How to select the type and number of cores


Types of optical fibers

In today's HD surveillance camera system applications, optical fiber is one of the connections that can provide the best bandwidth performance. When using the optical fiber transmission system, the image quality of the system is only limited by the camera, the environment and the monitor, and the optical fiber transmission system can transmit the image to a very far place without any form of distortion of the signal, let alone without degrading the clarity or details of the image picture. It can be said that optical fiber transmission system is the lifeline of the whole monitoring system.


Optical fibers are classified into indoor optical fibers, outdoor optical fibers, branch optical fibers, and distribution optical fibers.


According to the laying mode, it can be divided into self-supporting overhead optical fiber, pipeline optical fiber, armored buried optical fiber and submarine optical fiber.


According to the fiber structure, it can be divided into beam tube fiber, layer-stranded fiber, skeleton fiber, hugging fiber, belt fiber, non-metallic fiber and branching fiber.


According to the purpose: long-distance communication optical fiber, short-distance outdoor optical fiber, hybrid optical fiber and building optical fiber;

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Optical fibers can be divided into single-mode and multi-mode according to the transmission mode. Single-mode optical fibers are generally used for monitoring.


Single-mode optical fiber: optical fiber that transmits only one mode optical signal. It is classified into G.652, G.653, G.654, G.655 and other transmission levels, and single-mode optical fiber can transmit 100-megabit signals over a distance of tens of kilometers. Single-mode fiber only transmits main mode, that is to say, light is transmitted only along the inner core of the fiber. Because mode dispersion is completely avoided, the transmission frequency band of single-mode fiber is very wide, so it is suitable for large-capacity and long-distance fiber communication. The optical wavelength of single-mode fiber is 1310nm or 1550nm.


Multi-mode optical fiber: an optical fiber capable of transmitting multiple modes of optical signals, of G.651 class, which is classified into OM1, OM2, and OM3 according to the optical mode. Multi-mode optical fiber can transmit 100-megabyte signals with a maximum transmission distance of 2km. Multi-mode fiber, in a certain operating wavelength, there are multiple modes in the fiber transmission, this fiber is called multi-mode fiber, due to dispersion or aberration, so the transmission performance of this fiber is poor, the frequency band is relatively narrow, the transmission capacity is relatively small, the distance is relatively short.


Fenite optical fiber

Optical fiber laying mode and requirements:


Conventional outdoor fiber is the container of the loose tube as the core, which is the most common way to lay the fiber core. The indoor optical fiber is usually laid tightly. The fiber core of large core number fiber can also be combined and laid in ribbon mode.


The bending radius of the optical fiber should be at least 15 times of the outer diameter of the optical fiber, and at least 20 times during construction. When deploying optical fibers, the rotation of the optical fiber disk should be synchronized with the routing speed. The index speed of the optical fiber is generally 15 meters per minute. When routing optical fibers, maintain a relaxed radian at the outlet of optical fibers and retain a buffer margin. Do not use too much to avoid backbuckles of optical fibers. The reserved length of optical fiber at both ends is 5-10 meters; When laying out optical fibers, label them and fill in the routing record. All optical fibers are not exposed.




The choice of light core


The number of cores is the number of glass fibers contained in each fiber. Here are some methods to determine the number of fiber cores.


First, know the number of wiring points at this layer, figure out the number of switches, and whether switches are stacked or not. If the core switches are stacked and redundant in dual-system hot backup mode, six cores are sufficient. (Two cores each use two cores in redundancy mode.) If a switch needs four cores without stacking, multiply the number of switches by four plus the redundancy of four cores. (Note: Redundancy: as long as there are more than used, the excess is called redundant: one is used, the other is exactly the same as the standby; Hot backup: both are working at the same time; Cold backup: The backup device is in standby state.)


Experience: Each floor wiring room (horizontal wiring cabinet), set an optical fiber, generally six core: two core use, two core standby, two core redundancy; There are also ones that use eight-core fiber. The minimum specification configuration is 2 cores per 48 points. Of course, four cores can be selected for 48 points, because two cores are the minimum unit of an optical fiber, so it is appropriate to leave two cores as a spare part.


The above is the number of fiber core to determine the method, you can understand. Backup can be selected because of people, so the number of fiber cores varies more, according to the specification only to ensure a minimum selection and a backup number of cores can be.


Pay attention to


The selection of optical fiber is not only based on the number of fiber cores and types of optical fibers, but also based on the use of optical fibers to select the outer sheath of the optical fiber. The following points should be paid attention to when selecting the optical fiber:


1. When outdoor optical fiber is directly buried, armored optical fiber should be selected. When overhead, two or more reinforcement black plastic outer sheath optical fiber can be selected.

2. When selecting optical fibers used in buildings, attention should be paid to the characteristics of flame retardant, poison and smoke. Generally, flame retardant and smoke type can be selected in pipelines and forced ventilation places


3. For vertical wiring in the building, laminated fiber can be selected; Horizontal wiring, optional branching fiber.


4. Multi-mode optical fiber can be selected for transmission distance within 2km; Over 2km, relay or single-mode fiber can be used.


The above is only from the application of several problems to consider, the implementation of the need to be flexible. In fact, wiring environment is complex and diverse, all kinds of problems may appear at any time, which requires us to strictly follow wiring standards when planning and construction, encounter problems, flexible analysis, will be satisfactorily solved.


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