Early developments in optical fiber

Kao Charles
©Nortel/Emilio Segre Visual Archives, Hecht Collection

Charles Kao’s idea that high purity fused silica would allow transmission of data through a fiber was proven in 1970. By 1973, researchers at Bell Labs developed the MCVD process to make preforms using Heraeus fused quartz tubes. Layers of high purity fused silica were deposited on the inside of the tubes before they were finally collapsed to obtain the preform. The initial preforms were very small with an outer diameter of between 20- and 30-mm. Little more than a few hundred meters of fiber were produced in a single batch.

To improve batch size the MCVD process was used to produce the more highly-doped material needed for the core. To reach the correct ratio of doped core and undoped cladding, a un-doped jacket tube was collapsed onto the core rod. This sleeving process was called “rod in tube process” and was the basis for the future RIC process . Heraeus high purity tubes were used for both, the substrate tubes for the MCVD process and as the jacket tube. In the early 1990's, Heraeus introduced synthetic fused silica tubes to the market. These tubes have developed into the industry standard for fiber production because of their excellent geometric properties , surface quality and chemical purity.

Since the beginning of the industry and especially after the industry crisis in 2002, preform size has continually increased to lower costs. Heraeus introduced the RIC process, achieving the world largest preforms. From a single preform with an outer diameter of 200 mm and a length of 3 meters over 7000 km of single mode fiber can be drawn. This evolution in size has contributed to lower production costs and therefore contributed significantly to the success of fiber optic networks.

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