Fused silica rods for optical fiber

High purity fused silica rods generally serve one of three purposes in optical fiber production:

  • As a material which later forms the light-conducting core of the fiber. These rods should be made of a material which has a low absorption in the desired wavelength region. This rod must then be provided with a cladding. This fiber either is a plastic clad pure silica core fiber (PCS) or the rod is given a quartz glass cladding with a lower refractive index (multi-mode fiber).
  • For forming a preform for photonic crystal fibers (PCF) (stacking of different glass pieces, or drilling holes into the rods).
  • For locally adjusting the refractive index or the generation of mechanical stress in the fibers. One possibility for producing polarization-maintaining fibers is to use two stress inducing Boron doped rods..
  • As an aid for the production of optical fibers.
High purity fused silica rods

These rods are predominantly used as a material for preforming various fiber types. The requirements differ depending on the fiber type. Typically, it is either a low absorption, a specific refractive index value or certain geometrical specifications.

Rods with a reduced refractive index

These fluorine doped fused silica rods allow you to produce individual preforms or to test new designs by rather simple mechanical or hot processing. The typical size is round with an outer diameter of 1 mm to 50 mm, but custom diameters are available upon request. For more details, please contact our experts.

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 preforms 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.

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