In the long-distance optical cable communication system, the optical fiber transmission characteristics should be stable for a long time, especially the long-distance trunk direct buried optical cable and the submarine optical cable system, which puts forward higher requirements for the long life of the optical cable. Generally, the service life of terrestrial optical cables is expected to have a safe use period of more than 20 years, while for submarine optical cables, the service life is required to be increased to more than 25 years, and the average time between failures is required to be 10 years. Therefore, how to extend the service life of the optical cable and how to use the optical cable correctly are important technical issues that people are concerned about. Let's talk about how to extend the service life of the optical cable from the perspective of the structure of the optical cable.

Three factors that affect the life of optical fibers in optical cables

Optical fiber is one of the most important constituent materials in optical cable. To improve the service life of optical cable, the most fundamental thing is to improve the service life of optical fiber. The main reasons for affecting the service life of the optical fiber are: ① the existence and expansion of micro-cracks on the surface of the optical fiber; ② the erosion of the surface of the optical fiber by water and water vapor molecules in the atmospheric environment; . Due to the above reasons, the mechanical strength of the optical fiber based on silica glass gradually decreases, the attenuation gradually increases, and finally the optical fiber is broken, terminating the service life of the optical cable.

Since there are always micro-cracks on the surface of the fiber, slow crack growth occurs in the atmospheric environment, the cracks continue to expand, and the mechanical strength of the fiber is gradually degraded. For example, a 125μm diameter silica fiber reduces the tensile strength of the fiber from 180kpsi (equivalent to 1530g tensile strength) to 60kpsi (equivalent to 510g tensile strength) after 3 years of slow change. The principle of the mechanical strength reduction caused by this slow change of the optical fiber is that when there are microcracks (or defects) on the surface of the optical fiber, it will not break immediately under the action of external stress, only when the applied stress reaches the critical value of the crack, fibers will break. When the quartz fiber is subjected to a constant stress less than the critical value, the surface crack will expand slowly, so that the depth of the crack reaches the critical value of fracture, which is the process of fiber mechanical strength degradation. The degradation of the mechanical strength of silica fibers is caused by a combination of the stress experienced and the erosion of water and water vapor molecules in the atmospheric environment.