Keeping fiber reliable for over 50 years

By Brian G. Risch / Prysmian Digital Solutions North America

A fiber network's operational lifetime depends as much on cable materials as on the quality of the optical fiber itself. Optical fiber coatings, buffer tubes, and outer jackets must preserve mechanical and optical performance over decades of service, typically across typical operational temperatures of -40 °C to +70 °C, and under varying humidity, UV exposure, and handling. 

Research into lifetime performance shows where failures originate and how small attenuation increases accumulate when cables face heat or moisture over long periods. 

I’d like to share some insights into the main degradation mechanisms, how industry standards translate reliability into measurable criteria, and how important design characteristics underpin a 50-year service life.

How fiber cables degrade

Multiple environmental issues cause fiber cables to degrade over time:

· Thermal degradation (hot, dry environments): Sustained high temperatures drive oxidation and chain scission in polymer components: jackets, buffer tubes and fiber coatings. The result: embrittlement, loss of flexibility and micro-cracking.  As materials stiffen and crack, more stress can be transmitted to the glass, increasing the likelihood of micro- and macro-bending.  Both mechanisms can increase optical attenuation, possibly to levels that interrupt network functionality.

· Hydrolysis (hot, humid environments): Water chemically reacts with susceptible polymers, notably some acrylate-based coatings and PBT, causing softening, swelling or breakdown. With mechanical changes in the materials, stresses can be transmitted to fibers, again increasing attenuation.  If sheathing is damaged or sealing is inadequate, water ingress accelerates hydrolytic attack-an acute concern for underground, coastal or tropical deployments. Effective water-blocking and robust sheath integrity are critical to long-term performance.

· Coating delamination (adhesion loss): Prolonged exposure to moisture or the secondary effects of thermal aging can weaken the bond between the glass and the primary optical fiber coating. Reduced adhesion can allow the glass to delaminate from the coating, promoting micro-bend-induced attenuation. Delamination can also show up during field work: declining strip force during splicing is a practical warning sign. Optical Time Domain Reflectometry (OTDR) can reveal localized loss features indicative of this failure mode.

Networks experience combinations of these factors, so robust qualification requires multi-stress test regimes including dry-heat aging, humidity cycling, and water-soak evaluations, to prove structural integrity and optical performance remain within limits over decades.

ANSI/ICEA S-122-744 requirements

The ANSI/ICEA S-122-744 standard for outside-plant optical-fiber cables does not mandate a specific lifetime.  Instead, it translates “fitness for long-term service” into performance-based requirements and test methods.  These performance requirements cover attenuation limits, temperature cycling, tensile loading, bend radius, resistance to water penetration and UV exposure, as well as fiber identification, and other physical characteristics. 

Combining dry-heat and humidity aging with kink testing shows that, when appropriate coating systems and cable constructions are used, products can continue to meet the same S-122-744 criteria even after simulated exposure equivalent to more than five decades in harsh conditions. Duration and temperatures required for the 50-year lifetime simulation are determined using the Arrhenius equation.  In these studies, attenuation, strip performance and material integrity remained within the specifications required of newly manufactured cables.

Design principles for 50-year performance

There are multiple design principles network designers should consider to get the most out of their fibers:

• Chemical compatibility: All constituents—glass, primary coatings, tube compounds, strength members, inks, and jackets—must remain compatible over time. Aging must not trigger embrittlement, swelling or adhesion loss.
  
  
• Thermal stability: Materials should tolerate extended high-temperature exposure without degrading and maintain consistent optical performance across –40 °C to +70 °C. Thermal cycling must not cause cracking, shrink-back or stress transfer to fibers.
  
  
• Hydrolytic resistance and adhesion: Primary coatings need durable glass-to-coating bonds, so strip force and splicing behavior remain within specified thresholds after aging. Resistance to water-induced softening minimizes micro-bending and long-term loss.
  
  
• Mechanical durability: Buffer tubes, jackets and strength members must retain tensile strength, elongation, and bend performance after decades of thermal and humidity cycling. Designs should resist handling-related failures such as kinking and cracking.
  
  
• Environmental protection: UV-resistant jackets should maintain mechanical properties and the clarity of printed markings after thousands of hours of exposure. Water-blocking and sealing must prevent ingress in both new and aged states.
  
  
• Stable identification: Fiber colors, tube codes, and all printed information must remain legible after heat, humidity, and abrasion to support installation and maintenance throughout the cable’s life.
  
  
• Optical stability: After accelerated aging, water immersion and temperature cycling, attenuation at 1310, 1550 and 1625 nm should remain within industry-accepted thresholds.