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: 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: The present invention provides a Raman amplification pumping module and others with a structure for effectively suppressing degradation of quality of signal light even with a breakdown in either one of a plurality of light sources. The Raman amplification pumping module is provided with light sources for emitting respective lightwaves with center wavelengths different from each other, and each of the center wavelengths of the lightwaves from these light sources is adjusted so that a difference between two center wavelengths selected therefrom is less than 6 nm.

Abstract: An optical switch according to this invention has a planar waveguide in which an optical path is formed. A trench is formed in the upper surface of this planar waveguide. A cantilevered movable member is mounted on the planar waveguide. A comb is formed in the end portion of this movable member. A mirror which intercepts light propagating on the optical path is fixed to the end of the movable member. An electrode opposing the movable member is formed on the planar waveguide. A comb is formed in that portion of this electrode, which opposes the comb of the movable member. The movable member and electrode are connected via a voltage source. When this voltage source generates electrostatic force between the movable member and electrode, the movable member bends, and the mirror moves along the bottom surface of the trench accordingly.

Abstract: The present invention relates to an optical multiplexer/demultiplexer comprising a structure for effectively lowering the crosstalk between adjacent signal channels, thereby realizing excellent wavelength multi/demultiplexing characteristics. The optical multiplexer/demultiplexer is designed such that, while adjacent channel waveguides are allowed to have optical path length differences different from each other, effective optical path length differences become constant between optical paths traveling by way of the channel waveguides adjacent each other in optical paths including slab waveguides as a whole, whereby the structure for connecting channel waveguides to flat connecting end faces of slab waveguides can be changed arbitrarily without being restricted by multi/demultiplexing conditions.

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 relates to an optical fiber line for transmitting a plurality of wavelengths of optical signals in a wavelength division multiplexing transmission system, an optical transmission line, a method of making an optical cable, and a method of laying an optical transmission line.

Abstract: Three Mach-Zehnder interferometers 141 to 143 are connected in a series between an optical input terminal and an optical output terminal in an optical filter. Each interferometer is composed of two optical paths optical coupled at both ends by optical couplers. Only one interferometer has same optical path lengths between optical couplers. Heaters are disposed on each optical paths to allow the slope of transmission loss to change through the adjustment of the phase shift between those respective optical paths.

Abstract: The present invention relates to a Raman amplification method realizing Raman amplification of WDM signal light in a wider amplification wavelength band with a simpler configuration, and the like. A Raman amplifier realizing the Raman amplification method comprises a Raman amplification optical fiber, and a pumping light source for supplying pumping light having a wavelength &lgr;p to the amplification optical fiber. In the Raman amplifier, a part of the signal light is Raman-amplified with the pumping light having the wavelength &lgr;p, whereas a part of the Raman-amplified light is utilized as pumping light. This Raman-amplifies signal light including a channel wavelength with a wavelength of (&lgr;p+&Dgr;&lgr;+20 nm) or longer, where &Dgr;&lgr; is the Raman shift amount of wavelength caused by the pumping light at the wavelength &lgr;p.

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: An optical communication system has a configuration in which an optical transmission line is laid between a repeater (transmitter) and another repeater (receiver). The optical transmission line is formed by fusion-splicing a first optical fiber on the upstream side and a second optical fiber on the downstream side. The first optical fiber has a transmission loss of 0.25 dB or less, and an effective area of 80 &mgr;m2 or above (preferably 100 &mgr;m2 or above), at a wavelength of 1550 nm, which is the wavelength of signal light. The second optical fiber is connected to the downstream end of the first optical fiber and has positive dispersion regions and negative dispersion regions which are alternately arranged along the longitudinal direction and whose chromatic dispersions at a wavelength of 1550 nm are positive and negative, respectively.

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: The present invention relates to a WDM transmission system and the like suitable for optical communications between local stations having a relatively short repeater interval. In particular, the WDM transmission repeater employed in the WDM transmission system demultiplexes a plurality of signal lights propagating through a transmission line into first and second groups, takes out the second group, comprises a multiplexer for sending into the transmission line a new WDM signal group in which the first group thus demultiplexed and a third group of signal lights different from those of the first group are multiplexed, and has a special structure for reducing the influence of the not-demultiplexed crosstalk components within the second group upon the optical communications.

Abstract: A planar lightwave circuit (PLC) of a PLC module is provided with many waveguides including a plurality of input (output) optical waveguide on a substrate. Junction faces between these input (output) optical waveguide and input (output) optical fibers are slant against the optical axis thereof. The PLC module has photodetectors opposed to corresponding junction faces disposed at the input-optical-fiber's-side (output-optical-waveguide's-side).

Abstract: An optical signal, which is to become the subject of dispersion compensation, is split by optical combining/splitting unit 2, and each frequency component of the optical signal that is split is reflected by each reflective surface of reflective mirror 40 of reflective means 4 to apply a predetermined phase shift to the respective frequency components. Each reflected frequency component is then combined using optical combining/splitting unit 2, to give dispersion compensated optical signal. Furthermore, in regards to reflective means 4, which is used to apply phase shift to each frequency component of an optical signal, reflective mirror 40 is made a variable movable mirror by reflection position at each reflective surface, which is reflects the frequency components, deforming the entire reflective surface. This allows dispersion that is created in an optical signal to be compensated with favorable controllability and high accuracy.

Abstract: The invention provides an apparatus for and method of monitoring wavelength multiplexed signal light, which can obtain monitored data for multi-channel optical signals contained in the wavelength multiplexed signal light, which can avoid a large size and complicated structure and high cost of monitoring apparatus, and which can easily monitor the wavelength multiplexed signal light. The invention also provides an optical transmission system employing the monitoring apparatus and method. An optical filter being able to control a loss pattern is disposed on a monitoring waveguide for the wavelength multiplexed signal light, which is branched for monitoring from an input waveguide and an output waveguide constituting a main optical transmission path in a wavelength multiplexed signal light monitoring apparatus.

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: An optical switch that can restrain the occurrence of cross talk is provided. A first waveguide path 11 and a second waveguide path 12 are provided on a waveguide substrate PCL so as to intersect each other at a given angle. A trench T is formed in a straight line in the surface of the waveguide substrate PCL so as to cross the central axes of the first waveguide path and the second waveguide path. The trench T is as deep as to expose the whole end face of the first waveguide path and the second waveguide path. The first waveguide path 11 and the second waveguide path 12 are arranged such that their central axes are arranged asymmetrically with respect to the straight line.

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: The present invention relates to a dispersion compensating fiber for improving a transmission system with it in total chromatic dispersion and dispersion slope in the 1.55 &mgr;m wavelength band. The dispersion compensating fiber according to the present invention is characterized by having the following characteristics for light in the 1.55 &mgr;m wavelength band: chromatic dispersion not less than −40 ps/km/nm and not more than 0 ps/km/nm; dispersion slope not less than −0.5 ps/km/nm2 and not more than −0.1 ps/km/nm2; transmission loss not more than 0.5 dB/km; polarization mode dispersion not more than 0.7 ps.km−½; mode field diameter not less than 4.5 &mgr;m and not more than 6.5 &mgr;m; cut-off wavelength not less than 0.7 &mgr;m and not more than 1.7 &mgr;m in the length of 2 m; and bending loss at the diameter of 20 mm, not more than 100 dB/m.