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Dramatic Attenuation in Fiber Access Terminals at Low Temperatures

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It is common in applications where access terminals are used to terminate only a portion of the fibers brought into the enclosure–allowing the remainder of the fibers to pass through. When loose tube cable is used, the sub-units that are not terminated are "expressed" through, and the sub-unit material is not opened at any point. To provide customers with adequate sub-unit length for splicing under all conditions, ADC specifies a mid-span access length of 150" to 170". Testing of the enclosure with expressed sub-units of this length alerted ADC to potential low temperature issues | OmniReach FTTP Solutions white paper Dramatic Attenuation in Fiber Access Terminals at Low Temperatures The Situation It is common in applications where access terminals are used to terminate only a portion of the fibers brought into the enclosure-allowing the remainder of the fibers to pass through. When loose tube cable is used the sub-units that are not terminated are expressed through and the sub-unit material is not opened at any point. To provide customers with adequate sub-unit length for splicing under all conditions ADC specifies a mid-span access length of 150 to 170 . Testing of the enclosure with expressed sub-units of this length alerted ADC to potential low temperature issues. While there are no written standards governing this application ADC has concluded that in some - but not all - cases loose tube OSP cable dielectric or armored can experience excessive attenuation loss at low temperatures 0 C to -40 C . Subsequent research also reveals that the issue becomes more severe for cables exposed to initially high temperatures greater than 50 C prior to their exposure to low temperatures. Attenuation loss can be as high as 10 to 20 dB in extreme cases. After identifying the problem ADC proactively began researching the probable cause and discovered information from a 1998 Bellcore white paper that outlined similar problems with certain fibers in varying temperature environments. The paper entitled Time- and TemperatureDependent Material Behavior and Its Impact on Low-Temperature Performance of Fiber Optic Cables by Osman S. Gebizlioglu seemed to address the very issue ADC was observing in several of its own case studies. According to the paper a series of service-affecting field failures in cold weather -40 degrees C to 0 degrees C initially and in more moderate conditions up to 15 degrees C recently have raised concerns about the temperature-dependent transmission performance of loose tube fiber optic cables. The effect was transmission loss resulting