Abstract: A 1.55 ?m band dispersion shifted optical fiber is provided which has a low loss and low dispersion slope. A core region “a” is heavily doped with GeO2 . A core region “b” is composed of pure SiO2 glass. A cladding section is arranged around the core region. The cladding section has a lot of holes extending in the longitudinal direction of the optical fiber. The holes of the cladding section are not located at random, but have a honeycomb structure composed of regular hexagons which have a side length of ?, and serve as a primitive lattice. The center of the core section has a region having a refractive index higher than that of the periphery of the core section. The core section has the refractive index distribution in which the group velocity dispersion at the operation wavelength of the region becomes the normal dispersion.

Abstract: A 1.55 ?m band dispersion shifted optical fiber is provided which has a low loss and low dispersion slope. A core region “a” is heavily doped with GeO2 . A core region “b” is composed of pure SiO2 glass. A cladding section is arranged around the core region. The cladding section has a lot of holes extending in the longitudinal direction of the optical fiber. The holes of the cladding section are not located at random, but have a honeycomb structure composed of regular hexagons which have a side length of ?, and serve as a primitive lattice. The center of the core section has a region having a refractive index higher than that of the periphery of the core section. The core section has the refractive index distribution in which the group velocity dispersion at the operation wavelength of the region becomes the normal dispersion.

Abstract: An optical fiber/glass tube fusion spliced structure includes an optical fiber made of glass and a glass tube through which the optical fiber is inserted and at least in part of the optical fiber/glass tube fusion spliced structure, an outer circumference portion of the optical fiber and an inner circumference portion of the glass tube are fusion spliced. Part of the fusion spliced portion located in one of the optical fiber and the glass tube is formed of a material having a lower fusion point than a fusion point of part of the fusion spliced portion located in the other.

Abstract: An optical fiber/glass tube fusion spliced structure includes an optical fiber made of glass and a glass tube through which the optical fiber is inserted and at least in part of the optical fiber/glass tube fusion spliced structure, an outer circumference portion of the optical fiber and an inner circumference portion of the glass tube are fusion spliced. Part of the fusion spliced portion located in one of the optical fiber and the glass tube is formed of a material having a lower fusion point than a fusion point of part of the fusion spliced portion located in the other.

Abstract: A polarization-maintaining optical fiber and absolutely single-polarization optical fiber are provided which enable long distance transmission maintaining a polarization state of signal light. The polarization-maintaining optical fiber includes a core, photonic crystal cladding, and jacket. The photonic crystal cladding is divided into four segments by broken lines from the center to the periphery. Among a plurality of grating holes in a pair of segments opposed to each other with respect to the core, the diameter of grating holes close to the core is greater than the diameter of grating holes in another pair of segments opposed with each other, and than a grating constant.

Abstract: A polarization-maintaining photonic crystal fiber 10 includes six thin holes 4a and 4b adjacent to a core 1. Among these holes 4a and 4b, a pair of holes 4b at opposite sides of the core 1 have a diameter greater than that of the other four thin holes 4a, and therefore, the polarization-maintaining photonic crystal fiber 10 has polarization-maintaining ability. An overclad layer 3 exists around the clad layer 2 which includes a large number of thin holes 4a and 4b around the core 1. The overclad layer 3 includes a pair of marking portions 5 at opposite sides of the core 1. The marking portions 5 are holes which can be seen at positions different from the clad layer 2 when the fiber 10 is viewed from a position right above the fiber 10 in the drawing. In this way, the direction of the polarization plane of the polarization-maintaining photonic crystal fiber 10 is identified.

Abstract: A polarization-maintaining optical fiber and absolutely single-polarization optical fiber are provided which enable long distance transmission maintaining a polarization state of signal light. The polarization-maintaining optical fiber includes a core, photonic crystal cladding, and jacket. The photonic crystal cladding is divided into four segments by broken lines from the center to the periphery. Among a plurality of grating holes in a pair of segments opposed to each other with respect to the core, the diameter of grating holes close to the core is greater than the diameter of grating holes in another pair of segments opposed with each other, and than a grating constant.

Abstract: The present invention provides a method for manufacturing a photonic crystal fiber that has a core portion in which a fiber core extends in a lengthwise direction and is formed as a solid or a void, and a porous clad portion provided around the core portion and having numerous pores extending along the core portion. A preform is fabricated by packing numerous capillaries into a cylindrical support pipe such that they are parallel to the central axis of the support pipe and disposing a core rod to serve as the solid core portion at the central axis portion of the support pipe. The preform is drawn to make it small in diameter.