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.

Common Bulk Fiber Optic Cables Description

Bulk fiber optic cables are widely used in modern, gradually replace of copper cables.

Key Specifications Of Fiber Optic Cables
  • Transmission rate of 100 Mbps;
  • Cable length of 2 kilometers or more;
  • Not affected by electrical interference;
  • Supports voice, video, and data;
  • Provides the most secure media;
  • Commonly used in backbones between buildings and Token Ring networks;
  • Specifications for fiber include the IEEE’s 10BaseFL (Ethernet) and ANSI’s
  • FDDI or Fiber Distributed Data Interface (Token Ring).

Depending on the number of fibers and how and where it will be installed, bulk fiber optic cables come in lots of different types. Choose cable carefully as the choice will affect how easy it is to install, splice or terminate and, most important, what it will cost! Such as tight buffered fiber cable and loose tube cable. Loose tube cable majority used in outside-plant installations, while tight-buffered cable primarily used inside buildings.

Tight Buffered Cable

Tight buffered (coated with a 900 micron buffer over the primary buffer coating) with Kevlar (aramid fiber) strength members and jacketed for indoor use. The jacket is usually 3mm (1/8 in.) diameter. Zipcord is simply two of these joined with a thin web. It’s used mostly for patch cord and backplane applications.

Single-mode tight-buffered cables are used as pigtails, patch cords or jumpers to terminate loose-tube cables directly into opto-electronic transmitters, receivers and other active and passive components. Multimode tight-buffered cables also are available and are used primarily for alternative routing and handling flexibility and ease within buildings.

Distribution Cables

Distribution Cables contain several tight-buffered fibers bundled under the same jacket with Kevlar strength members and sometimes fiberglass rod reinforcement to stiffen the cable and prevent kinking. These cables are small in size, and used for short, dry conduit runs, riser and plenum applications. The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a “breakout box” or terminated inside a patch panel or junction box. They can be multimode distribution indoor cable, single mode plenum distribution indoor cable, multimode plenum distribution indoor cable, waterproof cables, etc.

Loose Tube Cable

In a loose-tube cable design, color-coded plastic buffer tubes house and protect optical fibers. A gel filling compound impedes water penetration. Excess fiber length (relative to buffer tube length) insulates fibers from stresses of installation and environmental loading. Buffer tubes are stranded around a dielectric or steel central member, which serves as an anti-buckling element. The cable core, typically surrounded by aramid yarn, is the primary tensile strength member. The outer polyethylene jacket is extruded over the core. If armoring is required, a corrugated steel tape is formed around a single jacketed cable with an additional jacket extruded over the armor.

FiberStore covers a wide production line of bulk fiber optic cable, from common bare fiber, waterproof cables to special fiber cables for specific applications. Flexible or rigid cables of copper or aluminium, with a complete range of polymers and protectors, always developed under the most stringent international standards.