This paper describes a novel and efficient method for parameter extraction and characterization of Erbium-doped fiber amplifiers (EDFA). In DWDM systems gain and noise behavior of EDFAs depend on the number and distribution of transmission channels. Hence, characterization of EDFAs for reliability evaluations requires a costly measurement setup of up to 80 or even more wavelength selected laser sources. Our novel method uses photonic transmission simulation to drastically reduce the measuring efforts. Using only a few characteristic measurements with one tunable laser, the gain and noise behavior of amplifiers can be simulated for any number and distribution of transmission channels in DWDM systems. The simulation of the photonic transmission is based on the commercial simulation package WDMTransmissionMaker by VPI systems. We utilize black-box models for fiber amplifiers which can take into account all linear optical effects like e.g. gain-flattening filters or dynamic gain equalizers. The predictions of the simulations for different single-stage as well as double-stage amplifiers comply with the experiments within the measurement accuracies and help to understand new up-coming optical amplifier technologies and to ensure more reliable optical system designs. The measuring effort for qualification and reliability evaluations can be significantly reduced by using the novel characterization method.
This paper describes analysis tools and characterization techniques for photonic components related materials analysis as well as functionality and reliability testing. Field failures and breakdowns of optical fibers and cables, fiber Bragg gratings, connectors, semiconductor lasers, opto-couplers, micro-optical elements, and others have to be analyzed and failure causes and mechanisms have to be found in order to improve future components. On the other hand, new materials used and new components for future all-optical networks may lead to new failure mechanisms, which have to be analyzed and modeled for lifetime predictions. In this paper some basic principles of instruments and techniques used for reliability and failure analysis rather than a deep treatise are given and may guide the reader to find appropriate methods for a specific problem. Illustrative examples are provided.
For the extension of existing optical fiber links to higher data transfer rates in the multi-gigabit range and the expected higher power density due to DWDM one must consider possible limitations of the deployed cables. Many investigations have identified polarization mode dispersion PMD as a crucial parameter especially for cables exposed to environmental stresses. Three aerial optical fiber cable links were characterized by measuring PMD, optical time domain reflectometry OTDR, polarization-OTDR, and bit error rate BER. Measurement results over several days are correlated to temperature data from weather stations along the cable lines.
The reliability and the expected lifetime of silica fibers are closely related to the chemical action of water molecules on silica. Strength and dynamic fatigue behaviour of silica optical fibers were measured in very dry atmosphere. Bare and coated fibers were compared to characterize the influence of the polymer. Dynamic mechanical tests were implemented using a two point bending set-up. The stress corrosion susceptibility parameter has been evaluated. At the higher stressing rate the slope of the dynamic fatigue curve was found to drop significantly. This behaviour is usually observed for specially damaged fibers tested at very high speed.
The strength of silica optical fiber is closely related to the activity of water at its surface. However, observations have shown that the polymeric coating is also a key factor contributing to the mechanical properties of the fiber. While the main role of the coating is to inhibit crack growth from the surface Griffith flaws, it also reduces the water concentration at the glass surface through diffusion processes.
Dynamic and static mechanical tests were implemented using a tensile test bench and a static fatigue test under uniform curve. The incidence of aging treatments at 65°C and 85°C was investigated on two standard silica optical fibers (with polyacrylate and fluorinated coatings). Fatigue under static tension was also investigated using a vertical static tensile bench.
Microscopic observations helped the understanding of the failure mechanism. It appears that the cyclic variations of the failure stress phenomenon, with respect to the aging time, are the result of the silicate gel which migrates towards the polymer coating.
The past decade has seen a huge increase of demand for fast data communication; this stimulated the optical research towards the design and development of both terrestrial and submerged long-haul full-optical transmission systems. More specifically, the submarine systems are required to be highly reliable: minimum lifetime of 25 years with very low maintenance, which implies the request for long term reliability for each component. In this work a reliability estimation approach based on hi-rel optical component degradation study is discussed. Results of a long-term test performed on optical isolators for submarine applications are reported. The experimental optical bench set-up, based on switching matrixes, developed at Pirelli Reliability Labs is also presented.
Pyrolytic carbon coatings show excellent hermetic properties and can be applied to optical fibers during the draw process by thermally activated chemical vapor deposition (CVD). This study investigates the relationship between carbon growth rates, microstructure, and deposition conditions at 600 torr chamber pressure. The films are grown from methane, propane and butane precursors on stationary 3 mm quartz rods. Hydrocarbon precursor gas concentrations are varied between 10% and 100% in N2, and surface temperatures are varied between 800 and 1500°C. X-Ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), and Secondary Ion Mass Spectroscopy (SIMS) are used to determine the film composition, and to inspect for a SiC transition layer between the carbon and the glass. The carbon films are analyzed for thickness, carbon phase, and surface roughness using ESEM and Raman Spectroscopy.
