Fiber Optic Cable Construction

In any detailed discussion of how to deal with fiber optic cable, some fibers are discussed briefly and cable design is required. Eliminating confusion of different terms, and to provide an 
understanding of cable construction will make handling the products less complicated.

Fiber

The cable cross section is two fiber cables for interconnect applications. The construction of the glass can be looked at separately from the design of the cable, as the fiber itself is constructed using distinct materials and is shipped by the fiber manufacturer as a finished product. FiberStore takes the coated optical fiber and incorporates it into a multitude of finished cable products.

All of the glass fiber used by FiberStore is manufactured using the same basic construction. Two layers of glass are covered by a protective coating, the fiber’s core and cladding are both made of silica glass. It is these two layers that propagate the light signal and determine the performance of the fiber. A slight difference in optical characteristics between these layers keeps the signal within the core region. The glass is protected by a dual layer of ultra-violet-cured acrylate material.The coating protects the surface of the glass from abrasion during normal routine handling, there by ensuring the glass maintains it’s high tensile strength. The acrylate coating, which also functions optically by stripping out any light which might enter the cladding region, isremoved for termination and splicing.

Buffer Types

All of FiberStore fiber optic cables fall into one of two categories: tight buffered or loose tube buffered. The two cable buffer styles exhibit different optical, mechanical, and costcharacteristics. Originally, loose tube cable constructions were developed for long haul telephony applications which required a rugged, low cost, high fiber count outside plant cable solution. In a premises wiring plan this cable type is often used between buildings, although recent developments in cable design have produced loose tube cable for indoor/outdoor applications (know indoor outdoor cable). The tight buffer cable construction was developed for both indoor and outdoor premises wiring applications. Most of FiberStore’s tight buffer cables are rugged enough for many inter building applications while offering the tight buffer design advantages of ease of terminations, meeting NEC flammability codes, and cable flexibility.

Tight Buffered Fiber

A thermoplastic material is extruded directly over the acrylate coating, increasing the outside diameter of the fiber to 900 micros (0.9 mm), an industry standard. The tight buffer supplies the fiber with added mechanical and environmental protection, increased size for easy handling, and a simple means of adding color coding for fiber identification. During connectorization, the buffer is stripped back to an exact length as required by the connector manufacturer.

Loose Buffered Fiber

In loose tube cable, the coated fiber “floats” within a rugged, abrasion resistant, oversized tube which is filled with optical gel. Since the tube does not have direct contact with the fiber, any cable material expansion or contraction will not cause stress on the fiber. Much of the external stress placed on the tube also will not be transferred to the fiber. The non-hygroscopic gel prevents water from entering the tube.

Strength Members

FiberStore optical fiber cable designs utilize aramid yarn as the primary strength member. Some designs also use a fiberglass central strength member. Both of these materials serve as the load bearing members of an optical fiber cable during installation. In many cables the aramid also acts as a strength member during termination.

Core Wrap and Ripcords

Core wraps and ripcords are designed to make removal of the exterior cable sheath easier, preventing unnecessary stress to the core. The non-hygroscopic core wrap creates a barrier between the core and the jacket, preventing adhesion and facilitating jacket removal. Ripcords provide a means of stripping back the jacket without the use of invasive tools which could harm the cable core and damage fibers.

Outer Jacket

The true cable jacket is usually the outermost element in the cable design. It serves to protect the cable against environmental hazards and gives the installer a mean of managing the cable. Without the outer jacket, in many designs the buffered fibers would have only the aramid wrap to cover them. Typical jacket materials include Polyvinylchloride (PVC), Polyethylene (PE) or Polyvinylidene Fluoride (PVDF). Also, without selectively choosing the appropriate jacket material most cables would be entirely incapable of passing a flame test. Outer jackets are always stripped back to expose the fibers at the point of termination or connectorization.

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