Osman S. Gebizlioglu

Self-stripping of optical fiber coatings in hydrocarbon liquids and cable filling compounds

Optical fiber coatings are in continuous contact with filling cornpounds in optical cables. They are also exposed to hydrocarbon liquids (either as cleaning or lubricating fluids) during splicing operations. We observed that hydrocarbon solvents such as toluene, acetone, ethyl alcohol,isopropyl alcohol, and light rnineral oils (in cable filling cornpounds)cause swelling and self-stripping in some dual-coated fibers. A numerical stress analysis for a swollen dual-coated fiber revealed that swelling induces a compressive radial stress and a tensile tangential stress in the secondary coating; both stress components attain their maximum values at the primary/secondary coating interface. The self-stripping process occurs when the energy stored (due to increasing tensile tangential stress at the interface) exceeds the fracture toughness of the secondary coating. This analysis has provided quantitative measures of coating hydrocarbon solvent/filling compound compatibility and will establish a rational basis for compatibility in optical cable filling compound design.

Materials issues in the development and use of lightguide fibers, cables, and components

Lightguide technology is now considered to be mature. Indeed, improvements in all aspects of this technology over the years have been most impressive - multimode to singlemode fiber, electronic to optical amplification and the newest and perhaps the most important: the use of WDM and DWDM technologies. In spite of these striking advances, the very nature of the silica lightguide material poses reliability issues which have not yet been fully resolved or in some cases even confronted. These issues by and large have to do with the intrinsic brittle nature of the glass material. In order to assure reliable performance of these lightguide fibers in telecommunications service environments, coating and cabling technologies developed over the past two decades have evolved to give robust fiber optic cables, devices and components. In this presentation, we review key materials issues in the development and use of lightguide technology in telecommunications. Furthermore, we analyze current trends and discuss major materials reliability issues that need to be resolved for further developments in future applications of optical fibers, fiber optic cables and fiber-based components.

Reliability characterization of UV-curable adhesives used in optical devices

UV (ultra-violet)-curable adhesives were identified as the underlying cause for failure of devices subjected to accelerated aging conditions. These adhesives must be resistant to degradation and dimensional/mechanical instabilities such as creep. We examined two UV-curable adhesives and found that thermal post-curing caused some shrinkage and degradation. However, post-curing also raised the adhesive glass transition temperature, thereby reducing the reliability risk associated with mechanical instability. We investigated the dimensional/mechanical stability of UV adhesives by measuring thermal expansion/contraction and creep compliance. We found that the adhesive thermal expansion and creep compliance are large enough to pose device reliability risk. Raising the glass transition temperature of UV-curable adhesives by thermal post-cure can improve optical device reliability by lowering the creep compliance.

Reliability characterization of adhesives used in passive optical components

The number of passive optical devices, connectors, and splices used in optical fiber systems to the home and work place is increasing at an accelerating rate. The extent to which the manufacturing and packaging of these components relies on heat-curable epoxy-based and UV- curable (epoxy acrylate or urethane acrylate-based) adhesives is unprecedented in the telecommunications industry. The use of these materials introduces new reliability issues which must be resolved; the most important of these is the ability of the components to function satisfactorily for long periods of time under adverse environmental conditions.

Refinements and optimization of optical networks toward meeting the bandwidth challenge

In this month?s Optical Communications Series (OCS), we have selected contributions addressing developments in services toward meeting the continuing growth in bandwidth demand. As the global economy?s slow recovery continues, we receive news/announcements of service provider and supplier initiatives addressing the brisk pace of global demand growth for Internet, video, TV, and telecommunications services. Moreover, national and local governments continue to develop programs and policies, such as the U.S. Federal Communications Commission?s ?Connecting America? initiative, to facilitate availability of broadband communications services. As telecommunications networks continue to develop, optical communications technologies promise to enable truly broadband communications-based services in such applications as long-distance education and tele-medicine.

Low-temperature performance of loose tube fiber optic cables

Some recent service-affecting field failures in cold weather raised concerns about the low- temperature performance of loose tube fiber optic cables. These failures occurred predominantly in aerial transmission lines operated at 1550 nm. Field OTDR (optical time domain reflectometry) analyses and laboratory measurements established that the increased attenuation at low temperature resulted from fiber microbending caused primarily by the thermal contraction of buffer tubes. Cable structure tightness based on a model of mechanical coupling between cable elements and excess fiber length-to-buffer tube inner diameter ratio emerged to be two key parameters to control the magnitude of this temperature-induced cable loss (TIC). Based on our analyses, we developed a clamping device for re-termination of affected cables in the telecommunications network.

Low-temperature transmission loss in loose tube fiber optic cables

Large optical losses in singlemode fibers have been reported in loose tube fiber optic cables exposed to extremely low temperatures (-20 degree(s)C to -40 degree(s)C). These losses have occurred predominantly at 1550 nm (although some transmission systems at 1310 nm have also been affected) in aerial cables and were confined to the cable section adjacent to a splice closure. Optical transmission measurements on commercial fiber optic cables that were subjected to temperature cycling in an environmental chamber indicated that thermal contraction of buffer tubes at low temperature was the major contributor to fiber bending-induced loss. While the buffer tube thermal shrinkage occurs, optical fibers contained in the tube undergo nearly zero contraction. Consequently, the fibers buckle against the buffer tube inner wall, causing bending-induced losses. Cables with an initially low fiber excess length-to-buffer tube inner diameter ratio, and strong buffer tube-to-central member coupling exhibit minimal loss. It has been demonstrated in the laboratory that the low-temperature optical loss can be suppressed by effective coupling of the cable sheath to the central member.

