The effect of the multi-region crack growth model on the fiber lifetime prediction in the optical communication systems and the problems to be solved before putting the new model into practice are discussed.
Standard glass optical fiber was intentionally damaged and strength tested in tension for a wide range of failure stress values. The mirror/mist boundary on each specimen was measured and compared to the measured failure stress. When the size of the fracture mirror is small compared to the fiber diameter, the well-known linear square root dependence of strength on mirror size was reaffirmed. However, when the mirror size approaches the fiber diameter, this relationship does not hold. The classical relationship overestimates the failure stress for large mirrors. It was determined that the circular shape of the fiber contributes to, but can not fully account for, departure from the classical strength/mirror relationship. A new empirical relationship was developed to enable predictive determinations of failure stress to levels as low as 20 to 25 kpsi (0.14 to 0.17 GPa).
A technique was developed for obtaining proof-stress level flaws in commercial optical fiber with low variability in strength. It involves a novel method for stabilizing and protecting the round fiber prior to indentation. Indentation was performed in an automated fashion using a nano-indenter equipped with a cube-corner indenter. A Weibull modulus of 50 was achieved with a value of 100 over the lower portion of the distribution. This method will be useful in static fatigue testing of fiber with proof test level flaws.
Single mode and multimode tellurite fibres were drawn from preforms of TZN composition (75TeO2 20ZnO 5Na2O) to which 2 mol-% of BaO or La2O3 had been added in the cladding, and their mechanical properties determined. Average bending strengths of 540 to 830 MPa were found after determination of the Young's modulus, which amounted to 46.3 GPa and 46.1 GPa for TZNB and TZNL, respectively. Compared to fluorozirconate fibres drawn previously under nearly the same conditions, average bending strength increased by more than 30 %. On aging in water, the strength of tellurite fibres with TZNL cladding remained unchanged even after 10 days. That of fluoride decreased by more than 50 % within 24 h. Fractographic analysis on fractured tellurite fibres yielded a mirror constant, M, of 1.017 MPa.m1/2. No difference was seen between aged and pristine fibres. By contrast, the mirror constant of fluoride fibre decreased by 10 % on aging. Vickers indentation on TZNL clad glass resulted in a Vickers microhardness, HV, of 3.18 GPa and a fracture toughness, KC, of 0.25 MPa.m1/2. Based on KC and glass structure, an attempt was made to relate fractographic results to the fractal geometry concept as proposed by Mecholsky.
Based on the microbend characteristics of the multimode optical fiber (MMF), a novel twisted fiber torsion angle sensor is demonstrated firstly. The experimental principle and the basic formula have been analyzed and given. The experiment shows that the microbend loss of the multimode optical fiber is sensitive to the torsion angle. In the range of torsion angle from 0 degree(s) to 90 degree(s) the sensitivity is about 1dB/degree. The experimental results are well agreement with the theoretical ones.
A novel method for incorporating static fatigue results into dynamic fatigue curves allows one to significantly extend the range of experimental fatigue results for further analysis. One obtains a power-law description of static fatigue data over a narrow range of time-to-failure and subsequently translates the data into this region into dynamic fatigue data. This recalculation method applies to data that does not follow the traditional power law model.
In this paper we define what we consider the current defacto paradigm for accelerated testing, discuss what is wrong with it, introduce a more rigorous paradigm, and develop some theory for the new paradigm. Examples used for illustration include modeling degradation of connectors under cyclic stress, modeling degradation of metal films, and a pure Arrhenious thermal model of failure.
The mechanical reliability of fused silica glass fibers is significantly influenced by the properties of their polymer coatings. The primary coating, which is in contact with the fiber surface, is expected to control the chemistry there, but the secondary coating does have a considerable effect on the strength and aging behavior of the fiber. This observation is confirmed by data obtained for ten fused silica fibers, having the same primary coatings but ten different secondary coatings. These fibers were aged at 85 degree(s)C in both de-ionized water and 85% relative humidity for up to 6 weeks and the residual strength as a function of aging time was measured. Dynamic fatigue measurements were carried out on as-received and aged fibers using two-point bending. The results show that the secondary coating has a notable effect on the aging behavior and the coating strip force, but does not greatly influence the dynamic fatigue parameter.
