The effect of ions in solution on the stress assisted mechanical corrosion of high strength lightguide fibers is compared to the rate of crack growth in bulk silica. This review shows that the mechanical corrosion of bulk silica is apparently insensitive to ions in solution, whereas, fatigue of uncoated lightguide fiber is ion sensitive. These observations are discussed with respect to long term mechanical reliability.

Optical glass fibers can exhibit, under severe environmental conditions, an accelerated static fatigue behavior at long times under moderate stresses. This behavior is manifested by a transition, or 'knee', in the plot of ln (time to failure) versus ln (applied stress). This accelerated fatigue effect depends on several variables, including temperature, relative humidity, and pH, as well as on the composition of the cladding and polymeric coating. Similarly, optical fibers can exhibit a pronounced strength degradation due to zero stress aging. It was found that the onset of significant strength loss during zero stress aging occurred at about the same time as the static fatigue transition. Also, the spread in the distributions of time to failure at a given applied stress narrows after the transition. These results suggest that zero stress aging represents a second mechanism of crack growth which takes place on a longer time scale and is superimposed on the crack growth of stress corrosion. Finally, a model was used to predict this accelerated fatigue behavior in optical glass fibers by assuming the combined influence of zero stress aging and stress corrosion on crack growth.

It is found that by abrading an optical fiber surface, a controlled strength distribution can be produced that is effective for dynamic fatigue testing of large flaws. Dynamic fatigue testing of 30 kpsi flaws overcoated with carbon yielded n values greater than 100. It is believed that the abraded fiber samples can be utilized as a surrogate for measuring the fatigue parameters of carbon coated splices and flaws near the proof test level. In addition, it was found that overcoating abraded fiber with carbon increased the strength by a factor of two. This increase is more than what would be predicted by the increase in fatigue resistance that comes with carbon overcoating, and suggests deposition of carbon alters the flaw geometry or stress field surrounding the flaw.

The x-ray imaging technique has been successfully applied to nondestructive evaluation of failed optical fiber splices. This technique can detect fiber fractures and defects inside mechanical and fusion splice samples. It is particularly effective in analyzing field failures since it requires no sample preparation and offers the advantage of preserving sample integrity. The x-ray imaging technique provides magnified real-time or film images of optical fiber inside splices with high resolution. In addition, the image processing capability provides image enhancement which significantly improves the clarity of the images. In examining samples of fusion and mechanical splices, we identified fiber fracture and separation of fiber ends as the most common failure mechanisms of splices. Fiber fracture was the result of fatigue failure when the stripped fiber section was subjected to severe abrasion damage and excessive stress. Subsequent fractographic analysis of fractured fiber ends supported the finding from x-ray imaging. Therefore, the x-ray imaging technique has proven to be a powerful tool for analyzing failed splice samples and it is a valuable addition to conventional analytical techniques.

Optical fiber coatings play an important role in strength, fatigue and attenuation performances. The strength and fatigue properties are particularly sensitive to temperature and environment. Optical fibers were coated with polymeric coatings such as ultraviolet (UV) cured acrylate and polyimide, and hermetic coatings such as amorphous carbon. Their strength and fatigue properties at different temperatures were studied.

Recent advances in the understanding of reliability of silica optical fiber indicate that the chemical durability of the fiber can control the long duration lifetime both under stress- induced fatigue and zero-stress aging conditions. In particular, dissolution of surface material produces strength degrading surface roughness. These mechanisms are discussed and strategies for improving reliability by inhibiting dissolution are examined. As an example, a modified polymer coating formulation is described that is shown to increase the lifetime of the fiber by up to a factor of thirty-fold. Strategies for improving the strength and durability of non-oxide fibers using a similar approach are also discussed.

Optical fiber used in telecommunication networks encounters environments ranging from essentially dry to very high relative humidity. Mechanical properties of optical fibers must be maintained in these different environments. The mechanical properties of a number of UV cured inner and outer primary optical fiber coatings were examined as a function of relative humidity. It was observed that the mechanical property changes as a function of relative humidity were related to the water sensitivity of these coatings. Coatings with higher peak water absorption showed a larger decrease in mechanical properties.

