When fiber optic cable is made, there are two protection requirements for optical fiber: one is that the fiber is less forced, and the other is that the fiber is waterproof.

The outermost layer of the fiber optic cable is a plastic shield, inside is a metal sheath, and then inside is the water-blocking layer of water expansion, the cable core has ointment and fiber glued together. Optical fiber has four waterproof passes, namely: plastic shield, metal sheath, water-blocking layer, ointment. So, the problem came, fiber optic why so afraid of water, home fish tank glass, window glass why not afraid of water but waterproof, are glass why so different?

It is generally believed that fiber optics are not afraid of water, because glass is extremely water-attached. But in fact, water is very harmful to fiber optic cables. If the fiber optic cable into the water, in the cold water ice expansion will hurt the fiber, so the fiber optic cable needs to be filled with ointment to prevent moisture from entering.

Experiments show that the long-term loss of water into the fiber optic cable will cause the fiber to decrease and increase, especially at a wavelength of 1.55pm.

The reason fiber is afraid of water is that the fiber is made up of glass (Si04) silicon-oxygen tidal structures connected to each other, as shown in Figure 1. In a Si-O-Si network, oxygen atoms exist in the form of bridge oxygen. However, in a watery environment, the glass surface adsorption of water gas, slowly hydrolyzed reaction, resulting in the original network of one Si one 0 one Si one silicon oxygen bond break, bridge oxygen into non-bridge oxygen Figure 2, resulting in glass cracks, and cracks continue to grow.

Whether fish tank glass, window glass or fiberglass are afraid of water, the difference is that fish tank glass, window glass is very thick, thickness of 3mm, 5mm, 10mm, even if there is O.05mm cracks do not affect the strength of the glass, the naked eye can’t see the change. And fiber optic glass is different, fiber glass diameter is only O.125mm, as thick as hair, if there is O.05mm crack, fiber diameter is left O.075mm, so fiber optics are very easy to break fiber, in addition to the emergence of OH root will also increase the absorption loss of optical fiber to light. That's why fish tank glass, window glass is not afraid of water, and fiberglass is afraid of water.

Even so, fiber optic cable broken, connector box seal is not good, bare fiber exposure will be due to water lead to shorter fiber life, natural fiber.