In recent years reliability has become a key topic for network providers because of the increasing complexity and economic importance of their systems. In order to avoid high costs resulting from downtimes of the system and maintenance it is mandatory to include reliability considerations already in the design of networks. This requires a precise knowledge of the expected lifetime of the components of the network. A method for the quantitative assessment of the reliability of passive fiber optic components is described in the IEC standard 62005-2, Part 2.
In this paper, we present the reliability assessment of planar fiberoptic 1x8-splitters as an example for the application of the above mentioned IEC standard. The failure rates resulting from wear out mechanisms are determined by a life test matrix with accelerated aging induced by extreme climatic conditions and extrapolation to service conditions. With 6000 hours under 85°C/85% r.h. without any failure the tested components also exceed the requirements given in Telcordia GR 1221. In addition to climatic tests, vibration and impact tests have been performed in order to prove the mechanical integrity of the splitters.
A second failure class besides wear out failures are random failures which occur at a constant rate. Due to the nature of random failures they can not be accelerated in any kind of laboratory tests. Thus the random failure rate of the components is calculated from field data. The observation of 16,000 devices with a total of more than 300 million service hours shows a FIT-rate for random failure which is below 10 FIT.
The impact of silica glass structure on the transmission properties of Ge-doped single-mode optical fibers was studied. Test fibers with significantly different fictive temperatures (Tf) and residual stresses were drawn by varying cooling rate. Tensile or compressive residual stresses were achieved in core of the fibers. The results show that: (1) Both residual stress and Tf have an impact to the transmission properties, in particular, the stress in core. (2) A greater complexity was found in the relationship between transmission properties and glass structure than has been shown earlier. E.g. Rayleigh scattering was found to decrease and loss imperfection factor to increase with increasing Tf within one of the fiber series. Thus Tf can not alone be used to characterize the fiber glass structure. (3)Rayleigh scattering is dependent on both Tf and residual stress, in particular on core stress and probably on the structure of core glass. A relatively low Rayleigh scattering was found in fibers with Tf as high as 1600°C. (4) Zero dispersion- and cut-off wavelengths are modified by residual stress.
The strength of optical fiber at low temperature is an important parameter since it approximates the inert strength, i.e. the starting strength of the material before degradation by fatigue. Published data suggest that the fatigue may abruptly slow below some temperature. However, published data are limited to strength vs temperature or fatigue in liquid nitrogen. We report strength and fatigue data for both bare (stripped) and metal coated fused silica optical fiber at temperatures down to 77 K. While fatigue slows as the temperature is reduced (i.e. the stress corrosion parameter increases with falling temperature) fatigue is still measurable at 77 K. This is the case even for hermetic metal coated fiber with extremely low water activity at the glass surface. The results confirm that fused silica exhibits "intrinsic" fatigue, i.e. fatigue in the absence of moisture.
This paper reviews the dependence of strength and fatigue of fused silica optical fiber on the environmental parameters temperature, humidity and pH. It is shown that the stress corrosion parameter, n, is not a constant but depends on the nature of the environment. Further, different kinetic forms for the stress corrosion kinetics lead to different interpretations of experimental results. Since lifetime predictions are very sensitive to the value of n and the kinetic form, it is important to know which form is correct. It is shown that the empirical power law form that is almost exclusively used by the fiber optics industry provides a good fit to fatigue data for high strength fiber, but an exponential form provides a more self-consistent description of fatigue in different environments.
In this paper we present a brief historical review, including a discussion of some of the advances we think have been made in the area of mechanical reliability of lightguide fibers. Fatigue and aging of these fibers are reviewed in detail. It is shown that these processes are fundamental to the silica glass itself, at least under normal environmental conditions. It is suggested that the single most important outstanding issue is the determination of the presence of fatigue and/or aging limits. If these limits are shown to exist in general, or at least under certain conditions, a major simplification of lifetime analysis will have been accomplished.
Fluoride glass fibers are used for various passive and active applications. Current fibers are made from fluorozirconate glasses. Their intrinsic strength is smaller than that of silica fibers and their surface may be damaged by liquid water. The discrepancy between the reported values of the fiber strength reflects the major part of the extrinsic defects in the failure mechanism. The surface of the glass preform determines fiber strength to a large extent and numerous defects are induced during fiber processing. These defects are largely correlated to the chemical action of water.
Dynamic fatigue measurements have been carried out. They show that the average strength depends on fiber length even though when a proof test is made prior to measurement. Fiber strength is not constant for all fiber segments originating from the same preform. Atmospheric humidity also influences fiber strength and dried fiber show much larger failure stress. Aqueous solutions corrode surface fiber resulting in the significant decrease of the fiber strength. Structural relaxation may occur in fibers under stress inducing permanent bending and reduction of applied stress. Fibers hermetically packaged are more reliable and some of them have been used in outdoors conditions for years. While surface has to be protected from water in any case, controlling extrinsic defects should lead to the large improvement of the fluoride fiber strength.
