Optical subscriber loops by nonpressurized optical fiber cable

Abstract

In optical‐fiber‐cable networks of Japan, usually dry air is compressed into the cable and joints and gas‐pressure sensors are used for remote‐supervision of pressure maintenance. However, optical fibers are different from metallic lines and penetrating water is not a direct obstacle. Further, the manufacture of gas dams is not as easy as that of the metallic cables, and the gas dams become very large in size so that it becomes difficult to put them in the line. Therefore, the nonpressurized cables with reliabilities as high as those of the pressurized ones have been investigated. This paper discusses first the main factors responsible for the reliability deterioration of nonpressurized optical fiber cables and joints, which are the important elements of an optical system. Then, as the nonpressurized line structure, the waterproof optical fiber cables and the remote supervision of joints are discussed. Using a simple remote‐supervisory structure which consisted of the water sensors and OTDR, it is shown that the realization of reliabilities as high as those of the pressurized cables is possible.