Bare Fiber Optic Cable Design

Fiber optic cables are common in today’s telecommunication, but how much do you know their design.

From the fiber production process, the composition of the fiber from the inside out: the core, cladding, a coating, and secondary coating. The bare optical fiber means it has not been coated, only with fiber optic core and cladding. Optical signals in optical fibers are using light of the principle of total reflection. The glass fiber is the main channel of transmission of optical signals, the cladding is used to reflect the optical signal, and the coating is to protect the fragile core.

Bare glass fibers are based on silica or other glass materials. The glass surface is susceptible to abrasion and mechanical flaws. To protect the cable from the environment, the buffer coating or jacket fits over the core and cladding. The diameter ranges from 250μm to 900μm, usually 250um for single mode and multimode fibers, but 400um is also very common in polarization maintaining fibers. It provides mechanical protection while allowing for flexibility in the fiber. The buffer coating is usually made of a soft or hard plastic such as acrylic or nylon. Kevlar is a popular choice for the jacket material. It is strong and used to bundle and protect the loose tubes or fibers in the cable. Kevlar protects the fibers when the tension is placed on the cable. The color of this jacket typically depends on the type of fiber, single mode fibers typically wear a yellow jacket and multi-mode fibers wear an orange jacket.

A secondary buffer coating is then applied to the fibers to give protection against external mechanical and environmental factors. This layer may take different designs and its main function is to prevent micro-bending losses.

A. 900um tight buffer. A 900um diameter hard plastic material is coated as the secondary buffer layer. The material is usually Nylon, Hytrel or Tefzel and it provides stiffening for the fiber against outside microbending influences. With tight buffered single mode or multimode optical fiber secondary coating structure is named tight buffered cable. It is the basic components for the manufacture of a variety of indoor cable, which can also be used alone. The tight buffer fiber can be used directly in pigtail for the connection of various types of optical active or passive components, instruments and terminal equipment connections.

B. Loose tube. Another alternative approach to a direct tight buffer coating is to use a 900um loose tube. The 250um or 400um bare fiber is placed in an oversized loose tube in which the fiber is mechanically isolated from external forces. Then, coupled with strengthening the core which used to increase the fiber optic cable strength and the outer sheath, such as aluminum foil and polyethylene jacket, became a fiber optic cable.

C. Filled loose tube. The loose tube discussed above can be filled with moisture-resistant compound which provides mechanical protection and a water barrier layer around the fiber. This filling material is generally petroleum or silicone-based compounds.

There are many types fiber optics from various fiber optic cable manufacturers and you can have a look at FiberStore, who is professional in cables.