Phenomenon of silica-fiber loss increase, which is induced by an electric current applied in water, is reported. It is found from experimental results that the loss increase is caused by hydrogen molecules, which are electrolytically produced and are diffused into the fiber interstitially. Furthermore, both infrared loss and Ramanscattering spectra are measured for a fiber dissolved by H2, HD, and D2 molecules to make clear assignment for loss peak. As a result, it is found that the absorption loss peaks are associated with a connection between molecular vibration and SiO4 tetrahedral vibrations in the silica glass.

We examine effects of higher order dispersion and optical non-linearity, including linear attenuation on intense short pulses propagating along solid and Noble-gas-filled wave-guides. In order to simulate realistic pulse and spectral shapes, we have taken into account quadratic and cubic dispersion as well as Raman (solid wave-guide) and shock nonlinear terms in the generalized Schrodinger equation of propagation. The phonon oscillation corresponding to 13. 3 THz in SiO2 gets superimposed on to the exit pulse in the normal dispersion regime of solid fiber for lengths exceeding 6LDLNL. The super continuum spectrum from hollow Noble-gas-filled fibers shows remarkably deep modulations.

The characteristics of W-type single-mode fiber with low-dispersion below 2 ps/km/nm over the 1.5-1.6µm wavelength range are theoretically discussed. It is clarified that the tolerance of the core radius and refractive index difference satisfying this dispersion conditions are 0.05µm and 0.01%. Bend-optimized W-type fibers are designed so as to minimize the bending sensitivity. It is also clarified that the allowable bending radius is reduced to less than 4 cm for the W-type fibers with a mode field diameter of 7µm.

Loss increase due to hydroxyl group formation of a fiber expose to hydrogen gas in measured. Experimental result shows that the loss increase is proportional to 0.57 power of exposure time. Temperature dependence of the loss increase is also estimated from the result.