Abstract: The present invention relates to a method of forming a transmission line capable of measuring more precise connection losses at low cost, and so on. At least of first and second optical fibers to be connected as components of the optical transmission line is selected such that, at one wavelength ? contained in the wavelength range of 1260 nm to 1625 nm, predetermined relationships defined by the Rayleigh scattering coefficients of the first and second optical fibers, the mode field diameters of the first and second optical fibers at the wavelength ?, and the transmission losses of the first and second optical fibers at the wavelength ? can be satisfied between the first and second optical fibers.

Abstract: An optical fiber suitable for use in a single fiber or multifiber optical connector or array is structured with a core region and a cladding region surrounding the core region, and exhibits a bending loss of a fundamental mode of the fiber at a wavelength ? is lower than 0.1 dB/m at a diameter of 15 mm, a mode-field diameter of the fundamental mode at an end of the fiber at the wavelength ? is between 8.0 ?m and 50 ?, and a bending loss of a first higher-order mode at the wavelength ? is higher than 1 dB/m at a diameter of 30 mm. The fiber may be multistructured, wherein the cladding region comprises a main medium and a plurality of sub medium regions therein to form a spatially uniform average refractive index.

Abstract: A optical filter has a loss spectrum whose gradient dL/d? of a loss L (dB) with respect to the wavelength ? (nm) is variable in the wavelength band of multiplexed signal light. A control circuit detects each power of signal light components demultiplexed by an optical coupler and controls the power of optical pumping light to be supplied to an optical amplification section from an optical pumping light sources such that the power of output signal light has a predetermined target value. The control circuit also controls the gradient dL/d? of the optical filter on the basis of powers of the signal light components.

Abstract: An optical fiber suitable for use in a single fiber or multifiber optical connector or array is structured with a core region and a cladding region surrounding the core region, and exhibits a bending loss of a fundamental mode of the fiber at a wavelength ? is lower than 0.1 dB/m at a diameter of 15 mm, a mode-field diameter of the fundamental mode at an end of the fiber at the wavelength ? is between 8.0 ?m and 50 ?, and a bending loss of a first higher-order mode at the wavelength ? is higher than 1 dB/m at a diameter of 30 mm. The fiber may be multistructured, wherein the cladding region comprises a main medium and a plurality of sub medium regions therein to form a spatially uniform average refractive index.

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: The present invention relates to an optical fiber which enables favorable optical communications in 1.3-?m and 1.55-?m wavelength bands, and an optical transmission system including the same. The optical fiber according to the present invention has only one zero-dispersion wavelength within a wavelength range of 1.20 ?m to 1.60 ?m, the zero-dispersion wavelength existing within a wavelength range of 1.37 ?m to 1.50 ?m , and has a positive dispersion slope at the zero-dispersion wavelength, thereby enabling favorable optical communications utilizing each signal light in the 1.3-?m and 1.55-?m wavelength bands sandwiching the zero-dispersion wavelength.

Abstract: In an optical fiber including a core region and cladding regions of not less than three layers which surrounds the core region in order, each of said cladding regions has a mean refractive index different from those of the adjacents regions,at least one of the cladding regions has a lower mean refractive index than both adjacent regions, and at least one cladding region is provided with a plurality of sub medium regions each having a refractive index lower than a main medium constituting this cladding region.

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 ?m and adjusts loss fluctuations among wavelengths in the wavelength band of 1.55 ?m into an appropriate range. The 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 ?m. An example of the 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. Consequently, the loss fluctuations among individual wavelengths in the whole transmission line including the dispersion-compensating module are adjusted by the loss-equalizing device in the dispersion-compensating module so as to fall within an appropriate range.

Abstract: The present invention discloses an optical transmission line constructing method comprising the steps of connecting a plurality of optical fibers differing from each other in terms of a transmission characteristic; making inspection light incident on an entrance end of the connected plurality of optical fibers; detecting, on the entrance end side, respective return light components of the inspection light occurring at individual positions of the plurality of optical fibers in its longitudinal direction; evaluating a characteristic information distribution of return light in the longitudinal direction of the plurality of optical fibers; and constructing an optical transmission line according to a result of the evaluation.

Abstract: The present invention relates to an optical fiber and the like comprising a structure enabling high-density packaging into an optical cable while making it possible to transmit signals with a high bit rate in both of wavelength bands of 1.3 &mgr;m and 1.55 &mgr;m. For example, this optical fiber is configured so as to have a mode field diameter of 8.0 &mgr;m or less at a wavelength of 1.55 &mgr;m, a cutoff wavelength of 1.26 &mgr;m or less, and a chromatic dispersion with an absolute value of 12 ps/nm/km or less at wavelengths of 1.3 &mgr;m and 1.55 &mgr;m, thereby yielding an excellent lateral pressure resistance enabling high-density packaging into an optical cable.

