A framework of one basic lifetime model for optical fibers with an alternative for on-line proof testing, and with a choice of three test methods for the weak flaw distribution as input, is given. For the first time the effect of zero stress aging (in water) is taken into account. An analytically soluble lifetime model is obtained using a description of combined stress corrosion (power law) and zero stress aging with the `blunt pit' model, assuming blunt weak flaws (worst case). Aging results in a decrease of allowable service stresses by a factor of two for the treated numerical example. The Haslov/Jensen model is also treated for comparison.
An atomic force microscope (AFM), operated in both contact and tapping mode, was used to study fractured polymer/silica optical fiber interfaces. The polymer coating was separated from the fiber either by pulling the fiber out of the coating or via delamination through immersing the coated fiber in an organic solvent. The fracture surfaces were analyzed by comparing the resultant surface topography with the polymer removal procedures. The AFM analyses suggest that the fracture process is sensitive to the cohesive properties of the polymer, as well as the adhesive bond strength of the interface. We demonstrate the utility of an AFM to study adhesion of viscoelastic polymers to silica surfaces.
Aging uncoated pristine silica fibers in the vapor of hydrofluoric acid results in the formation of spatially resolved surface etch pits as determined by atomic force microscope images, and mechanical strength reduction. Modeling the strength controlling flaws as partially embedded hemispheres results in good agreement of measured and calculated strength.
At temperatures higher than 400 degree(s)C the decrease of aluminum coated fiber strength due to interaction between glass and aluminum was observed. The rate of this decrease appears to depend on the interface between glass and metal. The influence of atmosphere above the metallizer at the application of a metal coating by the freezing method was investigated. Some decrease of the initial bending strength, yet longer lifetime at high temperatures, have been observed for fibers sealed in atmosphere containing oxygen, which can create an alumina layer between silica glass and aluminum. In order to exclude the chemical reaction between silica and aluminum, an intermediate layer of carbon was applied during the fiber drawing. Results of the carbon coating influence on strength and lifetime of aluminum coated fibers at high temperatures are presented.
Fiber ribbons provide compact, cost effective packaging of optical fibers. In a fiber ribbon cable, individual fibers can be easily identified and accessed. Fiber ribbons can also be considered as an intermediate cabling structure. We given an overview of fiber ribbon cables, fiber ribbons, and discuss reliability related issues and test procedures.
We have shown in previous work that the addition of small quantities of colloidal silica to the UV- curable polymer coating of fused silica optical fiber causes a dramatic improvement in the fatigue and aging resistance both in aqueous and in constant humidity environments. The presence of silica in the coating inhibits the mechanisms responsible for the surface roughening that causes the fatigue knee and strength degradation during zero-stress aging. This work presents results which show the effect of higher concentrations of the silica additive (6 wt%) and of an adhesion promoting agent on both the rheological properties of the polymer coating and the fatigue and zero-stress aging behavior of the fiber. Viscosity measurements show thixotropic behavior which indicates that the silica particles tend to form a network structure in the prepolymer. Filtration of the prepolymer to remove large particles is hampered by this phenomenon. The fiber coated with the silica-containing polymer exhibits substantial improvement in the long term mechanical reliability compared to a reference fiber without additive in the coating.
Examination of the surface profile of silica optical fiber using the atomic force microscope (AFM) has proved a useful technique for understanding strength degradation of the fiber upon aging in aggressive environments in terms of the production of surface roughness. However, before AFM examination it is necessary to remove the polymer protective coating and this is usually achieved by dipping the fiber sample in methylene chloride (MeCl) or hot (approximately 200 degree(s)C) sulfuric acid. This raises the possibility that the stripping technique modifies the fiber surface. In this work it is shown that hot acid stripping does not affect the fiber strength. It does, however, remove a surface layer from the aged fiber, probably of hydrated silica, which does not contribute to the strength. Therefore, treatment with hot acid is necessary in order to reveal the strength controlling surface profile, even if there is no polymer coating requiring removal. MeCl does not remove the surface layer and does not reveal the strength controlling surface.
