In loose-tube construction the fiber is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fiber itself. This protects the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be dry block or gel-filled.OverviewA fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an but containing one or more that are used to carry light. The optical fiber elements are typically individually. Optical fiber consists of a and a layer, selected for due to the difference in the between the two. In practical fibers, the cladding is usually coated wit.