Three commercially available telecommunications fibers were aged under zero mechanical stress in 85 degree(s)C and 30 degree(s)C water and in two hot, humid environments, 85 degree(s)C at 85% r.h. and 85 degree(s)C at 60% r.h. The strength of the fiber, as well as the stability of its protective polymeric coating, have been monitored periodically for aging times of up to 1 year in these environments. The fiber strength and coating integrity must be maintained in order for fibers to be handled safely during routine termination procedures in the outside plant.

During the fabrication and field installation of fiber optic cables, a combination of torsion and tension may result in premature failure of optical fibers. In this paper, we examine changes to the fracture stress of fibers due to externally applied tension and torsion by analyzing the fiber end faces. Analysis of the fiber fracture surface indicates significant deviations from the typical tensile pattern in both the glass surface and the protective coating.

One-third of the proof-test stress has been commonly quoted as the maximum allowable stress to ensure longevity of fibers. However, the basis of the rule are not appropriate for some installation practices and modern fibers. The Weibull parameter m for low-stress breaks was measured using a proof tester. The fatigue constant n was replaced with the parameter obtained from an abraded fiber. Using the new parameters and appropriate failure probabilities, engineering guidelines were derived for three representative lengths: 1000 km (long-haul cable), 1 m (fiber in a splice closure), and 1 cm (bent section of a pigtail fiber).

A demonstration of the ability of an existing optical fiber cable to survive the harsh environment of a rocket engine was performed at the NASA Lewis Research Center. The intent of this demonstration was to prove the feasibility of applying fiber optic technology to rocket engine instrumentation systems. Extreme thermal transient tests were achieved by wrapping a high temperature optical fiber, which was cablized for mechanical robustness, around the combustion chamber outside wall of a 1500 lb Hydrogen-Oxygen rocket engine. Additionally, the fiber was wrapped around coolant inlet pipes which were subject to near liquid hydrogen temperatures. Light from an LED was sent through the multimode fiber, and output power was monitored as a function of time while the engine was fired. The fiber showed no mechanical damage after 419 firings during which it was subject to transients from 30 K to 350 K, and total exposure time to near liquid hydrogen temperatures in excess of 990 seconds. These extreme temperatures did cause attenuation greater than 3 dB, but the signal was fully recovered at room temperature. This experiment demonstrates that commercially available optical fiber cables can survive the environment seen by a typical rocket engine instrumentation system, and disclose a temperature-dependent attenuation observed during exposure to near liquid hydrogen temperatures.

A rotating capstan fiber tester (RCFT) differs from an Instron-type translating test device primarily in the method of strain. That is, even with a constant capstan rotation rate, an RCFT does not strain fiber at a uniform (constant) rate. In this paper exact relationships for RCFT strain and strain rate are derived. Strain is an exponential function of rotation and strain rate is a function of instantaneous strain. It is shown however that the difference between a rate assumed constant and an exact, strain dependent strain rate is negligible with respect to resulting break strengths. Preliminary comparison testing demonstrates that the mean strength values between instruments are, within measurement variability, different by no more than predicted levels of a fraction of a percent.

A plating process was developed to deposit Ni-P, nickel and gold on an optical glass fiber. The tensile strength of the metallized pigtail increases when the oxidation time, or the electrolytic Ni or Au layer thickness increases, or when the electroless Ni layer thickness decreases. A pull force of more than 1,000 g is routinely obtained on soldered metallized optical fibers. Optical fibers retain their hermeticity after plating and soldering. Soldered metallized optical fibers have a lifetime expectancy over 20 years even when submitted to continuous stresses above 100 MPa.

New approaches to improve the prediction of failure of long length fibers are presented. They are currently being used in type approval and quality control of optical fibers and cables in Swedish Telecom. One approach is to use the B-parameter. Values on this parameter, usually obtained from testing in liquid nitrogen, high temperature, or under vacuum, are not being considered very useful for lifetime estimation in regular environments. Therefore, a high- speed tensile test has been developed, by which the B-parameter is evaluated, at adequate service conditions. The other approach, to long-term fatigue data, is the expander test by which static and dynamic tests are made on medium length fibers under uniaxial stress. Long- term failure statistics are conveniently accessed by testing a single specimen. Limitations of the techniques are discussed: influence on fatigue parameters of static versus dynamic load and testing environment, and fatigue of high strength versus low strength modes.

