We have developed a promising method for suppressing moisture condensation that prevents insulation failures in surge protectors. By analyzing surge protectors retrieved from the field, we found that electrolytic corrosion had occurred due to the encroachment of sea salt, the application of bias voltages, and the condensation of moisture. To suppress moisture condensation, a key factor in insulation failure, we applied a previously developed humidity-control package containing water-absorbent polymer. We experimentally optimized the design and functionality of the polymer package. We found that sealing the feed-through apertures alone was not enough to suppress moisture inflow and that a relatively large amount of water-absorbent polymer was needed to prevent water condensation in environments with extremely high humidity for extended periods of time. Laboratory experiments and field tests demonstrated that our optimized package minimized humidity fluctuation and thus moisture condensation in surge protectors, thereby preventing insulation failure. Application of this method to installed surge protectors greatly reduced the insulation failure rate.

A low-loss dispersion-modified single-mode fiber with low dispersion in the 1.5µm wavelength region has been designed and fabricated by using VAD method. A minimum loss of 0.23 dB/km at 1.55 µm and a small dispersion slope less than 0.023 ps/km/nm2 have been achieved around the zero-dispersion wavelength. Moreover, for the fist time, the tolerance of the core radius has been estimated by waveguide dispersion measurement.

The longitudinal chromatic dispersion in single-mode fibers is investigated theoretically and experimentally. With a fabricated tapered fiber evaluation of longitudinal chromatic dispersion is clarified by using simple equation.

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.