The influence of the chemical environment on the lifetime of fiber with a standard polymer coating is studied with fatigue tests. Tests were performed in ambient air, water, ammonia, acidic and basic solutions. The diffusion of reactive components in the coating material appeared to be of considerable importance for the measured lifetime. Small amounts (2 wt%) of additives (acids, amines) were used in the standard coating material. Various additives are shown in fatigue tests to have a large negative influence on the lifetime of the fiber. One additive has a large positive influence. Possible mechanisms are discussed.
Fiber optic reliability is increasingly important because of increased telecommunication traffic density and migration of optical fiber closer to the subscriber. An overview is given of what fiber optic standards are, their benefits, where they are generated, and what has been published (or soon will be) on fiber reliability standards. These concern test procedures for measuring fiber reliability parameters, and also concern theory for using these parameters for predicting fiber reliability. We update a previous paper on standards work, concentrating on recent achievements.
The reliability of long lengths of fibers in optical cables is determined by the presence of weak spots which are infrequently produced by normal fiber production methods. It is important to investigate the influence on strength of fiber from different kinds of weak spots. The present study is confined to weak spots resulting from melted-in zirconia particles. Tensile testing of optical fiber, in which strength degrading particles of a roughly dual-size distribution have been introduced on purpose, was done At a wide range of stress rates. The Weibull plots of tensile strength of the fiber were compared with a theoretical distribution, based on a simple relation between particle size and fiber strength. In this way, failure modes could be identified and related to the size of particles. From the comparison it was concluded that the size of zirconia particles has no significant influence on the fatigue of fiber, within the applied stress rates. A significant retardment of the fatigue of weak spots was also observed at low stress rates.
The effects of glass preparation on the surface corrosion of fused silica optical fibers was studied by aging different fibers in both deionized water and tap water at 80-85 degrees C for several months and then analyzing the surface morphology of the samples using atomic force and scanning electron microscopies. We observed that surface corrosion, which causes strength degradation, is related to preparation defects in the glass, these include the existence of glass particles and layers, the presence of impurities and point defects, and in general all locations at which the bond strength is less than that of the Si- O bonds of silica. We found fibers whose surface did not become rough, despite the presence of a corrosive coating. we also find fibers whose surface roughness remained constant during aging in water, due at least in part to the protection provided by the coating. These findings imply that the effects of the glass preparation on the surface corrosion can be minimized through careful attention to the glass and to the fiber manufacturing processes.
A ratio of inert to ambient strength >= 1.5 is suggested for large flaws in optical fiber near the proof stress level. Also, a temperature dependent strength at low temperatures, similar to that observed in pristine fibers, was investigated. An increase in fracture toughness or changes to the crack tip geometry at low temperatures did not account for the increase in strength at low temperatures. Inert strength distributions were predicted from strength obtained under ambient conditions for as-manufactured fiber and fibers with handling damage.
Prooftesting optical fiber is required to assure a minimum strength over all lengths of fiber. This is done as the fiber is wound onto a spool by applying a tensile stress over a length of fiber as it passes a stress region. The failure of weak flaws assures a minimum strength of lengths that survive the test. Flaw growth is assumed to follow the power law. Distributions of initial flaw size are assumed to be of the Weibull type. Experimental data are presented to validate these assumptions.
Optical fibers may experience conditions which are potentially damaging to the protective coatings. They may be subjected to high temperature, high humidity environments, or come into contact with water, solvents, or various household chemicals. It is important that fiber properties such as strip force, coating adhesion, transmission properties, and fiber strength are maintained after exposure to such conditions. Aspects of coating design, and how these relate to fiber reliability, are discussed.
Optical measurement techniques to determine differential longitudinal strain on optical fibers are described. These methods can be applied to cabled or uncabled fiber. Measurements include corrections for stress induced changes in the optical fiber's group refractive index.
Three kinds of UV-curable organically modified silicates have been prepared to be used as protective coatings for optical fibers. The synthesis involves the reaction of the thiol group of 3-mercaptopropyl-trimethoxysilane with a C equals C bond in one of the acrylic groups of three commercially available aliphatic triacrylates. The methoxysilyl groups of the synthesized diacrylate methoxysilanes were subjected to hydrolysis and condensation to form Si-O-Si units. Transparent, viscous, solvent-free resins were obtained that hardened in seconds when exposed to UV radiation. The coating derived from the reaction with glycerol propoxy triacrylate (GPTA) proved to adhere the best of the three to both plastic and glass substrates. It was then tested as a protective coating for silica fibers. Reliability tests were carried out including bending strength and fatigue tests at pH 7 and 10. The results show improved water resistance of the coated fiber in neutral conditions.
