Why is the glass fiber afraid of water?

- Dec 12, 2017 -

When optical cable is cable, there are two protective requirements for optical fiber. Second, the fiber should be waterproof.

The outer layer of the cable is the plastic sheath, which is a metal sheath, which is the water-resistant layer that meets the water, and the wick has the oil paste and the fibers sticking together. The optical fiber has four waterproof passes, namely: plastic sheath, metal sheath, water resistance and ointment. So the question comes, why is fiber optic why so afraid of water, the aquarium glass of the home, window glass why not afraid of water is waterproof, is glass why so different?

It is generally believed that the fiber is not afraid of water, because glass is very good in water. But the actual water is very harmful to the cable. If the cable is in the water, freezing in the cold water will report damage to the fiber, so the inside of the cable needs to be filled with oil to prevent water from entering.

The reason that fiber is afraid of water is that the fiber is made of glass (Si04) silicon oxygen tetrahedron, as shown in figure 1. In a Si - O - Si network, oxygen atoms exist in the form of bridge oxygen. But in water environment, the glass surface moisture adsorption, hydrolysis reaction slowly, then lead to the original network a Si a 0 a Si si-o bond rupture, in a bridge into the bridge oxygen as shown in figure 2, the result of glass cracks, and the crack growth.


Whether it is fish tank glass, window glass or fiberglass are afraid of water, the difference is the fish tank glass, window glass are thick, the thickness of 3mm, 5mm, l0mm, even with 0.05mm crack does not affect the strength of the glass, The naked eye can not see the change. The optical glass is different, the optical glass diameter of only 0.125mm, as thick as hair, if there are 0.05mm cracks, leaving a diameter of 0.075mm optical fiber, so the fiber is very easy to broken fiber, the emergence of OH root also will Increase the fiber optical absorption loss. This is why fish tank glass, window glass are not afraid of water, while fiber glass is afraid of water.

In both cases, the cable is broken, the joint box is not well sealed, and naked fiber exposure will lead to shortened fiber life and natural fiber breakage due to water exposure.