Shinzo Yamakawa

High-modulus low-linear-expansion-coefficient loose-jacket optical fibers

Optical fibers loosely jacketed with high-modulus low-linear-expansion-coefficient polymers have been proposed, and the mechanical, thermal, and optical properties have been investigated. The loose-jacket tube is made of highly oriented polyoxymethylene (POM), which is produced by tensile-drawing the isotropic POM tube with dielectric heating. The oriented POM exhibits Youngs moduli 20-40 GPa and linear expansion coefficients of the order of 10^{-5}-10^{-6}\deg C-1. Owing to the low linear expansion coefficients of the material, the oriented POM loose-jacket optical fiber has no low-temperature excess losses, which is due to fiber bends caused by thermal contraction of the loose tube, in the -60-80\deg C temperature range.

Slip mechanism in optical fiber coating with open-cup applicators

The allowable maximum coating speed of optical fibers has been correlated to the flow properties of the coating material itself. The maximum smooth coating speed has been measured from the coating thickness fluctuation-coating speed curves using several types of silicone resins. Flow curves of the silicone resins also have been measured by two different viscometers, i.e., cone-plate and capillary viscometers. The maximum smooth coating speed, at which the coating thickness fluctuation begins to increase, has been found to correspond to the critical shear rate at which the flow curve deviates from a power law. This correspondence probably results from the fact that the slip occurs both at the fiber-coating material interface and at the viscometer (cone, plate, or capillary)-coating material interface. Accordingly, the maximum smooth coating speed can be predicted from the critical shear rate value without the actual fiber coating experiments.