By: Johnny Hill

Environmental factors are just part of the practical hurdles not fully addressed by OSP standards.  The number one cause of fiber optic network downtime is equipment damage resulting from human error, either through rough handling or improper cable routing.  Even the best-designed fiber solutions can be easily compromised by routing and handling fiber circuits incorrectly.

While most technicians are both highly trained and diligent, interconnect cable must be able to withstand the real-world conditions presented by technicians who are rushed, inadequately trained or overly rough in their cabinet work.  The key to preventing damage to fiber cores due to crushing, impact or overly tight bend radius is in the cable construction itself.

In riser-rated jumper cables, the typical construction over the core and 125μm cladding involves a secondary 250μm coating of acrylate, followed by a 900μm PVC buffer, Kevlar strength members, and finally, an outer jacket of 1.6, 2.0 or 3.0mm outside diameter PVC.  The “loose tubing” inherent in such a design, combined with the inferior crush resistance of PVC, leaves such cable vulnerable to fiber breaks due to twisting or hard impact.

Again, this form of inside-rated cable, with its 250 micron diameter and 60 micron thickness, is insufficient for most OSP enclosure applications.  To reduce risk of damage caused by handling or blunt force, ruggedized cabling that meets U.S. Department of Defense (DoD) military performance standards is a far better choice.

The DoD’s Military Performance (MIL-PRF) 85045 specifications strictly defines the characteristics that allow fiber optic cable to operate properly under a huge range of environmental and deployment conditions.  The specification covers low temperature flexibility, crushing, barometric pressure, tensile loading, flammability, fungus resistance, fluid immersion, attenuation rate and many other factors.

To meet this demanding spec, an appropriate solution is to add a 500μm hard acrylate layer to the inner soft acrylate coating, followed by a 900μm, tight-buffered hard elastomeric material.  Together, these layers will provide improved crush and impact resistance.  An outer jacket of polyurethane significantly expands the operational temperature, while also increasing protection against cable aging due to temperature extremes.  Polyurethane also offers the flexibility and anti-sag characteristics needed when cables are improperly deployed or installed at unusually low temperatures.

Ruggedized standards also serve to minimize problems arising in pre-terminated OSP assemblies.  These assemblies must not only withstand environmental conditions like other distribution equipment, but they are also heavily handled.  Ruggedization, in particular, is critical for up-jacketing—the process where the 250um fibers of a ribbon or loose-tube OSP cable are furcated to 900um, 2mm, or 3mm—used in the legs of an assembly.