J-Fiber Jena

Guided tour: The secret of transforming gas into glass - A tour through purity and expertise

“Welcome to our course through j-fiber’s manufacturing facility. Here j-fibers are being produced. We will show you, how gas is being transformed into preforms and optical fibers of highest purity and uniformity. These are a fiber’s key criteria as they later ensure the fast and uninterrupted long distance transmission of information.

Before we enter our facility, our employees change into cleanroom suits to maintain a clean production environment. We will then meet our fiber making experts: Craftsman in the tradition of glass making working together with engineers and physicists. Together they combine their crafts, skills and know-how to make world-class optical fibers."

Process Step 1: Manufacturing the preforms – For glass of purest quality


The first step in manufacturing an optical fiber is the production of the preform. The deposition from gaseous ingredients results in a glass structure with such a high transmission purity that no other glass can even approximate.


We first make a primary preform. A rotating quartz glass tube that is sealed airtight is being heated over a flame. Gas flows through the tube. Now, a chemical reaction occurs. The reaction products melt onto the inner wall of the tube. The deposited glass forms the tube narrower and narrower. Next step is to close the remaining opening in the tube, the so-called collapsing. Now we have finished what will be the later core part of the fiber.


What we then do is called “jacketing”: The primary preform, the future core glass, free of impurities, is inserted into a solid jacket of pure quartz glass, SiO2. Core and jacket melt into the secondary, the final preform.”

Process Step 2: Drawing the fiber - The phenomenon of uniformity


“After jacketing the secondary preform is ready for the drawing of the fiber in the plant's drawing towers. The preform is fastened at the top, and heated in a furnace to more than 2,000 degrees Celsius. In the beginning a thick drop of glass separates and slowly drops down, drawing a glass fiber behind it.
The fiber is then coated with a protective layer of acrylate. The material allows the customer to easy handle and further process the fiber and to integrate it into a wide variety of cables. The coating consists of two layers. They protect the optical fiber, which has now reached its characteristic thickness of 0.25 millimeters, or optionally even 0.5 millimeters. The material cools on its way down and is wound onto spools.


It is always fascinating: Due to the uniform heating of the preform the glass runs off in such a manner that the profile of the preform is preserved in the fibers – although shrunken to a fraction of a millimeter. It is hard to believe, but a few millimeters of the solid glass cylinder can be stretched to more than 300,000 times its length. Thus one preform is enough to make several hundred kilometers of fiber.”

Process Step 3: Testing– High quality fibers ready for the customer


Before the fiber can leave our plant it has to pass several measuring procedures, material proof tests and quality controls.

“We have now reached the end of our tour. If you have further questions about how fibers are made by j-fiber please feel free to contact j-fiber under info@j-fiber.com”



j-fiber GmbH
Im Semmicht 1
D-07751 Jena, Germany

Tel: +49-3641-352 100
Fax: +49-3641-352 101