Application of optical fiber transmission system in security engineering

Due to the short transmission distance of the monitoring cable, we recommend that the network cable in network monitoring should not exceed 90 meters. Even if the 75-5 commonly used in analog monitoring is used, we also recommend that it should not exceed 500 meters. Therefore, for long-distance monitoring, it is necessary to use Optical fiber transmission mode, then briefly introduce the application of optical fiber in video surveillance engineering from the following points.

Fiber Type

Optical cables are divided into indoor optical cables, outdoor optical cables, branch optical cables, and distribution optical cables according to different use 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 fiber: An optical fiber that transmits only one mode of optical signal. It is generally classified into G.652, G.653, G.654, G.655 and other transmission grades. Single-mode fiber can transmit 100M signals over a distance of several tens of kilometers. Multimode fiber: The fiber that can transmit multiple modes of optical signals is G.651 grade. According to the optical mode, it is divided into OM1, OM2, OM3. Multimode fiber transmits 100M signals with a maximum transmission distance of 2 kilometers.

Fiber laying method:

Conventional outdoor optical cables use the loose tube as the core container, which is the most common optical fiber core laying method.

Indoor optical cables are often laid in tight sleeves.

The fiber cores of the large-core-count fiber optic cables are also combined and laid in a ribbon-like manner.

Security fiber optic transmission system

Optical cable structure:

1. The most common optical cable structure is the layered optical cable. The optical cable with more than 12 cores is generally this structure. The optical cable cavity can accommodate multiple loose tubes. The loose tube is the basic unit. Each loose tube can accommodate 6 -12-core fiber core; the stranded cable is the central strength member, and the loose tube surrounds the central strength member.

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 stranded fiber optic cable is generally within 12, so the number of cores of the stranded fiber optic cable is generally from 12 cores to 144 core.

2. The structure of the outdoor optical cable below 12 cores is generally the central bundle type. This type of optical cable contains a central loose tube, which can contain 1-12 cores, and the outer sheath contains two parallel steel wires.

3. Ribbon optical cable, also known as skeleton slot 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 the pigtail, and the pigtail is to connect the optical fiber transceiver, the optical fiber switch or the optical terminal.

Optical fiber terminal box (splicing box or splice tray): The optical fiber splicing box is to splicing two optical fibers together.

Pigtail: One end of the fiber pigtail is spliced ​​with the optical fiber, and the other end is connected to the optical transceiver or optical switch and other equipment.

ODF optical fiber distribution frame and optical coupler: In some large and medium-sized monitoring projects, ODF optical fiber distribution frame and optical coupler and other equipment may be used. ODF optical fiber distribution frame is mainly used in computer rooms, which can make many optical fibers more regular , easy to maintain.

Optical fiber transceiver: also known as photoelectric converter, a device that converts optical port and electrical port, used in pairs, the electrical port is connected to the switch, and the optical port is connected to the fiber pigtail.

Optical fiber module: The optical fiber module is mainly used in the optical fiber switch. The optical fiber pigtail can be directly connected to the switch through the optical fiber module, eliminating the need for the optical fiber transceiver, but the price of the optical fiber switch 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 necessary to determine the fiber optic transceiver or fiber optic switch used first. The interface type, otherwise it cannot be inserted.

Fill Type:

Since the fiber core is fragile and easily broken, 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, filling the ointment in the optical cable cavity to achieve the effect of blocking water and protecting the fiber core.

2. Dry water blocking structure

3. Outer structure of inflatable structure optical cable: The shape features include flat optical cable, elliptical optical cable, self-supporting optical cable, and the conventional structure is circular

Fiber optic cable outer sheath: flame retardant structure, that is, the conventional PE/PVC outer sheath is added with flame retardant fuel to achieve flame retardant effect

Optical fiber knowledge

1. The tensile strength of optical fiber is very high, close to the tensile strength of metal

2. The ductility of fiber ( 1%) is worse than that of metal ( 20%)

3. When there are cracks, bubbles or debris in the 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. Losses increase with decreasing temperature at low temperatures

6. The optical fiber needs to strengthen the protection of mechanical properties, and needs to be protected from water to ensure the transmission performance

Wavelength: The communication window of optical signal of optical fiber communication, among which 850, 1310nm are multi-mode 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, the signal is only received but not sent or only sent but not received. One-way communication is understood as only receiving optical signals or only sending optical signals on a core fiber.

Duplex: both receive and transmit signals, divided into half-duplex and full-duplex, half-duplex can be understood as a core optical core, after receiving the signal, the signal can be sent and feedback through the same core optical fiber, but at this time only Can send or receive signals; and full-duplex still uses a core fiber, which can continuously send signals while receiving signals, and the two types of communication do not interfere with each other, generally through frequency division multiplexing, time division multiplexing, wave multiplexing 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, a professional fusion splicer is required, and the fusion splicing loss is not more than 0.03db, otherwise it will affect the bandwidth of the signal. In addition to the hot-melt method, there is also a cold splicing method. The optical fiber and the pigtail are connected together through the cold splicing of the optical fiber. However, the cold splicing is not as stable as the hot-melting method, and it is prone to problems after a long time. It is not recommended.

Optical fiber transmission characteristics

The transmission distance is long, the single-mode fiber can transmit 100M signals up to tens of kilometers, and the transmission of gigabit signals can also reach 5 kilometers. And the use of optical fiber long-distance transmission signal fidelity and picture clarity will not be affected.

Optical fiber is not subject to electromagnetic, strong electricity and other interference in the transmission process, and has strong anti-interference ability.

The bandwidth of optical fiber is theoretically unlimited, so one optical fiber with hundreds of cameras can fully guarantee the bandwidth. Therefore, the appropriate optical fiber transceiver should be selected according to the number of signal channels transmitted by the optical fiber. If there are less than 10 monitoring points , you can choose a 100M fiber transceiver, if there are more than 10 monitoring points, you need to choose a gigabit fiber transceiver.

The optical fiber can be laid in the ground or in the overhead. When installing overhead, try to ensure that the height is 6-7 meters. It is recommended to dig a trench deeper than 50cm when buried.

During the wiring process, try to avoid too large a bending angle of the optical fiber. If a sleeve is required, a plastic hose can be used.