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 operation mode switching apparatus comprising a structure for making it possible to minimize the waste of energy caused by troubles occurring in optical fiber lines and the like in order to efficiently utilize the energy consumed in an optical transmission system aimed for a long-term operation; a Raman amplifier including the operation mode switching apparatus; and an optical transmission system including the Raman amplifier. If an optical fiber line acting as an optical transmission medium breaks in the optical transmission system, the signal power detected from the optical fiber decreases, whereby it changes to a set value or less or the amount of decrease in signal power per unit time changes by a set value or more.

Abstract: Wavelength division multiplexing signal light is fed into an arrayed diffraction grating type optical demultiplexer, demultiplexed signal light components are outputted from a plurality of output ports, whether there is a signal light component or not is detected by each photodiode of a photodiode array, and a counter unit calculates the number of signals from the result of detection. Here, the output wavelength interval of &Dgr;&lgr;o of the output ports is set to &Dgr;&lgr;o=&Dgr;&lgr;i/m (where m is an integer of at least two) with respect to the signal wavelength interval &Dgr;&lgr;i of the wavelength division multiplexing signal light, whereas the photodiode array is sectioned into m photodiode array groups in which the output signal wavelength interval is &Dgr;&lgr;i.

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 repeatered 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: 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: Methods for connecting two optical fibers having different mode field diameters ((MFD) with low connection loss is proposed. One method comprises steps of preparing the third fiber (Fiber 3), a short length and MFD being smaller than that of the first fiber (Fiber 1) and larger than that of the second (Fiber 2), connecting the Fiber 1 to 3, connecting Fiber 2 to 3, and increasing MFD of Fiber 3 near the part connected or to be connected to Fiber 1, or MFD of Fiber 2 near the part connected or to be connected to Fiber 3 by heating the corresponding part. The other method comprises steps of preparing a short length Fiber 3 having smaller MFD than that of Fiber 1, increasing MFD of Fiber 3 near the part to be connected to Fiber 1 by heating the corresponding part, and then connecting Fiber 1 to 3, and 3 to 2 in that order.

Abstract: Provided are an optical transmission line including a connected part of the optical fibers having different refractive index profiles, wherein at least one of the optical fibers has a hollow region, and a method for connecting such optical fibers, wherein connection loss in a connection of such optical fibers is reduced. In the case of connecting an optical fiber 1, which does not have a hollow region and which consists of a core region 3 and a cladding region 4, and an optical fiber 2, which consists of a hollow core region 5 and a cladding region 6 having a plurality of refractive index variation parts 7 which extend along optical fiber 2, matching oil M is first injected into the connecting end portion of the hollow core region 5 to be connected with the optical fiber 1. The matching oil M is a substance that has a matched refractive index greater than the refractive index of the material which forms the cladding region 6.

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: In an optical fiber composed of a core region and a cladding region surrounding the core region and having a plurality of regions made of sub mediums having refractive indices different from a refractive index of a main medium disposed in a main medium constituting this cladding region, these regions made of the sub mediums are arranged in one given or a plurality of a given circular annular regions and the centers of the regions made of the sub mediums in respective circular annular regions are arranged on the same circumference centered at the center of the core.

Abstract: An optical transmission line having reduced flunctions in transmission quality is formed with a structure in which first and second waveguides whose transmission characteristics at a predetermined wavelength in a wavelength band in use are set opposite to each other and are arranged alternately. The chromatic dispersion of the first and second waveguides are set so as to have signs opposite to each other, and the dispersion slope of the first and second waveguides are set so as to have signs opposite to each other. Embodiments include setting the absolute value of chromatic dispersion in each first waveguide to 1 ps/nm/km or more but 10 ps/nm/km or less, and the absolute value of chromatic dispersion in each second waveguide is set to 1 ps/nm/km or more but 10 ps/nm/km or less.

Abstract: A dispersion compensating optical fiber comprises a minimum wavelength at which an increase amount of an actual loss value with respect to a theoretical loss value is not less than 10 mdB/km in a use wavelength band and on a long wavelength side of the use wavelength band. The actual loss value is measured in a state that the fiber is looped around a bobbin. The minimum wavelength falls within a range of 1,565 to 1,700 nm. This dispersion compensating optical fiber is suitably used for an optical transmission line of a large-capacity high-speed WDM optical transmission system.