We have developed a magnetron sputter coating method to continuously coat silica optical fibers with a dual layer coating of Inconel 625 alloy and platinum. The coating process is performed on-line as the fiber is drawn to minimize the rapid strength degradation of the silica due to attack by moisture in the air. Because of the modular design of the sputter equipment, the process is well suited for the deposition of a wide variety of metals and is readily adapted for scale-up. Multimode optical fibers were produced with coatings up to 0.5 microns in thickness consisting of an adhesion layer of Inconel and an outer layer of platinum. The coatings are adherent and remain mechanically intact after thermal cycling between room temperature and 2000 degree(s)F in vacuum. Approximate tensile strengths of 145 to 290 Kpse have been measured. These attributes make this sputter coated fiber a promising candidate for use in high temperature environments.

The need for suitable remote sensors in highly radioactive defense waste storage tanks is discussed. The harsh radiological and chemical tank environment precludes the use of standard sensors because of the need for intrinsically safe systems. Potential sensor systems based on fiber-optics technologies suitable for hardening to the tank environment are identified. The need for certification standards for this type of environment is also discussed.

Dielectric optical waveguides exhibit properties that are well suited to sensor applications. They have low refractive index and are transparent to a wide range of wavelengths. They can react with the surrounding environment in a variety of controllable ways. In certain sensor applications, it is advantageous to integrate the dielectric waveguide on a semiconductor substrate with active devices. In this work, we demonstrate a tamper sensor based on dielectric waveguides that connect epitaxial GaAs-GaAlAs sources and detectors. The tamper sensing function is realized by attaching particles of absorbing material with high refractive index to the surface of the waveguides. These absorbers are then attached to a lid or cover, as in an integrated circuit package or multi-chip module. The absorbers attenuate the light in the waveguides as a function of absorber interaction. The absorbers are placed randomly on the waveguides, to form a unique attenuation pattern that is registered by the relative signal levels on the photodetectors. When the lid is moved, the pattern of absorbers changes, altering the photodetector signals. This dielectric waveguide arrangement is applicable to a variety of sensor functions, and can make use of resonant coupling properties between low refractive index dielectric waveguides and high-index absorbing materials.

In order to estimate the radiation sensitivity of a data transmission system based on optical fibers, the radiation-induced loss of other included passive components has to be known, too. We have irradiated (at room temperature) a variety of couplers made by different manufacturers at a ⁶⁰Co source with a dose rate of 1300 rad(SiO₂)/min up to a total dose of 10⁶ rad(SiO_2$. Most of them were fabricated by the Fused Biconical Taper process of 200/280 micrometers multimode step index fibers (tested at (lambda) equals 850 nm), and of 10/125 micrometers single mode fibers (tested at (lambda) equals 1300 nm and (lambda) equals 1550 nm). Couplers with 50/125 micrometers gradient index fibers (tested at (lambda) equals 850 nm and (lambda) equals 1300 nm) were also among them. The measured coupler inherent losses were between about 0.01 dB (fused coupler, high OH MM step index fibers, (lambda) equals 865 nm) and about 50 dB (coupler made of GRIN lenses, (lambda) equals 865 nm).

More than 10 existing lifetime models for optical fibers, based on a power law to describe the stress-induced crack growth, are studied and compared. The number of models is reduced to only 1 basic model. This model is taking into account the effects of proof test. An alternative model, to be used when proof testing is performed on-line, is given as a worst-case limit of the basic model. A choice of 3 testing methods to obtain information about the weak-flaw distribution is given: dynamic-fatigue and variable screen-testing of long lengths or using the failure number during proof test. The models can also be used for titanium-doped fibers, but then a correction must be made for the compressive surface-stress. The lifetime models cannot be used for carbon-coated fibers and for fibers in water without further study.