Field measurements of PMD using four measurement techniques

In the last 10 years, Telcordia has conducted numerous first-order PMD (polarization mode dispersion) measurements of installed optical fibers at various locations throughout North America. The measurements were made by using test instruments based on interferometric method. This work has been reported in detail in the past NFOEC symposia. The results have been analyzed with respect to various cable designs, type of outside plant, year of manufacture, and cable manufacturers. Recently, Telcordia has had the opportunity to make additional PMD measurements on previously characterized optical fibers. The new Telcordia measurements were made by using test instruments based on four measurement techniques. The recent PMD measurements include equipment that uses the following PMD measurement techniques: wavelength scanning (fixed analyzer) with cycle counting, Jones matrix eigenanalysis, wavelength scanning (fixed analyzer) with Fourier transform, and interferometry. According to TIA (Telecommunications Industry Association) inter-laboratory round-robin PMD tests, the four methods above yield systematic and random disagreement between measurements of within /spl plusmn/ 10 % to /spl plusmn/ 20 %. This variability is stated as state-of-the-art by TIA/EIA in their FOTPs (fiber optic test procedures) describing PMD measurement methods. The new Telcordia PMD measurements are expected to provide significant additional insight as to the relationship between the four PMD test methods listed above and help contribute to the general understanding of the major approaches to modern PMD measurement techniques.

An Overview of Fiber-to-the-Premises (FTTP) Product Requirements and Qualification Programs

North American deployments of FTTP architectures have been rapidly increasing. While the FTTP market is being driven by major telecommunications service providers, equipment suppliers have been scrambling to bring products to market that will ensure them a piece of this high-stakes market. In this invited presentation/paper, we propose to examine the technical requirements that are needed to support the new FTTP network with a host of new products that have been in development. To enable service providers select the best new products for FTTP deployment, product selection needs to be based on the analysis and testing of new products for performance and reliability, Telcordia, in its traditional role of telecommunications standards development, has been publishing generic requirements (GR) documents that have been used by suppliers, service providers and the industry at large. Product qualification programs based on the established performance and reliability requirements/standards have been designed to evaluate products to determine if they can 1) withstand the rigors of the outside plant deployment environment and perform for extended periods of time, 2) be upgradeable, and 3) craft friendly. The outside plant is a tough environment to live in. A product must perform under the extreme conditions of cold down -40°C (-40°F) and hot up to 46°C (115°F) with high humidity of 95%, rain, snow, sleet, vibration due to traffic, lightning, heating due to solar loads, high winds, ice, sand storms, and products are even tested to demonstrate if they can continue to operate in an earthquake, a wild fire and a shotgun blast. All FTTP products are not only expected to perform, but they must meet stringent optical performance criteria of low insertion loss and reflectance / return loss at a broad range of wavelengths from 1310, 1490, 1550 and 1625 nm. While the upstream (from the customer to the CO) voice and data transmission is currently planned over 1310-nm wavelength, the downstream (from the CO to the customer) voice and data transmission is offered over 1490 nm, the video (analog, digital and HDTV) transmission will be offered over 1550-nm wavelength, and the 1625-nm will be reserved for overhead, surveillance, and management functions. This paper will cover some of the new products that will be needed and the requirements that would apply. The FTTP deployments require the placement of a number of new products in the FTTP network from the CO to the customer premises. These new products are designed to be installed in an efficient manner with acceptable cost to the service provider in the outside plant and to perform the required functions. One such new product is an HFOC (Hardened Fiber Optic Connector). The HFOC products provide drop connections to customers from fiber distribution networks. They may be placed in pedestal closures, aerial and buried closures, or equipment located at a Fiber Distribution Hub (FDH) enclosure or optical network termination (ONT) unit near customer premises. Current versions of this HFOC product have been based on a well-known and widely used SC fiber optic connector. Simply described, it consists of an SC connector in a protective shell made of a polymeric (plastic) material, and it allows highly efficient connections between the distribution cables from the FDH (Fiber Distribution Hub) where optical signal on a feeder cable from the CO is split for transmission over distribution cables and drop cables in locations near customer premises. In addition to the description of new products, the paper will review the environmental, mechanical and optical test criteria. Attendees would benefit from the knowledge of products and requirements needed to support FTTP deployment.

An overview of fiber failures in cables and interconnecting devices

Failure analysis of fiber optic cables, components and devices from manufacturing operations, installation and field deployment has been important in reliability assurance for fiber optic communications networks. In this overview presentation, we consider optical fiber transmission failures in fiber optic cables and optical transmission impairments accompanied by mechanical failures in cable assemblies and interconnecting devices. In either case, failure analyses involve detailed characterization of optical and/or mechanical performance under varying environmental conditions such as temperature and humidity. In the case of optical transmission failures of fiber optic cables, we show that the environmental history of the cables and the thermomechanical response of buffer tube materials are of critical importance in understanding low-temperature transmission loss due to thermally-induced fiber microbending. In optical transmission impairments accompanied by fiber mechanical failures of cable assemblies and interconnecting devices, the environmental history along with manufacturing practices used in the production of cable assemblies determine the performance and reliability in the field. For cable assemblies with fiber mechanical failures, fiber break source analysis (fractography) has many challenges in the analysis of fiber breaks where fiber fracture surfaces are readily accessible. However, it has been practically impossible to perform break source analyses in cases where fiber fracture surfaces are not accessible within cables and interconnecting devices. Thus, in this presentation, we review a series of failure analyses performed to identify the cause(s) of high insertion loss and reflectance failures of cable assemblies. An essential component of these failure analyses was the development of new methods for accessing fracture surfaces of broken fibers within connectors. These new methods involve chemical and thermal treatments to preserve all features of fracture surfaces and, therefore, evidence of failure origins.