82
2 Optical Fiber Structures and Light Guiding Principles
encapsulated within its own 900 μm diameter plastic buffer structure, hence the designation tight-buffered design. The 900 μm buffer is nearly four times the diameter and
five times the thickness of the 250 μm protective coating material. This construction feature contributes to the excellent moisture and temperature performance of
tight-buffered cables and also permits their direct termination with connectors. In a
single-fiber module, a layer of amarid strength material surrounds the 900 μm fiber
structure. This configuration then is encapsulated within a polyvinyl chloride (PVC)
outer jacket.
In the loose-tube cable configuration one or more standard-coated fibers are
enclosed in a thermoplastic tube that has an inner diameter much larger than the fiber
diameter. The fibers in the tube are slightly longer than the cable itself. The purpose
of this construction is to isolate the fiber from any stretching of the surrounding cable
structure caused by factors such as temperature changes, wind forces, or ice loading.
The tube is filled with either a gel or a dry water-blocking material that acts as a
buffer, enables the fibers to move freely within the tube, and prevents moisture from
entering the tube. A loose-tube cable typically has a steel armoring layer just inside
the jacket to offer crush resistance and protection against gnawing rodents. Such a
cable can be used for direct burial or aerial-based outside plant applications.
To facilitate the field operation of splicing cables that contain a large number of
fibers, cable designers devised the fiber-ribbon structure. As shown in Fig. 2.30, the
ribbon cable is an arrangement of fibers that are aligned precisely next to each other
and then are encapsulated in a plastic buffer or jacket to form a long continuous
ribbon. The number of fibers in a ribbon typically ranges from four to twelve. These
ribbons can be stacked on top of each other to form a densely packed arrangement
of many fibers (e.g., 144 fibers) within a cable structure.
There are many different ways in which to arrange fibers inside a cable. The
particular arrangement of fibers and the cable design itself need to take into account
issues such as the physical environment, the services that the optical link will provide,
and any anticipated maintenance and repair that may be needed.
Fig. 2.30 Example of the
layered ribbon structure of a
64-fiber cable module
Armored outer
jacket
8 x8 fiber
ribbon structure
2 Optical Fiber Structures and Light Guiding Principles
encapsulated within its own 900 μm diameter plastic buffer structure, hence the designation tight-buffered design. The 900 μm buffer is nearly four times the diameter and
five times the thickness of the 250 μm protective coating material. This construction feature contributes to the excellent moisture and temperature performance of
tight-buffered cables and also permits their direct termination with connectors. In a
single-fiber module, a layer of amarid strength material surrounds the 900 μm fiber
structure. This configuration then is encapsulated within a polyvinyl chloride (PVC)
outer jacket.
In the loose-tube cable configuration one or more standard-coated fibers are
enclosed in a thermoplastic tube that has an inner diameter much larger than the fiber
diameter. The fibers in the tube are slightly longer than the cable itself. The purpose
of this construction is to isolate the fiber from any stretching of the surrounding cable
structure caused by factors such as temperature changes, wind forces, or ice loading.
The tube is filled with either a gel or a dry water-blocking material that acts as a
buffer, enables the fibers to move freely within the tube, and prevents moisture from
entering the tube. A loose-tube cable typically has a steel armoring layer just inside
the jacket to offer crush resistance and protection against gnawing rodents. Such a
cable can be used for direct burial or aerial-based outside plant applications.
To facilitate the field operation of splicing cables that contain a large number of
fibers, cable designers devised the fiber-ribbon structure. As shown in Fig. 2.30, the
ribbon cable is an arrangement of fibers that are aligned precisely next to each other
and then are encapsulated in a plastic buffer or jacket to form a long continuous
ribbon. The number of fibers in a ribbon typically ranges from four to twelve. These
ribbons can be stacked on top of each other to form a densely packed arrangement
of many fibers (e.g., 144 fibers) within a cable structure.
There are many different ways in which to arrange fibers inside a cable. The
particular arrangement of fibers and the cable design itself need to take into account
issues such as the physical environment, the services that the optical link will provide,
and any anticipated maintenance and repair that may be needed.
Fig. 2.30 Example of the
layered ribbon structure of a
64-fiber cable module
Armored outer
jacket
8 x8 fiber
ribbon structure