In a manufacturing environment data has been collected on the changes in performance of fused biconic couplers due to temperature cycling and due to long term high temperature storage. The average change in insertion loss after 20 temperature cycles from -40 degree(s)C to +75 degree(s)C for a 50% 1X2 coupler is 0.03 +/- 0.025 dB with a standard deviation of 0.1 dB. The average change in excess loss is 0.03 +/- 0.02 dB. Continuous monitoring of coupling ratio while temperature cycling from -40 degree(s)C to +75 degree(s)C showed a variation in coupling ratio of less than 0.5% at the extremes compared to 25 degree(s)C.
Many possibilities are offered to compute field. We have used in this work the bpm method and the local mode method for a conical fiber. In the second case, it is shown by a length-scale criterion that some geometry should provide a good efficiency. We examine the fiber end and show that an appropriate lens form makes it possible to adapt the power distribution between the optical fiber and the photodiode. Some taper shapes are suggested and the model accuracy is discussed according to the nature of the decrease criterion. We obtain in this case an assessment along this guide that is optimized. The comparison of this results with the quasi 3D numerical simulation of the guided optical propagation is also performed.
The prospect of installing couplers into fiber-in-the-loop (FITL) subscriber systems has brought the issue of component reliability to the forefront. It is critical that couplers be deployed in the networks with a high level of confidence. To gain that confidence and to ensure product reliability in different service conditions and over extended periods of time, Corning approaches coupler reliability with an extensive multi-tiered program. A comprehensive approach to gain an understanding of a product's performance capability and its failure mechanisms are obtained and modeled to assess product reliability for its useful lifetime.
The requirements for reliability of optical devices are becoming increasingly stringent. The qualification of new products requires that a variety of tests be performed under a range of severe environmental stress conditions. Results of test programs on an interference filter-based WDM for use in 1480 nm pumped erbium doped optical fiber amplifiers demonstrate that these components can meet existing requirements. With test specifications now requiring test durations of 5000 hours, automated test systems are necessary.
We report accelerated aging tests of nonlinear optical polymer planar waveguides subjected to electron irradiation at doses up to 25 MRad(Si). The decay of the second-order optical nonlinearity of dye-doped poly(methyl methacrylate) films was monitored by second-harmonic generation with the temperature maintained near the glass transition temperature. The results indicate a decreased orientational stability of the chromophores in irradiated PMMA films.
The effects of radiation on the performance of two types of high gain optical detection components of optical LAN systems has been measured. In particular, we have determined the variation of the sensitivity, responsivity, dark current, and noise with radiation in solid state PIN diodes and avalanche photodiodes. We report here on the detailed studies that have been performed.
We have measured the effects of electron and proton radiation on LiNbO3 electro-optical devices. These include waveguides, switches, Mach-Zender interferometers, etc., of both Ti indiffused and proton exchange construction. The effects of continuous and pulsed beam in situ and out of situ were measured.
We have measured the effects of radiation on various long wavelength diode devices using InGaAs technology. The various components were exposed to radiation of continuous electron and gamma beams at the Lehigh University Van de Graaff Radiation Facility and proton beams at the Brookhaven Tandem Facility.
The world that we live in has no boundaries and when a calamity strikes, all nations are immediately informed and volunteer their help. From our experience the restoration of communications systems is the key since it restores connectivity with the outside world and establishes a damage assessment with further identification of needs. In the environmental sector fiber optic sensors technology is widely utilized to detect various hazardous materials and radiation levels. Teleoperated robotic vehicles are used to perform key tasks in contaminated environments such as nuclear power generating plants. This paper addresses the development of a fiber optic video and audio link for adverse environment applications.
