fiber type
Optical cables are divided into indoor optical cables, outdoor optical cables, branch optical cables, and distribution optical cables according to different usage occasions.
Optical fibers can be divided into single-mode and multi-mode according to the transmission mode, so monitoring generally uses single-mode optical fibers. Single-mode optical fiber: An optical fiber that only transmits one mode of optical signal. Conventionally, there are transmission grades such as G.652, G.653, G.654, and G.655. Single-mode optical fiber can transmit 100M signals over tens of kilometers. Multi-mode optical fiber: An optical fiber that can transmit multiple modes of optical signals. It is of G.651 grade. It is divided into OM1, OM2, and OM3 according to the optical mode. The longest transmission distance of 100M signals transmitted by multi-mode optical fiber is 2 kilometers.
Optical fiber laying method:
Conventional outdoor optical cables use loose tubes as core containers, which is the most common way of laying optical fiber cores.
Indoor optical cables are usually laid in a tight sleeve.
The core of the large-core optical cable is also combined in a ribbon form to lay the fiber core.
Security Optical Fiber Transmission System
Optical cable structure:
1. The most common optical cable structure is the layer-twisted optical cable, which is generally the structure of optical cables with more than 12 cores. The cavity of the optical cable can accommodate multiple loose tubes. With loose tubes as the basic unit, each loose tube can accommodate 6 -12-core fiber core; the layer-stranded optical cable is the central strength member, and the loose tube is wrapped around the central strength core.
For practical application, the fiber core needs to be covered with different colors, a total of 12 colors, and the number of loose tubes of the layer-stranded optical cable is generally within 12, so the number of cores of the layer-stranded optical cable generally ranges from 12 cores to 144 cores. core.
2. The structure of outdoor optical cables below 12 cores is generally a central bundle tube type. This type of optical cable contains a central loose tube inside.
The inner can contain 1-12 cores, and the outer sheath contains two parallel steel wires
3. Ribbon optical cable, also called skeleton groove structure, is generally used as an optical cable structure with a large number of cores
Optical Fiber Supporting Equipment
Optical fiber distribution frame (box): The optical fiber terminal box is to protect the optical fiber and pigtail, and the pigtail is to connect the optical fiber transceiver, optical fiber switch or optical transceiver.
Optical fiber terminal box (splicing box or splicing tray): The optical fiber splicing box is used to fuse two optical fibers together.
Pigtail: One end of the optical fiber pigtail is fused with the optical fiber, and the other end is connected to equipment such as optical fiber transceivers or optical fiber switches.
ODF optical fiber distribution frame and optical coupler: In some large and medium-sized monitoring projects, ODF optical fiber distribution frame and optical coupler may be used. ODF optical fiber distribution frame is mainly used in computer rooms, which can make many optical fibers more regular , easy maintenance.
Optical fiber transceiver: also known as a photoelectric converter, a device that converts optical ports and electrical ports, used in pairs, the electrical port is connected to the switch, and the optical port is connected to the optical fiber pigtail.
Optical fiber module: The optical fiber module is mainly used in optical fiber switches. The optical fiber pigtails can be directly connected to the switch through the optical fiber module, eliminating the need for optical fiber transceivers, but the price of optical fiber switches is relatively high.
Pigtail interface type
The commonly used interface types of pigtails are FC, ST, FC/APC, SC/APC, SC, etc. The commonly used interface on fiber optic transceivers is SC interface, so when selecting pigtails, it is first necessary to determine the fiber optic transceiver or fiber optic switch used interface type, otherwise it cannot be inserted.
Fill type:
Since the fiber core is fragile and easy to break, the fiber optic cable needs to be filled to protect the fiber core
1. The conventional outdoor optical cable filling structure is: ointment water-blocking structure, the ointment is filled in the optical cable cavity to achieve the functions of water-blocking and fiber core protection.
2. Dry water blocking structure
3. The outer structure of the inflatable optical cable: the appearance features include flat optical cable, elliptical optical cable, self-supporting optical cable, and the conventional structure is circular
Optical cable outer sheath: Flame retardant structure, that is, the conventional PE/PVC outer sheath is added with retardant fuel to achieve flame retardant effect
Optical fiber knowledge
1. The tensile strength of optical fiber is very high, close to that of metal
2. The ductility of optical fiber (1%) is worse than that of metal (20%)
3. When there are cracks, air bubbles or impurities in the optical fiber, it is easy to break under a certain tension.
4. The optical fiber is easily broken by rainwater, and the cutting loss is greatly increased
5. Loss increases with decreasing temperature at low temperature
6. The optical fiber needs enhanced mechanical performance protection and waterproof protection to ensure transmission performance
Wavelength: The communication window of the optical signal of optical fiber communication, among which 850, 1310nm are multimode optical fiber communication windows, which are short wavelength windows; 1310, 1550, 1640nm, etc. are single mode optical fiber communication windows, which are long wavelength windows.
Simplex: In communication, signals are only received but not sent or only sent but not received. One-way communication is understood as only receiving or sending optical signals on one core optical fiber.
Duplex: Both receive and send signals, divided into half-duplex and full-duplex, half-duplex can be understood as a single-core optical core, after receiving the signal, the signal can be sent and fed back through the same core optical fiber, but at this time only Can send but not receive signals; and full-duplex still uses one-core optical fiber, which can continuously send signals while receiving signals, and the two kinds of communication, receiving and sending, do not interfere with each other. Multiplexing is used to achieve.
Fiber splicing method
Optical fiber is the abbreviation of optical fiber, so the optical fiber connection can not be directly twisted together like copper wire, it needs a professional fusion splicer, and the fusion splicing loss is not greater than 0.03db, otherwise the bandwidth of the signal will be affected. In addition to the hot melt method, there is also a cold splicing method. The optical fiber is connected to the pigtail through the optical fiber cold splice, but the cold splice is not as stable as the hot melt, and it is prone to problems after a long time. It is not recommended to use it.
Optical fiber transmission characteristics
The transmission distance is relatively long. Single-mode optical fiber can transmit hundreds of megabit signals up to tens of kilometers, and gigabit signals can reach up to 5 kilometers. Moreover, the use of optical fiber for long-distance transmission of signal fidelity and picture clarity will not be affected.
The optical fiber is free from electromagnetic, strong electricity and other interference during the transmission process, and has strong anti-interference ability.
