Understanding fiber optics jeff hecht pdf download cables are used mainly for digital audio connections between devices. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
Several layers of protective sheathing, depending on the application, are added to form the cable. Investigating a fault in a fiber cable junction box. The individual fiber cable strands within the junction box are visible. For use in more strenuous environments, a much more robust cable construction is required. This protects the fiber from tension during laying and due to temperature changes.
Loose-tube fiber may be “dry block” or gel-filled. Dry block offers less protection to the fibers than gel-filled, but costs considerably less. Instead of a loose tube, the fiber may be embedded in a heavy polymer jacket, commonly called “tight buffer” construction. 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber.
Distribution cables have an overall Kevlar wrapping, a ripcord, and a 900 micrometer buffer coating surrounding each fiber. A critical concern in outdoor cabling is to protect the fiber from contamination by water. This is accomplished by use of solid barriers such as copper tubes, and water-repellent jelly or water-absorbing powder surrounding the fiber. Finally, the cable may be armored to protect it from environmental hazards, such as construction work or gnawing animals. Modern fiber cables can contain up to a thousand fibers in a single cable, with potential bandwidth in the terabytes per second.
In some cases, only a small fraction of the fibers in a cable may be actually “lit”. Companies can lease or sell the unused fiber to other providers who are looking for service in or through an area. They may also deliberately under-invest to prevent their rivals from profiting from their investment. The highest strand-count singlemode fiber cable commonly manufactured is the 864-count, consisting of 36 ribbons each containing 24 strands of fiber. Optical fibers are very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions.
There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues, and zero-stress aging. The jacket material is application specific. The material determines the mechanical robustness, aging due to UV radiation, oil resistance, etc. Nowadays PVC is being replaced by halogen free alternatives, mainly driven by more stringent regulations. There are two main types of material used for optical fibers: glass and plastic. They offer widely different characteristics and find uses in very different applications. The buffer or jacket on patchcords is often color-coded to indicate the type of fiber used.
The strain relief “boot” that protects the fiber from bending at a connector is color-coded to indicate the type of connection. Sometimes used to connect external pump lasers or Raman pumps. Remark: It is also possible that a small part of a connector is additionally color-coded, e. E-2000 connector or a frame of an adapter. This additional colour coding indicates the correct port for a patchcord, if many patchcords are installed at one point. Individual fibers in a multi-fiber cable are often distinguished from one another by color-coded jackets or buffers on each fiber. TIA-598, “Optical Fiber Cable Color Coding.
TIA-598 defines identification schemes for fibers, buffered fibers, fiber units, and groups of fiber units within outside plant and premises optical fiber cables. This standard allows for fiber units to be identified by means of a printed legend. This method can be used for identification of fiber ribbons and fiber subunits. The legend will contain a corresponding printed numerical position number or color for use in identification. The colour code used above resembles PE copper cables used in standard telephone wiring. In the UK the colour codes for COF200 and 201 are different.
The cable elements start with the red tube and are counted around the cable to the green tube. 276 fibres or 23 elements for external cable and 144 fibres or 12 elements for internal. The cable has a central strength member normally made from fiberglass or plastic. There is also a copper conductor in external cables. 5 microseconds of latency per km. Thus the round-trip delay time for 1000 km is around 11 milliseconds. Very high quality singlemode fiber intended for long distance applications is specified at a loss of 0.