Fiber optic cable provides protection for the fibers from the environment encountered in an installation. Outdoor Cables is designed strong to protect the fibers to operate safely in complicated outdoor environment, it can be buried directly, pulled in conduit, strung aerially or even placed underwater. While indoor cables don’t have to be that strong.
Outdoor fiber optic cable is composed of many fibers enclosed in protective coverings and strength members. Common features for fiber optic cable include polarization maintaining, graded index, and metalization. Most outdoor fiber cables are loose buffer design, with the strengthen member in the middle of the whole cable, the loose tubes surround the central strength member. Inside the loose tube there is waterproof gel filled, whole cable materials used and gels inside cable between the different components will help make the whole cable resist of water.
Typical outdoor fiber optic cable types are used for aerial, direct buried and duct applications.
Loose Tube Cables
Loose Tube cables are the most widely used cables for outside plant trunks, as it can be made with the loose tubes filled with gel or water absorbent powder to prevent harm to the fibers from water. Loose Tube Fiber Optic cables are composed of several fibers together inside a small plastic tube, which are in turn wound around a central strength member and jacketed, providing a small, high fiber count cable. They can be installed in ducts, direct buried and aerial/lashed installations for trunk and fiber to the premise applications. Loose tube cables with singlemode fibers are generally terminated by spicing pigtails onto the fibers and protecting them in a splice closure. Multimode loose tube cables can be terminated directly by installing a breakout kit, also called a furcation or fan-out kit, which sleeves each fiber for protection.
Ribbon cable is preferred where high fiber counts and small diameter cables are needed. This cable has the highest packing density, since all the fibers are laid out in rows in ribbons, typically of 12 fibers, and the ribbons are laid on top of each other. Not only is this the smallest cable for the most number of fibers, it’s usually the lowest cost. Typically 144 fibers in ribbons only has a cross section of about 1/4 inch or 6 mm and the jacket is only 13 mm or 1/2 inch diameter! Some cable designs use a “slotted core” with up to 6 of these 144 fiber ribbon assemblies for 864 fibers in one cable! Since it’s outside plant cable, it’s gel-filled for water blocking or dry water-blocked. These cables are common in LAN backbones and data centers.
Armored Fiber Optic Cable
Armored cable is used in direct buried outside plant applications where a rugged cable is needed and/or for rodent resistance. Armored cable withstands crush loads well, for example in rocky soil, often necessary for direct burial applications. Cable installed by direct burial in areas where rodents are a problem usually have metal armoring between two jackets to prevent rodent penetration. Another application for armored fiber optic cable is in data centers, where cables are installed under the floor and one worries about the fiber cable being crushed. This means the cable is conductive, so it must be grounded properly.
Aerial Fiber Optic Cable
Aerial cables are for outside installation on poles. They can be lashed to a messenger or another cable (common in CATV) or have metal or aramid strength members to make them self supporting. A widely used Aerial Cable is optical power ground wire (OPGW) which is a high voltage distribution cable with fiber in the center. The fiber is not affected by the electrical fields and the utility installing it gets fibers for grid management and communications. This cable is usually installed on the top of high voltage towers but brought to ground level for splicing or termination.
Fiber Optic Indoor/Outdoor Cables are designed to meet both the stringent environmental requirements typical of outside plant cable AND the flammability requirements of premise applications. Ideal for applications that span indoor and outdoor environments. By eliminating the need for outside to inside cross-connection, the entire system reliability is improved and with lower overall installation costs.
Underwater and Submarine Cables
It is often necessary to install fibers under water, such as crossing a river or lake where a bridge other above water location is not possible. For simple applications a rugged direct burial cable may be adequate. For true undersea applications, cables are extremely rugged, with fibers in the middle of the cable inside stainless steel tubes and the outside coated with many layers of steel strength members and conductors for powering repeaters. Submarine cables are completed on shore, then loaded on ships and laid from the ship, often while operational to ensure proper operation.