The 125μm fiber drawn from the preform is thermally deformed, but there are still micro-cracks on the surface of the bare fiber. Once it is exposed to the atmosphere, the OH- in the atmosphere will cause the micro-cracks to expand. And prolonged exposure will cause the fiber to break.
In order to enhance the strength of the optical fiber, a thin layer of resin should be coated on the optical fiber in time during the drawing process and dried in time to avoid this and mutual adhesion.
After the drawing is completed, the finished optical fiber also needs to be tested. There are mainly tests for tensile strength, refractive index, fiber structure, attenuation, information carrying capacity (bandwidth), dispersion, operating temperature and humidity range, etc.
This is how optical fibers are made. It is this little glass filament that has completely changed our life today.