CuBALL coating properties
Comparison data

Oxford Electronics has been manufacturing metal-coated optical fibers for some time. The graph below shows a sample of aluminium-coated optical fiber, a sample of copper coated fiber, and two samples of the new CuBALL optical fiber for comparison. All fibers are 125 µm cladding diameter.

Strength of CuBall coated fiber at high temperature. Time dependence of bend strength of different types of metal-coated fibers (P = 50%). Temperature 500°C

Although the starting strength of all the above fibers is similar at about 8-10 GPa, the copper coated and aluminium coated fibers rapidly lose strength after heating to 515°C for a few hours. In contrast, the CuBALL samples are showing no signs of degradation after 35 hours.

A Weibull plot of strength data is shown for unheated samples, samples heated to 500°C for 24 hours and 34 hours respectively. Note that these tests were carried out in air. In an inert atmosphere there were no signs of degradation when the temperature was increased to 600°C.

Strength of fiber after heating Weibull plot of strength data of CuBALL fiber before and after heating to 500°C in air

High hermeticity

CuBALL fibers exhibit excellent hermeticity. In some environments where gases such as hydrogen or hydrogen sulphide are present, diffusion through the coating of polymer-coated fibers has been found to cause increases in attenuation and premature failure of the fiber. CuBALL fibers have much better resistance to diffusion through the coating compared to polymer coatings.

Low luminescence

Optical fibers are frequently required to transmit very low levels of fluorescent light. Most polymers exhibit some fluorescence and so should be avoided for sensitive measurements. These metal-coated fibers should be used for the most demanding applications.

High light isolation

When an optical fiber is bent in a small radius, light from outside the fiber can enter the fiber and can be a source of crosstalk in sensitive measurements. This phenomenon is frequently used by fusion splicers to induce light into the fiber for dynamic alignment of the cores but is usually undesirable in virtually all other cases. The opaque nature of the CuBALL cladding ensures that crosstalk or stray light input is at a minimum.

Solderable

CuBALL fibers are readily solderable using conventional techniques that lend itself to a number of useful applications. A soldered fiber can be used in vacuum applications where an epoxy joint could allow outgassing and contamination of the vacuum. Fibers can be soldered to connectors to make epoxy free connectors for vacuum use.

Multiple fibers can be soldered together to make fiber bundles that do not require epoxy. This can be of use in applications where fiber bundles are used to make low fluorescence measurements. Most conventional epoxies can fluoresce to a significant degree.