Frequently Asked Questions

FST tubes have a low OH content (<20 ppm), are available as uniformly doped tubes as well as customer-specific variations, and allow easy finishing and processing in preforms or capillaries. They have a thermal expansion coefficient of 2.5×107 K1, a density of 2.180 g/cm3, and an inner tube Ø (I.D.) of 20 – 40 mm.

FST tubes are used for a multitude of applications, including as substrate or jacketing tubes for special fiber designs, as substrate materials in CVD processes, for overcladding processes in preform production, and as Fluorine-doped capillary for special fiber designs.

FST fused silica tubes are ultrapure tubes made of fused silica that are doped with fluorine to meet the particular requirements of special fiber manufacturers.

FST tubes contain the highest fluorine concentrations of 4wt. %, resulting in a negative refraction index delta of (17 ±3) × 10 -3.

FST tubes are offered with numerical apertures (NA) of up to 0.22 (compared to pure fused silica).

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