1. Introduction of optical fiber
The full name of the optical fiber is called the optical fiber. The English name is OPTIC FIBER, and it is also called OPTICAL FIBER. It is made of pure quartz (glass) with a special process and is drawn into a glass tube with a medium in the middle. It can be used in a very short time. convey a huge amount of information.
The following is a process drawing of using a preform (that is, a high-purity glass rod) with high-temperature wire drawing. The bright part in the middle is the melted glass.
Fiber knowledge
This is a preform drawn into an optical fiber after being melted at high temperature on a draw tower. The optical fiber drawn below the picture is still very thick. When the drawing speed reaches the normal standard, the drawn optical fiber will become a finished optical fiber with uniform thickness. During the fiber drawing process of a preform, a certain amount of substandard fibers will be generated in the front part and the rear part. If the process control is not good in the middle, waste fibers or low-grade fibers will also be generated. Some fiber optic manufacturers will sell these waste fibers or low-grade fibers to some fiber optic cable factories that do not pay attention to reputation at a very low price.
2. Characteristics of optical fibers
The transmission speed is fast, the distance is long, the content is large, and it is free from electromagnetic interference, not afraid of lightning strikes, difficult to eavesdrop on the outside, non-conductive, no trouble of grounding between devices, etc.
3. Types of optical fibers
According to the transmission mode of light in the fiber, it can be divided into: single-mode fiber and multi-mode fiber.
Multimode fiber: The diameter of the central optical transmission part is: 50μm, the outer diameter is 125μm (micron), which is the European standard, so the model is called 50/125 (A1a is referred to as A1 or OM2 conventional model/OM3 10G model). 62.5μm, the outer diameter is also 125μm, which is the American standard, so the model is called 62.5/125 (A1b or OM1).
Multimode fibers can transmit light in multiple modes. But its intermodal dispersion is large, which limits the frequency of transmitting digital signals, and it will be more serious with the increase of distance. Therefore, the distance of multimode fiber transmission is relatively short, generally only 2 kilometers.
MMF (multimode fiber) commonly used description:
OM1 fiber or multimode fiber (62.5⁄125), the gigabit transmission distance is only 275 meters
OM2⁄OM3 fiber (G.651 fiber or multimode fiber (50⁄125)) OM2 has a gigabit transmission distance of 550 meters
The central transmission part of the OM3 fiber is also 50 microns, which is a 10 Gigabit fiber. The subdivision models are:
The OM3-150 reaches 10 Gigabit at a distance of 150 meters.
The OM3-300 reaches 10 Gigabit at a distance of 300 meters.
The OM3-550 reaches 10 Gigabit at a distance of 550 meters.
Transmission band: Multimode generally uses a laser with a wavelength of 850nm (nanometer) or 1300nm to transmit signals.
Single-mode fiber: The central glass core is thinner (the core diameter is generally 9μm, and some countries are called 8.3μm or 10μm, and the outer diameter is 125μm), so the model is called 9/125.
Only one mode of light can be transmitted. Because of its small intermodal dispersion, the transmission distance is hundreds of kilometers, which is suitable for long-distance communication. Operators generally use single-mode fiber for long-distance transmission.
Additional description of single mode fiber:
G652B, also expressed as B1.1 as a common single-mode fiber
G652D, also used B1.3 (low water peak fiber) operator's backbone network projects use this fiber.
G652D is 10 yuan more expensive than G652B fiber per kilometer.
Transmission band: Single-mode generally uses a laser with a wavelength of 1310nm (nanometer) or 1550nm to transmit signals. The optical fiber is made of high-purity quartz glass material, and the attenuation reaches the minimum near the light wavelength of 1550nm (close to the theoretical limit of 0.2dB/Km)
Some fiber-to-the-home projects use G657 fiber (bending-resistant fiber) that is 70 yuan per kilometer more expensive than G652B. This fiber has a small bending radius and is suitable for places with small turning angles.
4. Coating fiber at one time
The fiber drawn from the drawing tower generally needs to be coated with a UV-curable acrylic resin coating with a diameter of 0.25 mm on the skin. This can protect the fiber.
5. Other optical fibers
Industrial, Medical and Low Speed Networks: 100/140μm, 200/230μm
Plastic: 98/1000μm for automotive controls.
