) and dispersion slope SDCF (unit: ps/nm2/km) falling within the ranges of −82 ≦DDCF≦−29 and 0.0023×DDCF≦SDCF≦0.033+0.0015×DDCF at a wavelength of 1,550 nm, respectively. At the wavelength of 1,550 nm, the transmission loss is 0.5 dB/km or less. Letting LDCF be the length of the dispersion compensating optical fiber, and LSMF be the length of the single-mode optical fiber, the value LDCF/(LDCF+LSMF) in the optical transmission line is 0.2 to 0.4.

Abstract: The present invention relates to a Raman amplification optical fiber and the like comprising a structure which can Raman-amplify signal light including a plurality of wavelength components at a high efficiency and effectively restrain signal waveforms from deteriorating due to influences of nonlinear optical phenomena, while improving the degree of freedom in the design of optical fiber transmission lines and Raman amplifiers. As characteristics at each wavelength of signal light, the Raman amplification optical fiber has a chromatic dispersion with an absolute value of 6 ps/nm/km or more but 20 ps/nm/km or less, and an effective area Aeff of 20 &mgr;m2 or less, preferably less than 15 &mgr;m2. More preferably, as a characteristic at each wavelength of signal light, the Raman amplification optical fiber has a Raman gain coefficient GR/Aeff of 0.005 (W·m)−1 or more.

Abstract: The present invention relates to a dispersion-compensating module having a structure which compensates for the dispersion of an optical transmission line in a 1.55-&mgr;m wavelength band and adjusts loss fluctuations among signal wavelengths in the 1.55-&mgr;m wavelength band into an appropriate range. The dispersion-compensating module comprises a structure adapted to be installed in an already installed optical fiber transmission line, and has a loss slope with a polarity opposite to that of the optical fiber transmission line in the 1.55-&mgr;m wavelength band. One application of the dispersion-compensating module comprises a dispersion-compensating optical fiber as a dispersion-compensating device, and an optical fiber doped with a transition metal element as a loss-equalizing device.

Abstract: This invention relates to an optical fiber having a structure that effectively reduces transmission loss and bending loss. An optical fiber according to this invention is an optical fiber mainly comprised of silica and including a core region and a cladding region covering the core region. The core region is doped with chlorine so as to have a refractive index higher than that of pure silica. The cladding region is doped with fluorine so as to have a refractive index lower than that of pure silica. The optical fiber, in particular, is characterized in that a peak value of a relative refractive index difference of the core region with respect to a refractive index of pure silica is 0.05% or more.