What is an optical cable - Basic knowledge of optical cablesBasic knowledge of optical cables
I. Definition of optical cablesOptical fiber cable is mainly composed of optical fiber (optical fiber) and plastic protective sleeve and plastic outer skin. It is a communication line in which a certain number of optical fibers form a cable core in a certain way, and are covered with a sheath, and some are also covered with an outer sheath to realize the transmission of optical signals.
That is: a cable formed by optical fiber (optical transmission carrier) through a certain process.
II. Types of optical cablesThere are many types of optical cables, and there are more ways to classify them. There are different classifications according to different standards:
1. According to transmission performance, distance and purpose, it is divided into urban optical cables, long-distance optical cables, submarine optical cables and user optical cables.
2. According to the type of optical fiber, it is divided into single-mode optical cables and multi-mode optical cables.
3. According to the method of fiber sheathing, it can be divided into tight-buffered optical cable, loose-buffered optical cable, bundled optical cable and ribbon optical cable. 4. According to the number of optical fiber cores, it can be divided into single-core, dual-core, quad-core, and six-core optical cables. 5. According to the configuration method of reinforcement components, it can be divided into central reinforcement component optical cable (such as stranded optical cable, skeleton optical cable), dispersed reinforcement component optical cable (such as bundled tube reinforced optical cable and flat optical cable), sheath reinforcement component optical cable (such as bundled tube steel wire armored optical cable), and PE outer sheath with a certain number of fine steel wires. 6. According to the laying method, it can be divided into pipeline optical cable, direct buried optical cable, aerial optical cable and underwater optical cable. 7. According to the properties of the sheath material, it can be divided into polyethylene sheath ordinary optical cable, polyvinyl chloride sheath flame-retardant optical cable and nylon anti-ant and anti-rat optical cable. 8. According to the transmission conductor and medium conditions, it can be divided into metal-free optical cable, ordinary optical cable, and optoelectronic composite cable.
9. According to the structure, it can be divided into flat structure optical cable, layer-twisted structure optical cable, skeleton structure optical cable, armored structure optical cable (including single-layer and double-layer armor), etc.
10. At present, optical cables for communication can be divided into
(1) Indoor (field) optical cable, which is used for outdoor direct burial, pipeline, trough, tunnel, overhead and underwater laying.
(2) Soft optical cable, which is a movable optical cable with excellent bending performance.
(3) Indoor (office) optical cable, which is suitable for indoor laying.
(4) In-equipment optical cable, which is used for laying in equipment.
(5) Submarine optical cable, which is used for laying across the ocean.
(6) Special optical cable, which is used for special purposes in addition to the above categories.
3. Identification method of optical cable model
The model naming of communication optical cable is based on my country's communication industry standard YD/T 908-2000. Composition of optical cable model: The model consists of two parts: type and specification, with a space between type and specification.
1. Classification code
Note: Between the first and second parts: code for reinforcement (strengthening core)
Strengthening components refer to components inside or embedded in the sheath to enhance the tensile strength of the optical cable:
No symbol - metal reinforcement component; G - heavy metal reinforcement component F - non-metal reinforcement component; H - heavy non-metal reinforcement component
(For example: GYTA: metal reinforcement core; GYFTA: non-metal reinforcement core)
2. Codes for filling structural features in cable core and optical cable
The structural features of the optical cable should indicate the main type of cable core and the derived structure of the optical cable. When there are several structural features of the optical cable type that need to be indicated, a combined code can be used to indicate it.
3. Sheath code
Note: Between Part 3 and Part 4:
The code is represented by two groups of numbers. The first group represents the armor layer, which can be one or two digits; the second group represents the coating layer, which is one digit
4. Armor layer code
5. Coating layer code
6. Cable specifications and models
IV. Other characteristics of optical cables
1. Optical fiber defects:
Quartz optical fiber has high strength when there are no surface defects. Unfortunately, although a protective layer is applied immediately during the drawing process to avoid cracks, long lengths of quartz optical fiber inevitably have some random surface defects. The size of these defects determines the strength of the optical fiber. Under stress, these cracks will gradually expand. High humidity will accelerate this expansion. When the cracks expand to a certain extent, the optical fiber will break. In order to ensure that the initial cracks of the optical fiber used are lower than a certain value, the optical fiber must be tension screened during the production process of the optical fiber. According to statistical laws, the screened optical fiber has a certain guaranteed strength.
In order to enable the laying and use of optical fiber in various environments, the optical fiber must be combined with other protective elements to make an optical cable.
2. Other properties of optical cables
The requirements for the performance of optical cables are based on the transmission performance, environmental conditions and laying methods of their use.
(1) The transmission performance of optical cables mainly depends on the characteristics of the optical fiber selected for the optical cable.
(2) The mechanical properties of optical cables include stretching, flattening, impact, repeated bending, torsion, and shooting.
(3) The environmental performance of optical cables includes attenuation temperature characteristics, drip performance, sheath integrity, water permeability and flame retardancy.
The life of optical fiber depends on the stress on the optical fiber and the humidity in the environment. Generally speaking, optical fiber is afraid of moisture and force. In addition, the attenuation of quartz optical fiber will increase under a certain hydrogen pressure. Therefore, optical fiber is also afraid of hydrogen.