Indoor fiber optic cable
Indoor optical cable: Indoor optical cable is mainly composed of tight-buffered optical fiber, spun fiber and PVC outer sheath. Single-mode or multi-mode optical fibers can be selected for production according to actual application needs. The color of the outer sheath of single-mode indoor cables is usually yellow, the color of the outer sheath of multi-mode indoor cables is usually orange, and the color of the outer sheath of some indoor cables is grey.
Tight-buffered optical fiber: After extruding a layer of plastic on the surface of the bare optical fiber, the optical fiber in the tight-buffered optical fiber is tightly bound by the sleeve and cannot be loosened in it. It is an integral structure with the plastic jacket. General users need the outer diameter of the optical fiber plus the sheath to be 0.9 mm, and a small amount of it needs to be 0.6 mm. The tight packaging material is generally PVC, but also LSZH (low smoke zero halogen) or nylon.
Aramid: The full name is "poly-p-phenylene terephthalamide", and the English is Aramid fiber (DuPont's trade name is Kevlar Kevlar). It is a new type of high-tech synthetic fiber with ultra-high strength, high resistance High temperature, acid and alkali resistance, light weight and other excellent properties, its strength is 5 to 6 times that of steel wire, and it will not decompose or melt at a temperature of 560 degrees. It has good insulation and anti-aging properties. The discovery of aramid is considered to be a very important historical process in the material industry. Today's bulletproof vests and military helmets are generally made of aramid. The purpose of aramid fiber in optical cable is tensile strength and flame retardant.
High-strength yarn: also called domestic aramid, polyester yarn. Due to the high price of aramid fiber, it needs to be imported completely. Now many manufacturers choose high-strength yarn as the strengthening member of indoor optical cable. The advantage is that the tensile strength is close to that of aramid, and the price is less than one tenth of that of aramid. The disadvantage is that it is not resistant to high temperature and flame retardant.
Indoor optical cable sheath material: When it comes to indoor optical cable, we will encounter many customers who have specified the sheath material in the future.
PVC sheath material: This kind of sheath is the most commonly used. The advantages are that the raw materials are easy to purchase, the cost is low, the appearance is beautiful, and it has a little flame retardancy. The disadvantage is that it is not resistant to ultraviolet rays and cannot be exposed to rain, so the optical cable made of this material cannot be directly exposed to the sun, nor can it be exposed to water for a long time, otherwise it is easy to age. Generally only used as indoor optical cable sheath.
LSZH (Low Smoke Zero Halogen) sheath material: According to statistics, in the event of fire, 90% of the causes of death are due to suffocation and coma caused by the strong and even toxic smoke produced during combustion, which makes people lose the chance to escape. Therefore, in some important indoor environments, it is required to use materials that can be flame retardant and will not produce a lot of smoke and toxic gases once the optical cable is on fire. This material is much more expensive than PVC, and its density is much higher than that of PVC. The outer skin looks a bit like rubber.
Single core jumper cable:
This kind of cable is generally used for optical fiber jumpers in jumper factories. It is not specified to be low-smoke halogen-free (LSZH). Generally, PV is used as the sheath.
If there is a need for low smoke and halogen free, the inner tight packing material is usually PVC, and the outer sheath is low smoke and halogen free, and rarely, the tight packing is also LSZH. General outer diameter 2.8-3.0MM or 1.8-2.0MM
Jumper cable:
The structure of this type of optical fiber cable is the same as that of the single core, but there are many optical fiber jumpers that need to be combined with two cores. The process requirements ensure that one of the core outer skins will not be torn when tearing, and the outer diameter of the two cores should not deviate too much.
The material is also PVC or LSZH.
Outer diameter: general outer diameter 2.8-3.0MMX2 or 1.8-2.0MMX2
Single-mode is generally yellow, and multi-mode is generally orange.
Multi-core indoor optical cable:
Because the aramid fiber is yellow, when we make the cross-sectional diagram, we make the outer sheath into a commonly used multi-mode orange color, and when we see that the outer sheath is light yellow in the physical picture above, we should judge that it is a single-mode indoor optical cable.
Indoor branch fiber optic cable:
When some indoor occasions require a large number of fibers with a number of cores, or when cabling needs to divide some fibers into different units, we will use the structure of the branch fiber optic cable.
