How to choose an optic fiber

It is possible to buy a fiber-optic cable of the desired model only taking into account numerous conditions: application, installation, signal specifications. To select the product that meets the specific conditions, engineering calculations are necessary, and the laying of fiber-optic lines always precedes the project.
Regardless of what purpose you need to buy a fiber optic cable for the Internet, telephone line, or telemetry data transmission, the choice should always be coordinated with the design documentation.

It should be borne in mind that the calculation of the line and the installation of optical fiber requires special knowledge, skills, and tools, therefore, when buying a cable, specialist consultation is necessary.

Cable selection based on network type
Currently, optical cables (OK) are used on all communication networks:

  • International
  • Long distance
  • Urban
  • Rural
  • Subscriber
  • Local etc.

Therefore, its transmission parameters, reliability, and cost indicators should correspond to the type of network and the equipment used for information transmission systems.

Access network
So, for example, on transport networks (interoffice), where information flows between communication nodes (CS) are transmitted, the large broadband and reliability of the cable network is important. And on access networks associated with the provision of information to subscribers (cable TV networks, optical Ethernet, passive optical networks (PON), etc.), cost-effectiveness, flexibility, small dimensions and weight, protection against accidental damage, ease of installation and other factors are important.

In the future, we will pay more attention to optical cables for access networks, as they use more varieties of cables, and the design and installation are often carried out by specialists of various technical specialties.

The choice of optical cable design is mainly determined by the network section on which it will be used, as well as the conditions for its placement (in cable ducts, suspension on supports, indoors, etc.).

Many models of optical conductors can be divided into several groups according to the following criteria:

  • the number of modes transmitted along one thread;
  • the method of application and installation;
  • the number of fibers.

The quality of the fibers in the optical cable
Depending on the required number of optical fibers, the following types of cables are used:

  • FTTH - 1-2-4 optical fibers;
  • UT - from 4 to 8 optical fibers, 8 - 12 (possibly 12-24-48);
  • LT - 12-24, more than 24 (possibly 8-12).

Optical fibers are also divided into multimode (MM) and single-mode (SM), which differ from each other by the diameter of the light guide core. The names of these optical fibers were determined by the way in which the radiation propagates in them. The fiber consists of a core and a sheath with different refractive indices. The diameter of the light-conducting core of a single-mode fiber is about 8-10 microns, which is equal to the length of the light wave. With such a geometric parameter, only 1 beam can propagate inside the fiber (one mode). The size of the light guide conductor of a multimode optical fiber is about 50-60 μm, which allows a significant number of rays to propagate (many modes).

Quantitative indicators of fibers directly affect the conductivity and geometry of the proposed network. For example, a single fiber can both receive and transmit data. It is also possible to exchange data using 2 different optical fibers. Depending on the location of the network, the following types of cables are used: on the trunk span — it is advisable to use a cable with 24 or more optical fibers, on the distribution - enough for eight, and on the subscriber - often use a cable with one, two, four optical fibers.

An important point is the availability of fiber stock. In most cases, this stock is indicated for each specific situation. But, we can summarize it this way: for trunk sections, this is from 30% to 50% of the number of optical fibers involved; for distribution - from 15% to 20%; for subscribers, such a reserve, as a rule, does not matter, and therefore is not provided.

At the installation site, the cable is distinguished between internal and external. Since the conductor for external use can also be used indoors, it is sometimes also called universal.

Fiber count
The price of fiber is determined by the combination of the above parameters, including fiber material, type of booking, functionality, and other characteristics. Also, the manufacturer’s brand affects the cost of fiber optic cable.

The choice of the number of fibers
The number of fibers in the OK is determined by the number of transceiver nodes of the active equipment (both station and subscriber), as well as the network diagram. For example, the reception and transmission of signals can be organized both in two different fibers, and in one (for example, in PON), and when creating a broadcast network (broadcast), only one fiber is used for unidirectional transmission.

Do not forget about the supply of fibers in the cable for the subsequent development of the network. The amount of fiber stock depends on the network section. For example, on the backbone sections of access networks (PON, optical Ethernet, KTV), the stock, depending on the required number of fibers, can be 20-50%, on the distribution - 10-20%. And on subscriber sites of small length, the stock is not provided at all, since it is easy to report a new low-fiber cable there. The margin may also depend on the network topology ("star", "tree", "bus", etc.). Thus, the number of fibers in the cable in each section should be determined by the specific network design.

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