Enterprise Design Guide - Public - CommScope

Loose Tube Fiber Optic Cable Construction
Fiber cable starts with optical fiber. Optical fiber consists of a germanium doped silica core
within a concentric layer of silica cladding that is 125 µm in diameter. The core and cladding
are covered by two or three concentric layers of acrylate coatings which provide physical
protection. The outer acrylate layer is typically colored for identification. The coated fiber
diameter is approximately 250 µm.
Loose tube construction places several fibers in a small-diameter plastic buffer tube. Multiple
buffer tubes can be cabled together around a central strength member for higher fiber-count
cables. High-strength yarn is placed over the buffer tubes, and a jacket is applied. A variant of
loose tube design is called central tube that uses a single large diameter tube to contain all the
fibers.
Loose tube designs have lower attenuation than tight buffered cables and are usually used
for longer distance single-mode cables. Loose tube cables offer optimum performance in
campus subsystems. Loose tube design also helps fiber performance in areas with extremes of
temperature.
Indoor/outdoor cables
Indoor/outdoor cables are NEC listed (and sometimes LSZH) cables that meet environmental
requirements for outdoor usage. Indoor/outdoor cables can operate as underground or aerial
links between buildings without a transition to a listed indoor cable. They are protected against
moisture like outside plant cables (see below).
Outside plant
Outside plant cables are designed specifically for outdoor usage. They do not carry NEC
listings and are not intended for indoor use except when placed in rigid or intermediate metal
conduit (check local codes). Outdoor cables come in specialized constructions (armored,
multiple jackets, special chemical-resistant jacket compounds) to help them withstand severe
environments such as heat/cold, sunlight, petrochemical exposure and rodent attack.
Moisture ingress is addressed with either a water-blocking material in the buffer tubes, or with
water-swellable tapes and binding threads that incorporate super-absorbent polymers (SAPs).
These cables are intended for single-pass installation, whereas other aerial cables first require
installation of a supporting messenger wire and subsequent overlashed installation of the fiber
optic cable.
Self-supporting cables
Self-supporting cables are outdoor cables intended for aerial installation. They may have either
steel or non-metallic (dielectric) strength members incorporated into their jackets. Depending on
cable weight, messengered (figure-8 style) cables can span 400 meters (1312 feet) or longer.
Drop cables
Drop cables have low fiber counts (1 or 2 fibers) and are intended for short aerial, buried or
duct installations. They are small in diameter and have less tensile strength than normal selfsupporting
cables.
Optical fiber
cross section
Core
Cladding
Acrylate coatings
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