j-fiber Process technologies

For innovative fiber optics solutions in data communications and a wide range of specialty applications

At the Jena facility, j-fiber and j-plasma have established a unique center of excellence using versatile process technologies including:

  • MCVD processes (Modified Chemical Vapor Deposition)
  • POVD processes (Plasma Outside Vapor Deposition)
  • Molten glass for the production of high purity synthetic Fused Silica

The particular combination of the process technologies enables making fiber optic products and services, individually adjusted to the specific needs of our customers and the intended applications: from optical elements for laser applications to customized preform designs for large-core step-index fibers.

Molten glass

Synthetic Fused Silica is created from an ultrapure silicon compound by an chemical reaction called vapor deposition. This manufacturing technique guarantees highest purity and lowest optical absorption.

The process for producing Fused Silica developed by the former company “Jenaer Glaswerk” is characterized by the flame hydrolysis decomposition of the synthetic silicon tetrachloride – an ultrapure and colorless fluid. During hydrolytic decomposition in a hydrogen/oxygen flame, minute (50 nm) particles of silicon dioxide are created, which fuse into ultrapure Fused Silica cylinders at the extreme flame temperature (> 2700 K).

Since Fused Silica exhibits a large viscosity even at high temperatures, and to avoid contamination by fireproof materials, a pan-free technique is used to deposit the SiO2 particles onto the front face of a slowly rotating attachment. This attachment, which is made from natural quartz, is clamped in the carriages of a lathe and is moved away from the burner at a velocity that matches the fusing speed. This kind of fusing facility also includes a gas volume controller for the burner gases, a raw material feed unit (the liquid SiCl4 is vaporized in carefully controlled quantities), the PLC-driven plant control system, and the waste gas extractor. The waste gas produced by this process is extracted for separation and neutralization in a waste gas scrubbing plant.

The production process, from igniting the multi-nozzle Fused Silica burners developed in-house to achieving maximum ingot mass, lasts several days. The production in the melt furnaces runs in parallel and the process and its parameters are monitored continuously by the operating personnel.

POVD manufacturing process

The fluorine-doped step-index preforms are manufactured by using a plasma-based deposition process. Manufacturing a preform is a multi-stage production process in which the quality of the Fused Silica and the capabilities of the manufacturing technology itself are both crucial. We manufacture a wide variety of preforms for further processing in-house or for OEM customers.

Ultrapure Fused Silica rods are cladded with fluorine-doped silica layers to give the preform its required step-index profile. For this purpose, we use a high-frequency plasma burner to trigger the chemical reaction between silicon tetrachloride, oxygen, and a fluorine-rich gas. The plasma’s high temperature produces the deposition conditions that enable a very high concentration of fluorine in the cladding material.

MCVD preform manufacturing process

This process involves the production of Fused Silica from gaseous constituents. The generated silica structure has the high purity required for data transmission –, which is not achieved by any other kind of manufacturing process. During MCVD, a rotating Fused Silica tube is heated over a flame, and a gas mixture of silicon tetrachloride, germanium tetrachloride and various gases is fed through it. These components chemically react forming small glass particles. Layer by layer, the glass is gradually deposited and fused onto the inner surface of the tube.

Fiber drawing technology

The completed preform is prepared for the drawing process in our in-house drawing towers. This involves the preform being secured to the top of the tower and then heated in a furnace to over 2,000 °C. The drawing process starts with a first silica droplet. The material tapers more and more and is finally, after threading through all apertures of the tower, drawn to the size of a hair's breadth. During this process the fiber cools down to room temperature. Depending on the target fiber diameter, a preform can yield many kilometers of fiber. To protect the silica fiber, it is coated with a dual-layer acrylate coating during drawing. The coating protects the fiber against environmental influences making the fiber processable for cabling. The fiber has now achieved its characteristic diameter of 0.25 mm (or alternatively 0.5 mm). Once wound onto reels, the fiber is sent to quality control.