Abstract: In an optical fiber having a core region and a cladding region which surrounds the core region, wherein a plurality of regions made of sub mediums having refractive index different from that of the main medium constituting the cladding region are spaced apart in cross section of the cladding region and the mean refractive index of the core region is lower than that of the cladding region, the sub-medium regions are regularly arranged in the radial direction of said optical fiber such that the light having given wavelength, propagation coefficient and electric field distribution propagates along the fiber axis and has not less than 50% of a total propagating power in the core region, and this arrangement does not have translational symmetry in cross section.

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: An optical fiber (1) which does not readily suffer influences of side pressures and can realize superior transmission characteristics, having a glass part (2, 3) having a core (2) and at least one cladding (3) and at least one covering layer (4a, 4b) formed around the glass part (2, 3), characterized in that the Young's modulus at 23° C. of the covering layer (4) without the glass part (2, 3) is not greater than 400 MPa. The Young's modulus measurement of the covering layer (4) is obtained by removing the glass part (2, 3) from the optical fiber (1) and putting the covering layer (4) to a tensile test.

Abstract: The present invention is related to a chromatic dispersion compensating module which realizes signal transmission at a high bit rate by its simple constitution, and an optical transmission system comprising the same. The chromatic dispersion compensating module according to the present invention comprises a chromatic dispersion compensator which compensates for the chromatic dispersion of an optical fiber transmission line at a predetermined wavelength, and a temperature controller which controls the temperature of the chromatic dispersion compensator in such a manner to set the chromatic dispersion of the chromatic dispersion compensator at a desired value. By this constitution, the dispersion compensation control in correspondence with the chromatic dispersion fluctuation in the optical fiber transmission line caused by the temperature fluctuation and the like is made possible.

Abstract: In an optical fiber having a core region and a cladding region, surrounding the core region, comprising a main medium having different refractive indices from the main medium and spaced apart in the main medium, the core region comprises a central core region having a hollow portion disposed at the center of the core region and an outer core region surrounding the central core region having a mean refractive index higher than the central core region, and the core region has a higher mean refractive index than the cladding region.

Abstract: The present invention provides an optical fiber and the like comprising a structure making it possible to realize optical communications with a higher speed and a larger capacity as compared with conventional optical transmission systems. The optical fiber according to the present invention is an optical fiber in which at least one first portion having a positive chromatic dispersion at a predetermined wavelength within a wavelength band in use and at least one second portion having a negative chromatic dispersion at the predetermined wavelength are arranged adjacent each other along the longitudinal direction thereof. In particular, the optical fiber comprises a polarization coupling structure for inducing coupling between polarization modes of propagating light. This polarization coupling structure randomly causes coupling between polarization modes of the propagating light, whereby polarization mode dispersion decreases at the predetermined wavelength.

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 dispersion compensating optical fiber has a minimum wavelength at which an increase amount of an actual loss value with respect to a theoretical loss value is not less than 10 mdB/km in a use wavelength band and on a long wavelength side of the use wavelength band. The actual loss value is measured in a state that the fiber is looped around a bobbin, and the minimum wavelength falls within a range of 1,565 to 1,700 nm.

Abstract: The present invention relates to an optical transmission line enabling WDM communications in a wide signal light wavelength band centered at a wavelength of 1.55&mgr;m, in which nonlinear optical phenomena are less likely to occur; and an optical fiber constituting a part of the optical transmission line. The optical fiber has a dispersion D (unit:ps/nm/km) and a dispersion slope S (unit:ps/nm2/km) satisfying the conditions of −69≦D≦−35 and 0.0050×D≦5≦0.0025×D; and, as characteristics with respect to light having a wavelength of 1.55 &mgr;m an effective area of 15 &mgr;m2 or more and a bending loss of 50 dB/m or less when wound at a diameter of 20 mm.

Abstract: The present invention relates to an optical fiber which enables favorable optical communications in 1.3-&mgr;m and 1.55-&mgr;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 &mgr;m to 1.60 &mgr;m, the zero-dispersion wavelength existing within a wavelength range of 1.37 &mgr;m to 1.50 &mgr;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-&mgr;m and 1.55-&mgr;m wavelength bands sandwiching the zero-dispersion wavelength.