What You Need to Know About Fiber Optic Cables
Fiber optic cables are the cornerstone of modern communications, distributed in all corners of the world, linking the entire world into a network. It is precise because of the existence of this network that people in different locations can do many things together on the Internet, such as video chat, online courses, watching movies, games, and communication.
Fiber Optical cable is so important, now let’s get to know the optical cable. Here is a summarize the content of this article.
Fiber Optical cables are mainly composed of two components:
1. The fiber core, that is, the optical fiber, is the channel of optical transmission and the core part of the optical cable, which determines the optical performance of the optical cable.
2. The foreskin refers to the protective outer skin wrapped around the fiber core. The function of this part is mainly to protect the core from damage. Because the optical fiber is very fragile, during the installation process, the external environment may damage the optical fiber, making the optical fiber unable to work normally.
1. The composition of the Fiber optical cable
1.1. optical fiber
Optical fiber is the core part of fiber optic cable. The diameter of the fibre core can be different:
When the core diameter of the fiber is 9um, only one mode of light can be transmitted at the same time, which is called a single-mode fiber.
When the core diameter of the fiber is 50um, 62.5um, or even larger, it can transmit multiple modes of light at the same time, which is called multimode fiber.
1.1.1. Single-mode fiber
According to the definition of ITU, there are several types of single-mode fiber, such as G652, G653, G654, G655, G656, and G657, each of which has its own performance characteristics and is suitable for different occasions. Here is a brief introduction to the basic characteristics and application scenarios of different optic fibers:
Features: (1) The dispersion at the wavelength of 1310nm is zero. (2) The attenuation coefficient is the smallest near the wavelength of 1550nm, about .22dB/km; but it has the largest dispersion coefficient near 1550nm, which is 17ps/(nm·km);
Application scenario: the most widely used optical fiber.
Often called dispersion-shifted fiber (DSF=Dispersion Shifted Fiber), its zero-dispersion wavelength is shifted to 1550nm, where the loss is extremely low; Disadvantages: AT&T in the United States discovered the serious deficiency of DSF in the early days, and there are harmful four-wave mixing in the low-dispersion region near 1550nm. Fiber nonlinear effects such as frequency, etc., hinder the application of fiber amplifiers in the 1550nm window.
Application Scenario: Mainly used for submarine optical cable, long-distance communication.
Features: Ultra-low loss fiber
Application scenario: transoceanic seabed
The dispersion is not zero at the wavelength of 1550nm, but the dispersion is extremely low, close to 0; the dispersion value remains non-zero to suppress the influence of nonlinear effects such as four-wave mixing and cross-phase modulation;
Application scenario: mainly suitable for dense wavelength division multiplexing transmission system.
Features: Use wider frequency than G655, 1460nm to 1625nm
Application scenario: a broadband system of DWDM and CWDM.
Features: Compliant with G652D standard, and smaller bending radius
Application scenario: FTTH and other places where the space is small and the bending radius is high.
For more knowledge about single-mode fiber classification, you can also visit introduction to G651,G652,G653,G654,G655,G656,G657 Fiber
1.1.1. Multimode fiber
Multimode fiber, that is, G651 fiber defined by ITU. Initially, the International Electrotechnical Commission recommended four graded-index multimode fibers with different core/clad sizes, namely A1a, A1b, A1c, and A1d. Their core/cladding diameters (μm)/numerical apertures are 50/125/0.200, 62.5/125/0.275, 85/125/0.275 and 100/140/0.316, respectively. Generally speaking, a large core/package size leads to high production cost, poor bending resistance, an increase of the number of transmission modes and a reduction of bandwidth. In addition to the above shortcomings, the 100/140μm multimode fiber has a large cladding diameter, which does not match the test equipment and connecting devices, and is soon not used in data transmission, only for special occasions such as power transmission. 85/125μm multimode fiber is being phased out for similar reasons.
Therefore, the main multimode fibers on the market are 62.5/125 and 50/125;
The 62.5μm core diameter multimode fiber has a larger core diameter and higher numerical aperture than the 50μm core diameter multimode fiber, and can couple more optical power from the LED light source. Therefore, the 62.5/125μm multimode fiber was first adopted by the United States as a number of industry standards. Such as the indoor wiring system standard of AT&T, the local area network standard of the American Electronics Industry Association (EIA), the 100Mb/s token network standard of the American National Standards Institute (ANSI), and the computer optical fiber data communication standard of IBM. 50/125μm multimode fiber is mainly used in Japan and Germany as a data communication standard. However, due to the large number of optical fibers in North America and the leading role of optical fiber manufacturing and application technology in the United States, most countries, use 62.5/125 μm multimode optical fibers as local area network transmission media and indoor wiring. 62.5/125μm optical fiber once became the mainstream product in the data communication optical fiber market.