The mechanical performance of two optical fibers samples (Sample A and Sample B), each from a different fiber manufacturer and colored by the same ultraviolet (UV) coloring process, was compared with that of a third sample, referred to as reference fiber. The mechanical performance was evaluated by fracture stress, strip force and pullout force and was correlated with the physical- chemical properties of the fiber coatings, as revealed by Fourier Transform Infrared Spectroscopy (FTIR) and Dynamic Mechanical Thermal Analysis (DMTA). The comparison of the three fibers revealed that fracture stress, strip force and pullout force were higher for the reference fiber than for the fibers of Sample A and B. Explanation for these observations were given in terms of the rubber and vitreous states of the fiber coatings, as well as the presence of additional phases in the coatings. It was also found that the mechanical performance of the fibers of Sample A and Sample B changed with the UV coloring process. These changes were observed to be different for each sample, as a result of the differences in internal coating structure. However, regardless of the changes, the mechanical performance of Sample A and B was always inferior to that of the reference fiber.
Fiber used in an undersea cable encounters different stresses from fiber manufacture to final cable manufacture. Usually fiber experiences the highest stress at its required prooftest during fiber manufacture. For the processes of an undersea cable, fiber usually experiences much less stresses. However, one of the cabling processes was identified to have higher stress than expected, which is the insulation jacket extrusion of a deep-water cable. This paper models the fiber strain in this process and proves its consistency with observed data. The cause of higher fiber strain is believed to be from thermal expansion of the filling compound gel in the loose tube portion of the cable. This change of gel is modeled to demonstrate that the fibers are affected locally and are stretched simultaneously with gel movement. This phenomenon is temporary and the fiber strain changes with the gel temperature during the manufacturing process.
Industrial applications of polymer optical fibers (POF) require a high reliability of the optical data transmission. Therefore it is necessary to investigate the behavior of POF under extreme environmental stressing. For these investigations specific measuring equipment is necessary. The design and practical applications of a multiplexer for optical transmission measurements and of a high-resolution OTDR for damage analysis are described.
A novel method for measuring the temperature-dependent chromatic dispersion of a fiber is proposed, which is based on the interference fringe formed by a pair of long-period fiber gratings (LPGs). The effective index difference between the fundamental core mode and a cladding mode was obtained from the interference fringe of the LPG pair. The order of the involved cladding mode and the core size could be obtained from the general parameters of the fiber; the numerical aperture and the cut-off wavelength. Using the obtained cladding mode order and the Sellmeier equation of silica material for the cladding index, the refractive index of the fiber core was obtained by comparing the measured effective index difference with the calculated one. Since the temperature-dependent Sellmeier equation of the cladding material is already known, the temperature-dependent refractive index of the core can be obtained. Measured refractive index of the core is fitted with a linear combination of the well-known Sellmeier equations of germanium and silica. The concentration of germanium is used as the fitting parameter. The calculated chromatic dispersion is well matched with the one measured with a conventional instrument within 0.2 ps/km/nm in a spectral range of from 1.3 mm to 1.6 mm at room temperature.
In this report we analyze experimental data on the degradation of connectors that are undergoing temperature humidity cycling. The data produced to date give a strong indication that connector degradation under the high stress conditions used to date is consistent with a mechanism driven by multiple distributions of flaws in the epoxy bonds. The current model and statistical evidence are discussed, and related to some theoretical work done previously. In addition, some suggestions for further experiments are made to explore the acceleration dynamics of the mechanism.
Estimating the reliability of new products is an important part of new product development. There are several ways in which this reliability can be estimated, including the use of: field data, empirical reliability prediction models, test data, and reliability physics based models. Field data is usually the most desirable for estimating the reliability of a product since it represents the deployment conditions and therefore represents all applicable stresses to which the item is exposed. There is typically not enough operational field data to estimate the reliability of products in a statistically robust manner, and therefore using field data alone leads to low statistical confidence inferences on the measure of failure rates. This paper presents a practical and structured approach to estimating the reliability of components used in photonic systems. This approach consists of a generic model that allows for the fusion of various data types (e.g., tests, models, simulations), and merges available data with a Bayesian approach to form the best estimate of component reliability. This paper explains the theoretical robustness of the method, and demonstrates the Bayesian method. The approach is particularly suitable for photonic components given the short development times typical in the telecommunications industry and the resulting relative scarcity of field data.