Abstract: An optical transmission line including a portion formed by fusion-splicing optical fibers having structures different from each other; wherein, in the optical fibers having structures different from each other, a first optical fiber 1 has a mode field diameter smaller than that of a second optical fiber 2 fusion-spliced thereto; and wherein the first optical fiber 1 has an average viscosity from a center to an outermost layer greater than that of the second optical fiber from a center to an outermost layer.

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: An optical fiber has a section of the first kind having a chromatic dispersion not less than a given positive value x and a negative chromatic dispersion slope at a given wavelength and a section of the second kind has a chromatic dispersion not more than −x and a positive chromatic dispersion slope at the same wavelength. Another optical fiber has a chromatic dispersion higher than a positive value x and a negative chromatic dispersion slope at a given wavelength band.

Abstract: A Raman amplifier having a great Raman amplification gain is disclosed. An optical transmission system 1 is provided with an optical fiber 31 for Raman amplification and an optical multiplexer 41 between a transmitter 10 and a receiver 20 in the order of enumeration, and further provided with a pump light source 51 for Raman amplification that is connected with the optical multiplexer 41. The wavelength of signal light to be transmitted from the transmitter 10 to the receiver 20 is at 1.65 &mgr;m band, and the wavelength of the pump light that is output from the light source 51 is C-band or L-band. Since the pump light for Raman amplification propagates at a low loss through the optical fiber for Raman amplification, a great Raman amplification gain can be attained by the Raman amplifier.

Abstract: The present invention relates to an optical fiber or the like which allows more precise compensation for the chromatic dispersion of a transmission optical fiber over a broad wavelength band. The optical fiber has a chromatic dispersion of −100 ps/nm/km or less in a wavelength band of 1535 to 1565 nm, 1565 to 1610 nm, 1554 to 1608 nm or 1535 to 1610 nm. In particular, the chromatic dispersion profile of the fundamental mode of this optical fiber defined by the orthogonal coordinate system of the wavelength and chromatic dispersion value has a shape such that, over the entire wavelength band except for the shortest and longest wavelengths thereof, the chromatic dispersion values on the chromatic dispersion profile are respectively located on the minus side of the associated chromatic dispersion values on a straight line connecting the chromatic dispersion values at the shortest and longest wavelength.

Abstract: An optical fiber has a section of the first kind having a chromatic dispersion not less than a given positive value x and a negative chromatic dispersion slope at a given wavelength and a section of the second kind has a chromatic dispersion not more than −x and a positive chromatic dispersion slope at the same wavelength. Another optical fiber has a chromatic dispersion higher than a positive value x and a negative chromatic dispersion slope at a given wavelength band.

Abstract: An optical fiber suitable for use in a single fiber or multifiber optical connector or array is structured with a core region and a cladding region surrounding the core region, and exhibits a bending loss of a fundamental mode of the fiber at a wavelength &lgr; is lower than 0.1 dB/m at a diameter of 15 mm, a mode-field diameter of the fundamental mode at an end of the fiber at the wavelength &lgr; is between 8.0 &mgr;m and 50 &lgr;, and a bending loss of a first higher-order mode at the wavelength &lgr; is higher than 1 dB/m at a diameter of 30 mm. The fiber may be multistructured, wherein the cladding region comprises a main medium and a plurality of sub medium regions therein to form a spatially uniform average refractive index.

Abstract: The present invention relates to a wide-band, low-loss, submarine optical cable excellent in productivity, an optical fiber unit employed in the submarine optical cable, and a method of making the optical fiber unit. The optical fiber unit employed in the submarine optical cable comprises a loose structure in which one or more coated optical fibers are accommodated together with a soft resin in a space formed within a plastic support. In particular, one or more compression members are embedded in the plastic support along the space accommodating the coated optical fibers. The compression members closely in contact with the plastic support prevents the shrinkage of the plastic support from occurring due to temperature changes before forming a cable utilizing the optical fiber unit.

Abstract: Disclosed are an optical transmission system and a Raman amplifying control unit that can stabilize the effective loss of a transmission line even if the optical transmission system has a relay station between a transmitting station and a receiving station. The optical transmission system and the Raman amplifying control unit have an introducing means for outputting inspection light and introducing it to the transmission line, a receiving means for receiving the back-scatter from the inspection light, and a control means for inspecting the transmission line and controlling an exciting light supplying means according to the received backscattering light. The introducing means, the receiving means, and the control means are provided together with the exciting light supplying means in a station at the transmitting side or receiving side of a relay section in the optical transmission system.

Abstract: In an optical fiber including a core region and a cladding region surrounding said core region in a cross section and having a cross-sectional structure in which a plurality of regions constituted by sub mediums are arranged in main mediums, at least one of refractive indices of the main mediums and the sub mediums are changed in a radial direction.