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How to ensure the service life of the optical cable

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-03-11

In the long haul optical communication system, optical fiber transmission characteristics should be long-term and stable, especially the trunk optical cable and cable system, put forward higher request to the cable life. General on terrestrial cable service life, hope to have more than 20 years of safe use period, the submarine cable, requires its service life up to 25 years, the time between failures for 10 years on average. Therefore, how to extend the cable service life, how to properly use the optical cable, are an important problem that people cares, below from the talk about cable structure how to prolong the service life of the cable.

Three major factors influence the life of optical fiber cable

Optical fiber is one of the most important optical component materials, to improve the service life of the optical cable, the most fundamental is to improve the service life of the optical fiber. The reason that influences the life of fiber are: ① fiber surface micro cracks in existence and the expansion of the atmospheric environment; erosion of water and water vapor molecules on the surface of the fiber; unreasonable laying cable residual stress the long-term effect. Because of the above reasons, so that the optical fiber mechanical strength to the quartz glass based gradually reduced, attenuation increases slowly, finally make the fiber fracture, the service life of the cable termination.

Due to the fiber surface micro cracks will always exist, slow crack growth in the atmospheric environment, the crack expanding, the mechanical strength of fiber degeneration gradually. For example, a 125 μ m diameter quartz fiber, after a slow change 3 years later, the tensile strength of fiber from 180kpsi (equivalent to 1530g tensile strength), down to 60kpsi (equivalent to 510g tensile strength). Optical fiber the slow changes caused by mechanical strength reduction principle is: when the fiber surface micro crack (or defects), under the external stress, and not immediately break, only the stress applied to the crack critical value, fibre will fracture. Quartz fiber subjected to a less than the critical value of the constant stress, surface cracks will occur slowly expanded, critical value of the crack depth is broken, this is the fiber mechanical strength degradation process. Degradation of quartz optical fiber mechanical strength is subjected to stress and atmospheric environment in the water and water vapor etching combined effect

Method for prolonging the service life of the optical fiber

When the fiber in a vacuum environment, in the absence of water molecules, so will not occur stress corrosion, fatigue parameter n to the maximum value, the fiber also has the highest intensity, the inert strength and strength is the fiber, called Si.
The service life of the TS fiber is in use environment and it bears should has the following relationship between stress and inert strength of Si fiber:
Lgts=nlg σ LgB (N2) lgS

Back in two are constants, so when the stress is constant should be subjected to fatigue life of TS, n parameters of fiber and fiber is related to the value of. The n value is large, TS fiber has longer life. Therefore, there are two ways to improve the service life of the optical fiber:

First, when the fatigue parameter n is certain, life of TS fiber and subjected to stress, therefore, reduce the stress fiber subjected to is a method of improving the lifetime of optical fiber. When people make fiber, the formation of a compressive stress to fight the bear to Zhang Yingli on the fiber surface, make Zhang Yingli reduced to as small as possible extent, hence the compression stress to manufacture fiber cladding technology.

If the set stress fiber is subjected to the σ a, service life is T1, when the fiber has compressive stress σ R cladding, fiber for the life of t
T2= t1[(σ a- σ R, σ a]-n

Among them, (σ a- σ R) for the net stress fiber really bear to. This shows that: with the stress fiber cladding fiber force than the general life much longer. In recent years some people use GeO2 doped silica fiber surface compression layer, there are clad with TiO2 doped silica fiber to do tensile strength of fiber itself is increased from 50kpsi to 130kpsi (equivalent tensile strength was increased from 430g to 1100g), the static fatigue parameters of fiber increased from n=20 to 25 to n=13

Second, improve the N static fatigue parameters of fiber to improve the service life of the optical fiber. Therefore, people in the manufacture of optical fiber, quartz fiber itself and managed to cut themselves off from the atmospheric environment, which is not affected by the atmospheric environment, the n value change from environmental material parameters for the parameters of optical fiber material itself as far as possible, can make the n value becomes large, resulting in the seal coating technology of fiber surface "".

In the recent ten years, the use of "seal coating technology" to manufacture fiber made great progress. The coating material by the metal to metal oxide, carbide, nitride, carbide inorganic inorganic, nitrogen oxides and CVD deposition of amorphous carbon. The coating layer structure consists of a metal coating layer single to sealing composite coating layer structure of coating layer and the organic coating layer combination, make the fiber has more practical application value, fiber optical properties, mechanical properties and fatigue properties are improved. For example:
Metal coated fiber: aluminum coated fiber can bear 1Gpa (150kpsi) stress, submerged in water, used in the temperature of 350 DEG C, life in 10 years.
Fiber metal oxide and other inorganic coating: C4H10 and SiH4 overlayers seal Si0.21O0.22C0.77 deposited on the fiber surface, and coated with organic layer, fiber n value can reach 256.
The boron nitride as fiber sealing coating layer: 200kpsi can withstand the tension, n value can be increased to more than 100. And as the optical fiber sealing coating TIC with 400 ~ 500kpsi strength, resistance to 100 ℃ water.

The amorphous carbon hermetically coated fiber: in inorganic coating material, amorphous carbon coating layer not only has little damage on the optical properties and mechanical strength of fiber, and showed good water resistant and anti hydrogen performance. This technology has been industrialized production. Typical tensile strength of this fiber has reached 500 ~ 600kpsi, dynamic n value of 350 ~ 1000. At room temperature after 25 years, carbon hermetically coated optical fiber hydrogen diffused in the only common fiber in fiber optic cables, 1/10000; hydrogen pressure of such fibers can be allowed is 100 times higher than the average fiber. The optical fiber can be appropriate to reduce the cabling conditions or use in high temperature conditions.

The use of fiber surface growth "compressive stress of clad" and "seal coating technology", fiber life available type launch:
T2/t1=19.36 * 10IR σ A
In the formula, a is the applied stress or stress. The relationship between a and t2/t1 calculated sigma. The service life of up to 40 years is expected to be used in optical fiber, cable and military communication.
Some studies also suggest that, manufacturing fiber Ning available germanium (GeO2) and fluoride (F) as dopant, without phosphorus (P2O5) as dopant, because phosphorus "hydrophilic (H2O)" is good, the fiber is susceptible to moisture, cause the core of the P-OH bond absorption attenuation increases, so that the fiber slow variation. So long use life of fiber end with phosphorus doped materials.
Humidity and water in the manufacture of optical technology, reducing the stress of residual

The first is the design of cable core, must use the loose structure, prevent leave stress remains, excess fiber strand cable to choose reasonable length, also can reduce the Zhang Yingli effect; filling oil gel in the cable core, in order to moisture-proof, waterproof, anti hydrogen containing compound (liquids) erosion; belt also to moisture using coated strip, aluminum, increase anti pressure, cable tension resistant ability; some factories in the cable core every aquitard a meter and a hot melt adhesive, preventing the penetration of cable core longitudinal water; strength element with a small linear expansion coefficient of the material as the core, is also the purpose of the protection of optical fiber, remove the external tension. The last point to point out, each kind of raw material is made of fiber optic cable, itself must have more than 30 years of life, there must be a high stability of the physical and chemical properties. Only the strict control of the manufacturing process quality, can prolong the service life of the cable.

Installation and construction process there is an important factor of course to extend the service life of the cable is the cable, the contents are rich and complex, should be separately as a special paper

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