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Choosing Materials for Optical Fiber Cables

Choosing Materials for Optical Fiber Cables

Optical fiber cables (also called fiber optics) are crucial for the long-distance data transfer that underpins modern business, industry, and society as a whole. In both loose-tube and tight-buffered fiber optic cable designs, polymer compounds are used for tight buffers, inner tubes, outer jackets, and sub-jackets to cushion the glass fibers at the center of the cable. These polymer elements protect the fibers from stress that could cause microcracks and lead to attenuation problems.

There are many polymer compounds designed to meet specific requirements. These include both PVC compounds and low-smoke halogen free (LSHF) compounds.

How do you choose a material for optical fiber cable?

Polymer compounds used in optical fiber cable need to have good physical properties, such as flexibility, tensile strength, and elongation. Compounds should also have good low temperature properties, because the cable needs to retain strength and perform even when it is exposed to cold, hot, and cycling from low to high temperatures.

Cables should have low shrinkage, so that the cable doesn’t pull away from a connector after installation. Shrinkage is affected by the material, including the base polymer’s melt index (which is an indication of how easily the material flows) and other fillers and additives in the compound. Shrinkage is also affected by processing because during extrusion, the polymer orients in the machine direction. Processing variables can be adjusted, depending on the compound, to optimize shrinkage.

Thermal stress cracking is another concern that can be mitigated with optimal materials and processing conditions.  

Flame retardancy is crucial for cables. Different cable types must meet different specifications for flammability. Regulations also vary by country.

Do compounds meet flame tests?

Flame tests are performed on a cable as an entire system, and they type of flame test depends on where the cable will be used. In addition, the cable design has a significant effect. A compound solutions provider can consider the overall design, including the various materials used, to determine what types of flame retardant additives and materials should be used in a particular cable so that it will pass its flame test and any smoke requirements.

In the US, cables are rated for where they are used in a building, such as those used in a cable tray, in a riser (a vertical space that passes from one floor to another), or in a plenum (the plenum or air handling space). In the US, plenum cables have the most stringent flame retardancy tests, and low smoke (LS) PVC compounds are used here. In other countries that have less stringent flame and smoke requirements, LSHF compounds can be used in these applications.

In Europe, optical fiber data cables do not use PVC; all are LSHF.  These halogen-free compounds use alternative materials that do not contain any halogens (such as bromine or chlorine) in the polymer itself or in any of the flame retardant additives.  You can read more about how LSHF are designed to improve fire safety. (https://www.alphagary.com/blog/lshf-wire-cable-compounds-improve-safety-in-a-fire/3197/)

The Construction Products Regulation (CPR), which applies to cables sold into the European Economic Area, has specific testing requirements for cables, which are classified under categories A to F, depending on their performance in flammability tests

Each country can have its own regulations, and may require certain ratings (such as B2, C, or D) for cables in construction. A cable manufacturer needs to know specifically what country the cable will be used in, what application, and what rating they need in order to determine what materials should be used in the cable design.

Fiber optic cable material solutions

Cable designers can talk to AlphaGary experts to identify the best compound for their design. AlphaGary has various solutions to meet different requirements for flame retardancy while preserving other critical properties.