Hakan H. Yuce

Theory and measurements for predicting stressed fiber lifetime

The theory behind experiments used in evaluating fiber parameters needed in the prediction of fiber lifetime is given and the theory is put into a general and unified perspective. Demonstrations are given of how measured parameters may be utilized in new equations to calculate lifetime for a fiber under constant stress. Then an experimental program is outlined in which both static and dynamic fatigue data are analyzed for commercially available fibers. The resulting parameters are obtained for several environments and geometries and are used for lifetime predictions for various deployments.

Optical Fiber Corrosion: Coating Contribution to Zero-Stress Aging

Critical mechanical properties of optical fibers are high strength, small strength variability, high fatigue resistance and high aging resistance. The effect of zero-stress aging on optical fibers is of considerable importance in cables and in splice cases because fibers can encounter high humidity or water which can degrade their strength. These aged fibers may be stressed later during routine maintenance or other field craft activity. The effect of aging on the mechanical reliability of optical fiber is therefore an important consideration in any system design.

Room temperature strength degradation of optical fibers

The strength degradation of lightguide fibers has been studied over a range of elevated temperatures and at room temperature. Using these data we show that accelerated testing can be used to predict ambient temperature behavior. An activation energy of approximately 90 kJ.mol-1 describes the shift in corresponding times.

LIGHT GUIDE FIBERS: PROBLEMS AND PROSPECTS

The authors discuss the new insights and instruments that allow glass researchers to understand, predict, and improve fiber behavior and lifetimes.

Intrinsic strength of light guide fibers

The intrinsic strength ((sigma) i) is defined as the strength in the absence of slow crack growth or fatigue. It is of general interest in the study of brittle fracture, but it is of particular importance in the evaluation of lightguide fiber lifetimes since it is required for the calculation of the constant B. In this work we review the existing literature relating to the inert strength, indicate the limits that can be proposed for and suggest possible approaches to more satisfactory estimates of value(s) of (sigma) i. It is suggested that reasonable values of the inert strength may be obtained by taking 85 - 90% of the liquid nitrogen strength.

Guest Editorial: Optical Fiber Reliability

This PDF file contains the editorial “Guest Editorial: Optical Fiber Reliability” for OE Vol. 30 Issue 06

Effect Of Zero Stress Aging On Mechanical Characteristics Of Optical Fibers

The long-term mechanical reliability of optical fibers is controlled by their strength, fatigue resistance, and zero-stress aging behavior. Understanding the effect of the chemical environment under zero stress on the subsequent fracture strength of optical fibers is important because optical fibers in service are likely to encounter water and other chemical species while exposed to zero or low stress conditions. To determine the effect of zero stress aging on polymer coated optical fibers, we used several fibers which were coated with various UV-curable polymer coatings. The results clearly showed that the strength, fatigue resistance, and aging behavior varied significantly among these fibers. Strength reduction took place after aging in water. Such reduction was both temperature and time dependent and was also affected by the polymer coating. The initial degradation in strength may be partially or fully recovered through drying. However, the degree of recovery became less with increasing storage time at zero stress. A change in the fatigue resistance of these fibers, which was modified by the coating material, was also observed.

Mechanical reliability of fiber optic splices

Todays feeder applications and future distribution applications call for shorter-length, higher fiber count cables, more splices per kilometer, and increased connectorization. Whapham estimates that five to eight splices per subscriber will be required for a branched distribution and loop network. In addition, splices and connectors in the loop will experience harsher environments than the controlled environment of a telephone central office or typical remote site. In the distribution portion, between the remote site and the optical network unit (ONU), the splices can be subjected to a wide range of temperature and humidity extremes, as can the ONU itself. The increased handling and the harsher environments in the local loop place significant new demands on the performance of optical splices.

Splicing of aged fibers

The deployment of fiber in the subscriber loop will require that an optical fiber network maintain the highest possible level of reliability over time, despite being subjected to extremes of temperature, humidity, and other environmental and mechanical stresses imposed on the outside plant. At the same time, both the initial cost and the ongoing maintenance expenses for loop equipment must be kept low. Fiber in the Loop (FITL) applications will entail increased fiber handling. Cable lengths will be shorter, and fiber counts higher, than has been the case so far in long-distance applications. There will also be more cable sheath openings per unit length of cable and/or fiber, as well as more splicing and connectorization. It may become a common practice that a customer is connected to a cable installed many years earlier. In subscriber loops, cables and fibers will be installed in harsher and more varying environments. Fibers will be exposed to higher humidity and temperature, particularly in splice boxes mounted on building walls, in pedestal cabinets, and in other similar enclosures. Corrosive gases and/or liquids may also be present at some locations and will adversely affect the fibers. The combination of increased handling, greater exposure, and more stressful environments may give rise to a need for new, more stringent requirements for fiber mechanical reliability. These can include increaSed fiber strength, increased aging resistance, and increased fatigue resistance.

Aging behavior of low-strength fused silica fibers

The strength of the long lengths of fiber contained in optical cables is determined by the presence of the few large flaws that are produced infrequently by normal fiber production methods. To investigate the behavior of low strength fiber containing these critical flaws, we have produced a fiber containing many large flaws by passing an as-drawn, uncoated fiber over a wheel coated with abrasive. The effect of aging the low strength fiber at zero stress in either 85° C, deionized water or in high humidity (85° C, 94%RH) has been evaluated using dynamic fatigue in tension. After aging in either environment, the strength is found to increase and flaws are found to grow more slowly than flaws in unaged fibers. Both results show that aging actually improves the mechanical behavior of the large flaws that control the strength of fibers in cables.