Analysis Of Fiber Optic Cable Aging Cases

The aging problem of fiber optic cable is hidden, but it poses a great threat to the operation quality and safety of telecommunication transmission network, which may cause significant losses to enterprises and requires our great attention.

Reasons For The Aging Of Fiber Optic Cable

The reasons for the aging of fiber optic cable, especially the serious deterioration of transmission performance that has not reached the expected life span and the general increase of loss throughout are various. There are mainly the following four reasons.

1. Hydrogen Loss

Hydrogen loss of optical fiber, in essence, is the process of hydrogen diffusion into the fiberglass, while reacting with defects in the glass, causing an increase in fiber attenuation at some characteristic wavelengths.

This process includes both physical and chemical processes.

The physical process mainly refers to the diffusion of hydrogen into the fiberglass. In this process, the hydrogen molecules do not react with the defects in the glass. Therefore, the hydrogen loss is only related to the absorption spectral properties of the hydrogen molecules that penetrate the fiber core.

The size of this hydrogen loss is only related to the concentration of hydrogen molecules in the fiber. At higher temperatures, less hydrogen is dissolved in the fiberglass, resulting in smaller hydrogen losses. The process is also reversible, when the external hydrogen atmosphere does not exist, the hydrogen in the fiber can leach out again and the hydrogen loss is eliminated.

2. Deterioration of Temperature Characteristics

The deterioration of fiber optic cable temperature characteristics may be caused by the following deep-seated causes.

1) The residual length of fiber optic cable at room temperature is large, and the residual length further increases at low temperature, resulting in larger macro bending loss.  

2) The residual length of fiber optic cable at room temperature is small, when the cable is at high temperature, the fiber is negative residual length, and the fiber sinks into the PBT tube wall, resulting in micro-bending loss of fiber.

3) As the sheath and PBT tube shrink at low temperature, “eat” the balance of the fiber in the splice box, so that the fiber in the splice box has a small bend, resulting in increased fiber loss or even breakage.

4) Poor integrity of fiber optic cable, forming a “piston effect”. That is, the degree of coupling of the components in the cable is not high, through several temperature cycles, the cable structure is loose, and the components of the cable like a piston with the temperature change and obvious contraction and expansion, causing fiber loss.

5) fiber optic grease and optical cable grease quality is not good. Such as fiber optic grease low-temperature cone into the degree of less than 200dmm, fiber paste hardened, its force can be added to the fiber to produce micro-bending loss. Another example is the fiber optic cable ointment high-temperature drip and oil separation. Which are caused by the fiber optic cable air gap, resulting in moisture infiltration into the fiber optic cable, the ointment water content will also make the fiber optic cable water vapor increase. This water vapor at low temperatures into tiny ice particles, resulting in fiber bending under stress, thus increasing the fiber optic cable’s low-temperature loss.

3. External Stress

Fiber optic cable in the cable, laying, and use process may be subject to stretching, bending, twisting and vibration stresses. These stresses act on the fiber and will lead to increased loss and reduced fiber strength.

4. Moisture

Optical fibers in fiber optic cables are susceptible to OH- ions generated by water and moisture. Water and moisture can cause microcracks on the fiber to expand, significantly reducing fiber strength.

When the fiber is exposed to moisture for a long time, its loss will increase and the fiber will become brittle.

This situation is generally characterized by an increase in fiber loss and an increase in natural fiber fracture.

In Comprehensive Analysis Of The Above Problems, The Author Proposes The Following Countermeasures.

1. Strict control of the project materials.

In the purchase of fiber optic cable, must be the structure of the cable form, the choice of raw materials, the production process, and technical indicators for a deep understanding, and comprehensive consideration. Not simply a few cores to compare the price of how much to measure. In particular, pay attention to the fiber optic cable and fiber paste manufacturers and quality, and do not choose too cheap but not strictly tested products.   

2. Strengthen contract management.

Choose poor quality raw materials or improper process production of fiber optic cable, often in the initial product testing, it is difficult to detect, because aging takes some time. Therefore, in the procurement contract to clarify the responsibility and compensation matters if an optical cable does not reach the expected life, require optical cable manufacturers to provide the corresponding optical cable selected optical fiber, fiber paste, loose tube, reinforced core, composite aluminum tape, sheath material, and other major raw materials manufacturers and specifications. Because of its long traceability period, must do a good job of the contract and the corresponding annex preservation and management.

3. Strengthen the analysis of the optical power changes of the bearing system on the fiber optic cable to find the problem in time. The aging of fiber optic cable is a gradual process, early detection can be early treatment or early prevention. Therefore, we should fully use the advantage of equipment always online, using network management means to collect optical performance parameters, and machine and line comprehensive analysis at the same time to do an excellent job of regular testing and analysis of the line.

4. The aging of optical fiber cable has appeared to downgrade the use or mixed with normal optical fiber cable. Cable aging caused by loss increase is directly related to the length, through the aging cable intervention length control, can make the starting loss change in the equipment tolerance value, and extend the cable in the network time. Such as the provincial trunk aging cable down to a short break for local networks, and such as a long-distance in a regeneration section, a section of normal fiber optic cable, and another section using an aging cable.

5. Good construction quality.

Engineering quality of aging cable also has a particular impact on the need to do a good job of engineering quality management. Especially the buried fiber optic cable insulation pass rate in the construction of strict requirements to prevent joints and fiber optic cable into the water.

6. Fiber optic cable construction should be carried out in batches evenly, preferably not concentrated in a few years to reduce the risk of aging.

7. Strengthen the investigation and analysis of fiber optic cable aging problems.

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