Fused silica rods are used as a utility in optical fiber production. The first application can be during the deposition, the second during fiber draw.
- Handles for fused silica production by VAD:
In the VAD process, the front face of a fused silica rod serves as the deposition target for the soot. For this application the rod needs to have a low content of mobile metallic impurities (especially copper, Lithium, Sodium and Potassium, should be low). Depending on the exact setup of the process, bow and bubble content can be important as well.
- Handles for fiber draw
The prefroms used for drawing optical fibers are in most cases very expensive. To reduce the material loss in startup and end phases of the drawing process typically extension rods (so called handles) are used. Most common is the usage at the top of the preform to use it to mount the preform in the fiber-drawing tower to draw the whole preform to the end. Additionally the handle avoids any mechanical damage to the optical fiber preform by the holding unit of the draw tower.
A further application is the lower extension rod. This is typically shorter and smaller. When the preform is heated to melting, a first glass drop drips down, before the stable drawing of the fiber starts. Using a material with similar viscosity as a drop off piece saves original preform material, improving overall yield.