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High Purity Substrate Tubes

Heraeus substrate tubes are the premier choice for production of core rods for single mode, multimode, and specialty optical fibers. Our tubes are utilized in MCVD (Modified Chemical Vapor Deposition) and similar deposition processes used to manufacture core rods. The core material of the final fiber results from the deposition of multiple layers of pure and Germanium doped fused silica on the inner surface of the substrate tube. Oxygen-hydrogen burners (MCVD), electrical furnaces (FCVD) or plasma torches (PCVD) can be used as energy sources for these chemical deposition processes using Heraeus’ substrate tubes. Once the core material is deposited, the tube is gradually collapsed into a solid core rod under high heat and vacuum.

The most notable features of Heraeus substrate tubes are their unmatched purity and low hydroxyl (OH) content. These characteristics combined with a wide range of available geometries enable our customers to design core rods in such a way that the substrate tube material can be in close proximity to the core region of the final fiber. In the case of low water peak fibers, it is possible to achieve b/a values below 2 for single mode fibers, considered now state-of-the-art for inside CVD performs. This low b/a allows our customers to produce larger core rods, increasing the efficiency and productivity of their MCVD lathes while maximizing fiber quality and yield.

The right material to meet the desired application:
For single mode and multimode fibers, Heraeus has developed two material grades, F300 and F500. Both types of material are characterized by a very low OH content. F300 grade with OH levels below 1 ppm is the long time standard in the fiber optics industry. Heraeus’ advanced F500 material grade is an optimized water free material, with OH levels below 100 ppb, for low water peak applications.



OH [ppm] specified
OH [ppm] typical
≤ 1
≤ 0.1
CI [ppm] ≤ 2,500 ≤ 2,500
Trace impurities Below detection limit of ICP-MS
Typical values, if not stated otherwise


Heraeus offers a wide range of geometries . Our substrate tubes are drawn without using forming dies from large machined cylinders of the highest purity synthetic fused silica. This contact free proprietary process results in high geometric precision and tube surfaces which are free of contamination. The outside diameter and wall thickness can be precisely adjusted to the customer's requirements.

Typical Geometrical Performance

Outer diameter +/- 0.1 ... 0.2 mm
Wall thickness +/- 0.08 ... 0.2 mm
Ovality 0.03 ... 0.07 mm
Siding 0.07 ... 0.12 mm
CSA deviation 1 ... 2 %
Bow 0.2 ... 0.4 mm/m