A preform production day at UNAM
In order to transmit the light with low attenuation in a glass fiber optic, impurities should be kept minimum as OH– ions preserved in the ppm levels. One of the method to get this glass fiber with high purity is well-known method called Modified Chemical Vapor Deposition (MCVD) which gives one to create glass soot particles and deposite them on the inner surface of a tube in a planned manner and then sinter by moving torch to get the pure glass layer. The production of such high quality fiber preforms is done by using the recipies written by ORTAÇ Group after the optimization of every step.
Some part of the preform production recipe written in MCVD by Ortaç Group
All items related with the production of the preform compose the recipe which is written just before each production by Ortaç Group Engineers. Not only precursors and their carriage gases, but also their flow rate and temperature are some of the examples of the items in recipe.
In this method we can control the every second of the production by the software of MCVD
Different from CVD, MCVD gives us a chance to use the precursors in liquid, solid and gas phases at the same time. In summary, all the precursors are delivered to the rotating substrate tube in the gas phase by the carrier gases. At the end of all the chemical reactions while the glass soots are deposited on the inner surface of the tube, various exhaust products of reactions are vented through the scrubber unit.
Scrubber unit of the MCVD system
As a result we get the clear glass core surrounded by glass cladding which are designed by Ortaç Group. This design includes a certain amount and proportion of dopants in the glass core and the glass clad, which guide light in the core and let it to keep its path along its traveling. The various dopants can be added in the controlled amounts to make a variety of glass compositions which can have refractive indexes either less than, equal to, or higher than SiO2.
As mentioned, to get the fiber preform without impurities all precursors are sent to the system by a special way. Liquid phase precursors are sent to the system by bubbler as shown in the schematic representation but solid phase precursors are loaded to the MCVD reactors in the glove box which has the very low level of H2O (<0.1 ppm). After loading the chemicals in the glove box, the reactors are immediately inserted to the system to prevent precursors’ reaction with air.
Schematic represantation of fiber preform production by MCVD in 6 steps
After the glass core and clad production in the first 4 step, the substrate tube is collapsed to get the preform rod of our carefully engineered architecture in step 5. We frequently use the postprocesses (stretching and jacketing) to set the diameter of core and clad to the desired ratio.
By this method, at the end of 2018, Ortaç Group demonstrated the First National Active Fiber Preform fabricated under the Project 113A055 by the support of The Scientific and Technological Research Council of Turkey (TUBİTAK).