Multimode fiber is increasingly being used in high data rate (> 100 Mb/s) systems with both short (< 2 km) and long (> 2 km) system fiber lengths. Obtaining reliable system performance at an economical price in these types of applications requires more precise multimode link design methodologies than previously required for low data rate, short length implementations. The Telecommunications Industry Association/Electronics Industry Association (TIA/EIA) Working Group FO-2.2 generated a draft Multimode Fiber Optic Link Design Standard to address any multimode fiber optic system application up to 500 Mb/s. This paper discusses the approaches used in the draft TIA/EIA Multimode Fiber Optic Link Transmission Design Standard and shows a comparison of the system performance predicted using the standard versus actual system performance for several simple implementations.
Inherent immunity to electromagnetic interference, light weight, and high data capacity, make optically based control systems attractive candidates to replace their electronic counterparts in many mobile platform applications. Additionally, size differences between optical fibers and metal conductors afford optical fiber data busses a reduced probability of sustaining a direct hit from ballistic or maintenance induced impacts. Drawing on techniques used in smart structure technology, this size reduction can be exploited by integrating the optical data bus with the airframe structure to achieve enhanced protection from external stresses. However, due to the brittle nature of optical fibers, a near impact of extreme thermal stresses may be more likely to induce catastrophic damage to an optical data bus. We demonstrate a technique which reduces the static and dynamic induced strain transferred to a structurally integrated optical fiber. Experimental data shows that this method eliminates nearly all fiber strain due to static loading, and greatly reduces the induced strain from a ballistic impact. The analysis shows that relatively small reductions in a constant stress, applied to an optical fiber, results in sizable increases in the predicted lifetime of the optical fiber.
An analysis, and experimental data, of the time-dependent response of an all-fiber ring resonator are presented in which the ring is illuminated by a phase modulated input beam. The resonator is operated as a high resolution scanning spectrometer. Since the resolution limit is a function of the finesse and cavity loop length we show that it is not possible to design a high resolution ring resonator that does not produce a distorted output signal when the phase modulation rate is comparable to the response time of the ring.
This account begins in the wee hours of a bitterly cold night in the winter of '92 - '93. A fiber optic transmission system starts to incur unacceptable errors and switches to a protect channel. The system is being run at 1550 nm because it is a route which is long enough to otherwise require a repeater at 1310 nm. OTDR measurement shows high splice losses. By dawn the high-loss splices have partially recovered so the system is switched back to the original fibers. Failure of the mechanical splices is suspected, the RBOC requests post-mortem assistance from Bellcore, and a team is dispatched immediately to work with RBOC personnel in determining the cause of the failure.
Methods for predicting service reliability of passive fiber optic interconnections have not developed to the same extent as they have for fiber. Much progress has been made in the understanding of failure modes, however, it has not been extended to the estimation of mean life or failure rate as a function of time. The most critical need is the development of appropriate life-stress models which include test acceleration factors and statistical analysis methods. In this paper, simple models are proposed for three distinct failure modes: (1) flexural fatigue of a connector bend limiting assembly, (2) static fatigue of a ceramic connector alignment sleeve, and (3) torsional fatigue of fibers in splices. The more general problem is discussed in the context of these examples.
Although current splices and connectors are proving to be quite reliable there is definite room for improvement. The major issue in reliability is continuing quality assurance of the assembly processes. We need connectors that do not generate debris as they are coupled. Connectors must latch positively and they must retain physical contact throughout the range of environmental conditions to which they are exposed. We also need a better understanding of the processes that determine the reliability of the reflectance performance: bonding of the fibers into the ferrule, and polishing.
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.
The relation of the measuring beat length of a fiber to the working wavelength and environment temperature is described in this paper. Analysis and experimental results show that there is a direct proportion between beat length and working wavelength in different fibers. The measurement results of the relation of beat length to the wavelength and environment temperature are given.
In this paper, a method for measuring long microwave optical fiber delay line is presented, which can resolve phase ambiguity, filter leakage signal, and reduce noise effect. An example is given by measuring an 8.6 km externally modulated optical fiber delay line. The measured results demonstrated the efficiency of the measurement method.
A kind of connector utilizing self focusing optical fibers is designed to couple Lambertian point source to multimode optical fibers. According to the emission pattern of the source and transmission characteristic of self focusing optical fiber, our calculation result shows that such a coupling scheme can improve coupling efficiency and tolerance.