3. Design principles of optical cables
In view of the weaknesses of optical fibers, the design of optical cables should follow the following principles:
(1) Provide mechanical protection for optical fibers to protect them from stress in various environments;
(2) Optical cables must be protected from moisture and humidity;
(3) Hydrogen must be avoided in optical cables, especially hydrogen damage.
5. Two Commonly Used Optical Cables
The commonly used optical cables produced by various manufacturers are divided into two types: loose tube layer-twisted type and central bundle tube type. The cross-sectional structure diagrams of the two optical cables are as follows:
Layer-twisted optical cable
At present, our company mainly produces layer-twisted optical cables. In layer-twisted optical cables, the sleeve is spirally twisted on the reinforcing core. The smaller the twisting pitch, the greater the degree of freedom of the optical fiber. If the pitch is too small, the curvature radius of the optical fiber will be reduced, thereby increasing the bending stress. Therefore, the twisting pitch of the optical cable is also an important process parameter of the layer-twisted optical cable and must be optimized. Ideally, the position of the optical fiber in the layer-twisted optical cable should be in the center of the sleeve. When the optical cable is stretched or contracted, the optical fiber will move inward or outward.
A (S) sheath difference and standard
(1) A (S) sheath standard
A (S) sheath optical cable should apply a longitudinally overlapped aluminum (steel) plastic composite tape moisture barrier layer outside the cable core, and at the same time extrude a layer of black polyethylene sleeve to make the polyethylene sleeve and the composite tape and the tapes at the overlap of the two edges of the composite tape bonded to each other as a whole. If necessary, an adhesive can be applied at the overlap to improve the bonding strength. The overlap width of the composite tape should not be less than 6mm or not less than 20% of the cable core circumference when the cable core diameter is less than 9.5mm. The nominal value of the polyethylene sleeve thickness is 1.8mm, the minimum value should not be less than 1.5mm, and the average value on any cross section should not be less than 1.6mm.
The nominal thickness of the aluminum (steel) tape is 0.15mm, and the nominal thickness of the composite film is 0.05mm. A small number of composite tape joints are allowed in the manufacturing length of the optical cable, and the distance between the joints should not be less than 350m. The joints should be electrically conductive and the plastic composite layer should be restored. The strength of the composite tape with joints should not be less than 80% of the strength of the adjacent section without joints.
(2) A (S) sheath difference
The sheath of the optical cable provides further protection for the optical cable. It enables the optical cable to have better mechanical properties such as lateral pressure resistance, impact resistance, and bending resistance. The sheath varies according to the purpose of the optical cable. (A) Aluminum tape longitudinal sheath is mainly used for moisture and water resistance, and (S) corrugated steel tape is mainly used to improve lateral pressure and impact resistance. 5.1.2 Water blocking problem of optical cable Since optical fiber is afraid of moisture and water, the optical cable must have good waterproof performance. Waterproof is divided into transverse and longitudinal water blocking.
Water blocking problem of optical cable
Since optical fiber is afraid of moisture and water, the optical cable must have good waterproof performance. Waterproof is divided into transverse and longitudinal water blocking.
(1) Transverse water blocking
Due to the vapor pressure gradient inside and outside the optical cable, in a humid environment, moisture or water outside the optical cable will penetrate and migrate into the optical cable. Strictly speaking, the plastic sheath of the optical cable cannot prevent the intrusion of tides for a long time. Once moisture invades the optical fiber, it will cause rust of the metal accessories and then electrochemical hydrogen evolution, which will not only corrode the metal parts, but also increase the loss of the optical fiber and affect the stability of the long-term transmission performance of the optical fiber. In order to prevent the lateral water seepage of the optical fiber, it is usually completed by longitudinally wrapping aluminum tape (steel tape).
(2) Longitudinal water blocking
During the laying process of the optical cable, due to local damage to the protective layer of the optical cable or accidental water seepage at the connection of the optical cable, water will invade the optical cable and penetrate along the longitudinal direction, which will not only affect the performance of the optical cable, but also the accumulated water will enter the junction box and terminal equipment, destroying the operation of the entire communication line. The traditional method of longitudinal water blocking of the optical cable is to use optical cable grease to block the gaps in the optical cable structure to prevent water from flowing in the optical cable. In addition, filling fiber grease, wrapping water blocking tape or winding water blocking yarn, and applying hot melt adhesive at the overlap of the steel tape can also play a certain role in longitudinal water blocking.
VI. Others:
(1) The main tensile component of the optical cable is the reinforcing core. Steel wire is generally used as the central reinforcing core, and phosphating steel wire is commonly used. In order to protect against lightning strikes or electromagnetic induction, optical cables need to use non-metallic reinforcing cores (FRP) instead of steel wire. In this case, aramid yarn can be added to the outer layer to make up for the lack of FRP strength.
(2) The optical performance of the optical fiber in the optical cable is the most important indicator of the optical cable because it directly affects the transmission of optical signals. Among the optical performance indicators, the attenuation of the optical fiber is the most easily affected during the production process of the optical cable.
(3) After the optical cable is laid, it must work continuously all year round. In the high temperature in summer and the severe cold in winter, the optical performance of the optical cable must remain unchanged or within the allowable range. This requires the optical cable to have good temperature performance.