However, with the increasing demand for bandwidth, the local area has developed from hundreds of megabits of bandwidth to 1G and 10G. Only the 62.5/125um multimode fiber that supports hundreds of megabits of bandwidth is obviously unable to meet the requirements. Multimode fibers with a core diameter of 50um have begun to be applied on an increasingly large scale. 50/125μm fibers have smaller numerical apertures and core diameters, higher bandwidth than 62.5/125μm fibers, and can reduce production costs by 1/3.
Another reason for using a 50-µm core is that the advantages of multimode fibers with a 62.5-µm core were previously viewed as being irrelevant with advances in light source technology. In the early and mid-1980s, LED light sources had low output power, large divergence angles, and large connector losses. Using fibers with large core diameters and numerical apertures to inject as much optical power as possible must be considered. With the application of the VCSEL light source, optical power injection is no longer a problem, core diameter and numerical aperture are no longer as important as before, and the transmission rate of 10Gbit/s has become the main contradiction, which can provide a higher bandwidth 50μm core diameter multimode Optical fiber is very popular. OM1->OM2->OM3->OM4 is the road of continuous improvement of multimode fiber performance, with larger and larger transmission rates and longer transmission distances. For the differences between OM1, OM2, OM3, and OM4, please refer to the xxx link. At present, there is already OM5, but it has not been widely used. In the future, it is more likely to have OM6, OM7…
1.2. Protection Layer
Another important part of the fiber optical cable is the protective layer that contains reinforcement, jacket and other protected materials. The outer layers itself does not participate in the transmission of optical signals. Its function is to protect the fiber core from damage. It determines the mechanical properties of the optical cable, which are determined by the material and structure. In different use environments, different materials and structures are required.
1.2.1. Structure of Fiber optic cable
Center tube type:
The advantages of the central tube type optical cable are: simple optical cable structure; simple manufacturing process; small optical cable cross-section; Lightweight, suitable for overhead laying, and can also be used for pipeline or direct burial laying. The disadvantage of central tube optical cable is: The number of fiber cores should not be too many, such as 12 cores for split fibers, 36 cores for fiber bundles, and 216 cores for fiber ribbons. Loose In the sleeve extrusion process, the cooling of the loose sleeve is not enough, the loose sleeve in the finished optical cable will shrink back, and the optical fiber in the optical cable will shrink. The excess length is not easy to control, etc.
Layer stranded type:
The structural characteristics of the layered optical cable are: the number of optical fibers contained in the optical cable is large, and the excess optical fiber in the optical cable is easy to be Control; the mechanical and environmental performance of the optical cable is good, it is suitable for direct burial, and pipeline laying, and can also be used for overhead laying.
The disadvantages of the layered stranded optical cable structure are: the optical cable structure process equipment is more complicated, the production process is more complicated, Material consumption is high.
Grooved cable: This is rarely used.
The advantages are compact structure, small cable diameter, and fiber core density.
Large (thousands of cores to thousands of cores) do not need to remove water-blocking ointment during construction and connection, and the connection efficiency is high.
The disadvantage is: that the manufacturing equipment is complex and a dedicated skeleton production line is required. There are many process links, and the production technology is difficult.
1.2.2. Raw Material
Below is the main raw material for the protection layer of fiber optic cable.
1. Polymer materials
(1) loose tube material
Commonly used materials are PBT, PP, PC; PBT is mainly used on the market at present, it has excellent mechanical properties, thermal stability, dimensional stability, chemical resistance, as well as filling water-blocking ointment for optical fibers and coating for optical cables. Good compatibility with water blocking ointment
(2) Polyethylene sheath material
The polyethene sheath material is used as moisture-proof protection for the cable core, which is called the inner sheath. The inner sheath is further divided into polyethene Sheath Y Sheath Aluminum-Polyethylene Bonded Sheath A Sheath, Steel-Polyethylene Bonded Sheath S Sheath
Steel-polyethylene bonded jackets with parallel wires W jackets, etc.
(3) Halogen-free flame retardant polyolefin sheath material
Halogen-free flame retardant polyolefin sheath material is mainly used as the outer sheath of optical cables with low smoke halogen-free flame retardant requirements.
(4) Track-resistant black polyethene sheath material
all-dielectric self-supporting fiber optical cables (ADSS cables) installed on overhead power lines When the potential is greater than 12Kv, In order to prevent electrical tracking and electrical corrosion on the outer sheath of the optical cable due to discharge, The outer sheath of the optical cable must choose a polyethene sheath material that is resistant to electrical tracking.
