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. There are usually G.652, G.653, G.654, G.655 and other transmission grade classifications.
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.
Fiber Applications
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 optical cable is the central reinforcing member, and the loose tube surrounds the central reinforcing core. For practical application, the fiber core needs to be covered with different colors, a total of 12 colors, while the loose stranded optical cable is covered with different colors. The number of sleeves is generally within 12, so the number of cores of the stranded optical cable is generally from 12 cores to 144 cores.
2. The structure generally used for outdoor optical cables below 12 cores is the central tube 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.
Optical fiber knowledge
1. The tensile strength of optical fiber is very high, close to the tensile strength of metal;
2. The ductility of optical 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 rainwater of the optical fiber is easy to break, and the cutting loss is greatly increased;
5. The loss increases with decreasing temperature at low temperature;
6. The optical fiber needs to strengthen the protection of mechanical properties, and needs to carry out waterproof protection 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, 1640 nm, 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 one core fiber.
Duplex: both receive and send 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 fiber, but at this time only The signal can be sent but cannot be received; while full-duplex still uses a single core fiber, it can continuously send signals while receiving signals, and the two types of communication do not interfere with each other. Generally, frequency division multiplexing, time division multiplexing and wave multiplexing to achieve.
