When reading an article or when talking with someone about fiber optics it is important to know what fiber optic they are referring to. Not all fiber optic cables are the same. In this book we will focus on the optical fiber used in communications; however, it can also be used in lighting, in medical controls, in non-destructive tests and in the manufacture of sensors for physical measurements.
In the field of communications, there is the optical fiber for "external plant", which is used for telephone networks, cable television (CATV), metropolitan networks, services, etc., and the fiber used for the internal plant, that is, the one found in buildings and in various facilities. In the same way that "cable" can have many meanings - the optical fiber that is used for electric power, security, ventilation, heating and air conditioning (HVAC), closed-circuit television (CCTV), Local area networks (LAN) or telephony is not the same, which can generate great confusion for the beginner. Let's define some terms.
External plant
Telephone, cable television, and internet companies use fiber optic, which is almost entirely outside buildings and referred to as an external plant (OSP), as it hangs from poles, it is underground, it goes through underground ducts or it can even be submerged underwater. Most cross long distances, ranging from a few meters to a few hundred kilometers.
Generally, the cables of the external plant have a very high amount of fibers, up to 288 or more. Cable designs have been optimized according to your application: duct cables are optimized to be tensile and resistant to moisture; underground cables are optimized to resist moisture and rodent damage; the aerial cables are in front of the continuous traction and extreme weather conditions, and submarine cables are optimized to resist moisture penetration. The installation requires special equipment, such as cable handles, and even trailers to transport huge cable reels.
The long distances involve spliced cables since the cables are not made of lengths greater than 4-5 km. (2.5 - 3 miles), and most splices are made by fusion splices. Connectors (usually SC or LC) are spliced at the end of the cable, turning them into connectorized fiber cables ( pigtails). After installation, all fibers and splices are tested with an OTDR (optical reflectometer in the time domain).
If this seems costly, you're right! Generally, the installer has a temperature-controlled vehicle, be it a truck, a trailer and/or a truck with a crane. Investing in fiber optic fusers, OTDR and other equipment can be quite expensive. Most of the telephony facilities in the external plant are carried out by the same telephone companies, while a small number of a large number of specialized installers perform cable television installation, public and municipal services.
Wiring in the internal plant
On the contrary, the wiring in the internal plant (wiring in buildings and other facilities) implies shorter distances, rarely greater than a few hundred meters, generally with less fiber per cable. Mostly multimode fiber is used, except in the case of the informed user who installs hybrid cable with multimode fiber and single-mode for future high bandwidth applications.
Practically no fusion splices are used in these types of facilities. The cables for the connection between buildings can be double-coated, one of polyethylene for the external plant over another of PVC, for installations in buildings that require cable coverings with fire-retardant properties. Today, connectors generally have less loss than splices, and connection panels provide greater flexibility for movements, additions, and modifications.
The most used connectors are those of type SC or ST, and those of type LC are beginning to be more popular. The terminations are made by installing connectors directly at the ends of the fiber, mainly through the use of splicing techniques with pre-polished adhesives or connectors. The tests are performed with a source and a meter, but each installer should have an indicator for light flashes to verify the continuity of the fiber and the connection.
Unlike the technician working in the external plant, the cable installer working in the internal plant (which generally also installs the power cable and the cat. 5/6 cable for LAN networks) probably makes a relatively minor investment in tools and equipment. There are thousands of wiring installers that perform fiber optic work; They discovered that it is not "a science", and that their small initial investment in training, tools and testing equipment is recovering rapidly.
Installers
Not many installers perform both types of wiring: in external plant and in the internal plant. The companies that do it are generally large and have separate departments that perform each type of wiring with different personnel. Most contractors only perform wiring in the internal plant.
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