(5) High-density polyethene insulating material
High-density polyethene insulating material is known for its excellent mechanical properties, chemical stability and good electrical properties. It can be used as a skeleton and a filling rope material in optical cables, respectively.
(6) Water blocking ointment
The optical fiber is extremely sensitive to the hydroxyl radicals produced by water and moisture; in order to prevent water and moisture from penetrating into the optical cable! It is necessary to inject the fiber with water Fillingcompound into the loose tube longitudinally and fill the other gaps in the longitudinal direction of the cable core with the cable resistance. The flooding compound is designed to prevent the longitudinal seepage of water to the loose tube and the cable core after the rupture of each sheath.
(7) Polyester belt
Polyester tape is used as a wrapping material in fiber optic cables. For example, in a layer stranded fiber optic cable, the cable core is centred on the metal central strength member or the loose tube is twisted around the central strength member. The gaps between the loose tubes are filled with water blocking ointment for the cable, and finally the polyester The tape wrap constitutes the finished cable core.
(8) Water blocking belt
There are two water blocking methods for optical cables: water-repellent water blocking and water-absorbing swelling water blocking.
The water-blocking tape is a tape-shaped material formed by adhering water-absorbing resin to two layers of polyester fiber non-woven fabric with an adhesive. When the water infiltrated into the optical cable is in contact with the water-absorbent resin in the water-blocking tape! The water-absorbent resin quickly absorbs and penetrates Water, its own volume rapidly expands hundreds or even thousands of times. The expansion volume fills the gaps of the optical cable, thereby Prevent the further flow of water in the longitudinal and radial directions of the optical cable to achieve the purpose of blocking water.
(9) Aramid yarn
Aramid yarn is placed between the inner and outer jackets of the fiber optic cable to give the cable a large longitudinal tensile strength.
(1) Phosphated steel wire: Phosphated steel wire is used instead of galvanized steel wire for the central metal reinforcement of the fiber optical cable. Because the cable uses water blocking ointment The acidic zinc element is an active metal that will replace hydrogen, and the diffusion and penetration of hydrogen will cause hydrogen loss in the fiber.
(2) Fiber Reinforced Plastic FRP, non-metallic reinforcement, The main features are lightweight, good mechanical properties and anti-electromagnetic interference. The central reinforcement in the ADSS optical cable on the high-voltage power transmission line should be a glass fiber reinforced plastic reinforcement to avoid the effect of lightning and electric fields.
2. Optical cable use environment
The choice of material and structure in actual use is determined by the specific applications, and the cost is also considered. In general, the environment can be divided into two parts:
- Indoor, the indoor feature is that there is no need for waterproofing, and the indoor temperature fluctuation is relatively small. But consider fire protection. The indoor environment is generally mild, and the requirements for the strength and durability of optical cables are not so high. Indoor optical cables generally use a tight buffer structure. The structure of fiber optic cable is relatively simple. The number of fiber cores is generally relatively small, generally less than 24 cores, and most of them use a central tube structure.
- Outdoor, outdoor features should consider waterproof, UV protection, and large temperature changes. The outdoor environment is generally harsh, and the mechanical performance required for optical cables is relatively high. Outdoor optical cables are generally trunk lines, and the number of optical fiber cores is relatively large. Generally, it will be larger than 24 cores, and most of them use a layer stranded structure.
Outdoor applications are generally divided into:
- Undersea: Waterproof, high pressure resistant, anti-shark bite. Submarine cables are generally strong in construction, with multiple layers of armour to withstand high water pressure and resist shark bites.
- Direct burial: pressure-resistant, waterproof, generally using double-sheathed armoured structure. Such as GYXTW53
- Duct: waterproof, anti-rodent, GYTS, GYTA, etc. can be used for duct laying.
- Overhead: considering environmental factors such as wind, icing, span, etc., the weight is generally relatively light. OPGW, and ADSS are common overhead cables. Generally, Kevlar and FRP center reinforcements are used.
3. Splicing of fiber optic cable
There are two ways to splice the optical cable, one is fusion splicing,
The fiber optic cable is packed as drum, each drum has a limited length, usually 2~3km. So fusion splicing is needed when deploy as in real applications the cable needed is much much longer than a drum length. The fiber optic splice closure is needed to protect the splice point where fusion splice is done.
The other is through couplers. The fiber cable is preconnectorized and splices the two optical cables through the adapter to match the butt connector. The fiber optic cable which is preconnectorized is called fiber patch cable or patch cord. This is for a quick connection between two points not far away from each other. Usually for indoor applications or used in cabinets or distribution boxes.
As a manufacturer of fiber optic cable, anfkom provides different kinds of fiber optic cable and fiber patch cable. Any inquiry is welcome, please send an email to firstname.lastname@example.org.