Mikio Ogai

Development and performance of fully fluorine-doped single-mode fibers

Fluorine doping has been used to obtain vapor-phase-axial-deposited (VAD) single-mode fibers with a loss less than 0.20 dB/km at 1.55 mu m. A nonshifted design in which fluorine dopant was added mainly to the cladding and only slightly to the pure silica core part was fabricated with high yield. A similar approach has been successfully applied to dispersion-shifted fibers with a dual-shape-core index profile with encouraging results for reducing the transmission loss down to 0.20 dB/km. >

Behavior of alkali impurities and their adverse effect on germania-doped silica fibers

Alkalies, such as sodium and potassium, were found to migrate from over-jacketing natural silica tubes into germania-doped cores forming defects leading to hydrogen-induced loss in the infrared wavelength region. These impurities were found to be removed from the same kind of natural silica tubes during the MCVD process. Results strongly point out that the absence of impurities is essential for 1.55-μm transmission systems based on germania-doped silica fiber.

Structural defects in optical fiber glasses

Phosphorus doping to SiO 2 -GeO 2 core glass in optical fiber raised hydrogen and radiation induced-loss increases. The precursor of germanium electron center ( Ġe ) and phosphorus associated center ( . P ) produced with the phosphorus doping was found to be origin of the raised induced-losses. Silicon associated defect (Sidbnd;) generated from peroxy linkage during drawing process in optical fiber seemed to react with hydrogen to produce silylidyne group with absorption peak at 1.52 μ m.

Hydrogen Problems and Longterm Reliability of Fiber Cables

Fiber losses increase if hydrogen diffuses inside fibers. The following four methods are effective in preventing these loss increases. (1) Do not use P205 as a dopant, or use a minimum amount if it is used. (2) Use fluorine as a dopant. (3) Use a synthetic cladding layer. (4) Carefully select the material to cover fibers. Plastic materials that do not generate H2 should be selected for cables. Generally, UV curable resines generate less H2 as materials to cover fibers. Using these conditions, loss increases of GI fibers and SM fibers with H2 1 atm., 20 °C at 1.3 and 1.55 μm in 25 years will be <0.01 dB/km.

LOW LOSS DISPERSION SHIFTED FIBER WITH FLUORINE DOPED CLADDING AND STEP LIKE INDEX PROFILE

Various types of dispersion shifted fibers for 1.55 μm operation have been proposed with variety of refractive index profiles such as triangle, trapezoidal, segmented core1), quadruple clad. Dispersion characteristics of these fibers were well analized and good reproducibility has been reported.

Low-loss fully fluorine-doped dispersion-shifted fibers

Fluorine doping in both the dual-shape core and cladding parts of dispersion-shifted single-mode fibers was found to lower the transmission losses at 1.55 µm and suppress the hydrogen-induced losses due to the reaction in the IR wavelength region.

Effects of hydrogen on long-term reliability of opticalfiber cable

It has recently been discovered that hydrogen affects the transmission performance of silica fiber, and many studies have been done to clarify the source of hydrogen in cable, diffusion of hydrogen into silica fiber, and the reaction mechanism forming various hydroxyl species. Long-term reliability of optical fiber cable affected by hydrogen is reviewed in this paper.