Varying the intensity of illumination used to cure photoactivated adhesives has been applied in medical and dental applications to improve the performance of polymer materials. For example, it has been observed that dental polymer composite materials express reduced shrinkage, important for durability of non-amalgam restorations, by introducing a phased time-intensity cure schedule. This work identified that curing conditions could influence the final properties of materials, and suggested the possibility of extending the characteristics that could be influenced beyond shrinkage to humidity resistance, Tg, outgassing and other important material properties. Obviously, these results have important ramifications for the photonic industry, with current efforts focused on improved manufacturing techniques. Improvement in low cost packaging solutions, including adhesives, will have to be made to bring the component cost down to address the needs of Metro and similar markets. However, there are perceived problems with the widespread use of adhesives, the most prevalent of these involving long term durability of the bond. Devices are typically aligned to sub-micron precision using active feedback and then must be locked in position to maintain performance. In contrast to traditional fastening methods, adhesive bonding is a highly attractive option due to the ease of deployment, lower equipment costs, and improved flexibility. Moreover, using methods analogous to those employed in dental applications, materials properties of photonic adhesives may be tailored using a programmed cure approach.
A study is made into the effect of stripping the polyimide coating by hot acid immersion on the tensile fracture stress of polyimide- coated optical fibre. It is shown that the strength does not degrade for one or multiple lengths of stripped fibre, nor for long (lengths up to 150 mm) stripped areas. Recoating with polyimide is performed and it is shown that, although strength degradation can occur due to the increased handling, it does not necessarily do so. Strength distributions of pristine, chemically-stripped, laser- ablated and recoated fibres indicate the magnitude of flaws introduced by handling, which are likely to be the cause of strength degradation.
Coatings on optical sensors provide protection from mechanical damage and chemical attack. In high pressure, high temperature environments, conventional polymer coatings allow hydrogen and moisture to diffuse into the fiber core, causing failure in sensors that operate in harsh environments. A hermetic carbon coating can be used in these applications to improve reliability in sensing and signal transmission, and to extend fiber life. An experimental study of thin carbon films applied by chemical vapor deposition (CVD) was conducted to determine the effects of deposition parameters on film hermeticity. The goal is to control carbon disposition in a cold walled CVD reactor by controlling the gas flow, temperature, and concentration of reaction gases within the chamber. The experiments grow carbon films by CVD of hydrocarbon precursors on stationary quartz glass rods. Smooth, pinhole free graphite films have been obtained and are desired because they prevent the diffusion of hydrogen. The carbon layers are analyzed for thickness, carbon phase, and surface roughness using ESEM and Raman Spectroscopy. The information will be combined with a numerical study to optimize the growth of graphite films on optical fibers.
Acoustic vibrations on standard SMF fiber generates long period grating inside optical fiber that can be used for various filtering applications. Tunable acousto-optic filters are currently used in dynamically controllable optical signal processors. The combination of acoustic and optical technologies presents some interesting reliability perspectives. This paper uses the framework of the development of an acousto-optic tunable filter to 1) demonstrate the wisdom and strength of design for reliability and 2) illustrate a robust approach to achieving qualification compliance in one design cycle for a product that uses technologies that are not mainstream to the telecom optical industry.
The strength of standard silica fibers has been measured in wet and hot atmosphere. Static fatigue measurements have been carried out at temperatures ranging from 20 degree(s)C to 70 degree(s)C and relative humidity RH varying between 40 and 80 %. They were wound around alumina mandrels to apply a permanent stress lying between 2.7 and 3.5 GPa.. The evolution of the failure times with respect to temperature, applied stress and RH has been studied, leading to a general relation including. Arrhenian semi empirical constants. This relation is similar to that found for fibers immersed in liquid water. Our results are consistent with precious works. This empirical expression could be derived theoreticaly using the vacancy model of the vitreous state.