Optical fibers are susceptible to catastrophic damage at relatively low optical powers of less than 1 watt. This threshold, exceeded by several times, and in some instances by a factor of ten in today’s amplified wavelength division multiplexed optical communication systems, poses a dormant problem for many optical devices, fiber-connectors and optical fiber links. This paper presents perspectives on this issue based on research performed on the subject.
The technology of tomorrow's telecommunication networks will be flexible, scalable and integrated. In addition, there is a visible trend towards purely optical networking to avoid costly electronic regeneration. The move towards optical networking drives the development of new optical components to exceed current technical and physical boundaries. These new optical components include Photonic Optical Cross-connects (PXC) and Tuneable Lasers (TL), which can be realized by Micro Electro-Mechanical Systems (MEMS) based technology. MEMS technology allows the integration of optical switches with very high density. At the same time introducing MEMS technology is a step back from having no moving parts to mechanics. The trade-off between the risks and the advantages must be addressed. Typical optical requirements for the function of MEMS based technologies are introduced, and a strategy to prove the reliability is shown.
A brief overview of some possible degradation mechanisms of Raman amplifiers and lasers is presented. It is demonstrated that further investigations are required to clear up all the open questions related with mechanical and optical reliability of such devices and their components.
Fiber optic sensors are potentially very well suited for condition monitoring of environment, materials, structures, and facilities. However, there is a long way from a laboratory prototype to a reliable industrial sensor system. Based on the examples of two fiber Bragg grating systems, both used for long term monitoring of strain and temperature on bridges, general sensor system reliability will be discussed. In addition, specific reliability considerations and lifetime tests, especially for optical fibers and Bragg gratings, coatings, and adhesives will be presented.
Swisscom Fixnet Ltd. has evaluated a new platform for the broadband transport requirements. This new platform will be a combination of advanced SDH (Synchronous Digital Hierarchy) and WDM (Wavelength Division Multiplexing) technology and the principal goal is to cover the bandwidth segment between STM-1 and STM-64. In addition new forthcoming data services e.g. Gigabit Ethernet can be delivered on the same platform infrastructure between remote areas. This paper describes the drivers for the project as well as the requirements at the start of the evaluation process of the transport platform. The requirements include technical, operational and financial aspects. The main focus will then be the discussion of the core, metro or regional area architecture. Various scenarios have been analyzed and compared. The main conclusions have been that the number of "flexibility points" should be kept lower than in traditional SDH-network due to cost reasons in a broadband environment with packet oriented services. Furthermore, the WDM technology is not economically reasonable for a low number of channels in the regional area. The paper then summarizes these lessons learned from the project.
Free space optics (FSO) is a high-speed point-to-point connectivity solution traditionally used in the enterprise campus networking market for building-to-building LAN connectivity. However, more recently some wire line and wireless carriers started to deploy FSO systems in their networks. The requirements on FSO system reliability, meaing both system availability and component reliability, are far more stringent in the carrier market when compared to the requirements in the enterprise market segment. This paper tries to outline some of the aspects that are important to ensure carrier class system reliability.
Highly reliable and available systems in all-optical networks require the implementation of various types of redundancy. For reliability and availability analysis systems can be described by reliability block diagrams or diagrams describing system state transitions. Analytical calculations for characteristic reliability and availability parameters such as mean time to failure or average availability for complex, repairable systems containing redundancies rapidly become costly and intractable. Monte Carlo simulation and Markov process calculations are therefore deployed. Results of simulations and calculations show sufficient accuracy and high flexibility for sensitivity analysis. Sensitivity analysis is the quantitative identification of system parts dominating the overall system availability by systematical variation of calculation input data, i.e. failure and repair rates. This gives valuable input for possible system optimization comprising technical and economical aspects.
This contribution investigates mean time to failure, mean unavailability and mean down time of an optical cross connect described by a complex reliability block diagram. In addition a sensitivity analysis is performed. All Monte Carlo simulations and Markov calculations are done by using a commercial software tool.
Stress corrosion factors were obtained for the waist region of a fused fiber component using the dynamic fatigue method at ambient temperature and humidity. The n-value obtained is 23.3, which is comparable to that of pristine fiber. The ultimate tensile strength of the waist is much higher than that of the mechanically stripped fiber used to manufacture the components, indicating that flaws and defects are actually repaired during the fusion process. Component lifetime and reliability are estimated.
The Chalcogenide glasses offers a range of infrared transmitting materials to the optical fiber technology and this review attempts to bring together the currently available data on the mechanical properties of these fibers. Information is presented on glass composition and mechanical qualities, mechanical characterization techniques, and coating technology. Different studies have shown that changes in composition have little influence on mechanical properties of Chalcogenide glasses, and so other techniques will have to be employed in order to improve the mechanical performance. Among those techniques are compressive surface stress and multi-coating polymers.