Optical Fiber Made of Glass, Will it be Afraid of Water?

When the outdoor fiber cable is produced, there are two basic protection requirements for the optical fiber: first, the fiber is less stressed; second, the fiber cable must be waterproof
The outer jacket of the fiber optic cable is a plastic sheath, inside there is a metal sheath, inner has water blocking layer that swells with water. The optical fiber has four waterproof barriers, namely: plastic sheath, metal sheath, water blocking layer, jelly.

Then the question is coming, why is the fiber core so afraid of water, why the fish tank glass at home, and the window glass are waterproof, all are made of glass why has so much difference?
It is generally believed that optical fibers are not afraid of water because glass has excellent water adhesion properties. But in fact, water is very harmful to optical cables. If water enters the optical fiber cable, the frozen water will expand which damages the optical fiber, so the optical cable needs to be filled with jelly to resist moisture
Experiments have shown that the long-term submersion of moisture into the optical cable will increase the loss of optical fiber, especially at the wavelength of 1550nm,
The optical fiber is afraid of water reason is that the optical fiber is composed of glass (Si04) silica tetrahedron connected to each other, after the surface of the glass adsorbs moisture, the hydrolysis reaction occurs slowly, which causes the silicon-oxygen bond in the original network—Si—0—Si— to break, and the bridge oxygen becomes non-bridge oxygen ,resulting in glass cracks, and the cracks will continue to grow.
Whether it is fish tank glass, window glass or fiber optic glass are water-resistant, the difference is that the fish tank glass and window glass are very thick, with a thickness of 3mm, 5mm, l0mm, even if there is a crack of O.05mm does not affect the strength of the glass , The naked eye can’t see the change. The optical fiber glass is different. The glass diameter of the optical fiber is only O.125mm, as thick as a hairline. If there is an O.05mm crack, the fiber diameter will be O.075mm, so the fiber is very easy to break and increase the optical fiber absorption loss. This is why fish tank glass and window glass are not afraid of water, but fiber glass is.
Hence when the jacket damaged or the splicing closure without good sealing function, exposed bare fiber can shorten the fiber cable life time.