Telecommunication systems currently being considered for deployment will use large numbers of Wavelength Division Multiplexers/Demultiplexers (WDMs) and uniform or nonuniform couplers (or splitters) in the outside plant. These passive fiber optic (PFO) components will be installed in pedestals, be deployed in aerial cables and be buried underground; and they will be expected to exceed the high reliability and low maintenance of the copper they replace. In order to demonstrate the long-term capability of the PFO components to perform their function reliably, they must pass a comprehensive reliability test program which attempts to duplicate the stresses which the components are expected to experience over a 20 year operating life. The qualification test requirements for PFO components are addressed in Belicore Technical Advisory TA-NWT-001221 "Generic Requirements for Passive Fiber Optic Component Reliability Assurance Practices" 1 PFOcomponents are currently being produced by several technologies, i. e. ,fused biconic taper, integrated waveguiding substrate, or GRIN-rod lens. The generic requirements in TA-NWT-001221 are based on application requirements and were developed without regard for a particular manufacturing technology. Bellcore has undertaken a program to support these generic requirements by subjecting PFO components from several manufacturers to accelerated stress tests. The tests are based on industry accepted standard test procedures (principally EIA/TIA), and the test conditions are based on the environments the components are expected to encounter in the field. The requirements of the proposed qualification test program, the tests being performed in support of these generic requirements and the results obtained to date, are the subject of this paper.

The experience is presented with respect to development of testing methods as well as optical fiber and cables of home-made and foreign origins test results. The analysis of accumulated statistics became the basis for prediction of service term of fiber-optics systems under given operational conditions and for non-destructive hidden defects diagnostics technique of optical fiber and cables.

We report energy-dependent proton and Co-60 test results and analysis assessing performance of In_0.53Ga_0.47As photodetectors and In_0.71Ga_0.29As_0.61P_0.39 laser diodes for satellite applications. Calculations of the nonionizing energy loss (NIEL) for protons in InGaAs allow damage assessment using a general technique for evaluating displacement damage in orbit. Device performance is predicted for several shield thicknesses and orbital conditions. We also discuss effects in optoelectronic devices due to total dose and ionization transients.

Two classes of quantum-well-based fiber-optic light sources are examined for degradation under 5.5-MeV proton irradiation as part of an evaluation study for satellite applications. Contrary to previous experience with bulk active area heterostructure light-emitting diodes and laser diodes, it was found that these quantum-well light-emitting diodes are more tolerant of proton irradiation than quantum-well-based lasers. This is the case when the quantum-well light-emitting diode structure allows operation far into gain saturation and the cavity is lossy compared with the quantum-well lasers where gain is more sensitive to current density and with low-loss cavities. Experimental damage factors were measured for performance parameters of these quantum-well photonic devices and found to be similar to those previously reported for carrier removal rates in GaAs-based electronic structures.

Arrangements of discrete photonic waveguide devices are currently being integrated to form circuits. These Photonic Integrated Circuits (PICs) require test methods that are adaptable as circuit size and complexity grows. Here, we describe tests used to characterize a GaAs/GaAlAs waveguide-based PIC being developed for phase-shift control in phased-array antenna applications. The various elements of the PIC include digital and analog waveguide modulators, light-guide splitters and combiners, turning mirrors, and input-output polarization-maintaining single-mode optical fibers. These basic elements are combined to perform higher-order functions such as optical frequency translation (single side-band suppressed carrier modulation), and phase shifting on multiple optical taps. Tests used to characterize the elements include optical loss, guided-wave modal characteristic, antireflection coating effectiveness, electro-optical (phase) modulation efficiency, electrical frequency response, and optical frequency translation. These tests are integrated with the fiber attachment and RF packaging sequence to construct working device prototypes. They are currently being applied to discrete components of the circuit, and will be adapted as the various parts are integrated.

With the increasing use of optical data links it becomes essential to test for radiation vulnerability not only the transmission support--fiber and cable--but also fiber-end electro- optical components that could be exposed to hostile environment. Numerous silica-based fibers were currently tested over the world. This paper gives a comparison of radiation resistance between two gradient index multimode fibers with and without phosphor in core. From that result a technological change in standard 1.3 micrometers wavelength light-emitting diodes (LEDs), injection-laser diodes (LDs) and p-i-n photodiodes (PDs) was made. Results of tests under steady-state medium dose-rate Co⁶⁰ exposure show a significant enhancement of improved components optical performance. Especially LED and PD present a small degradation of optical characteristics for 50 kGy (for a dose-rate of about a few 10 Gy h^-1). Multicomponent laser-diode modules (LDM) were extensively tested up to about 20 kGy. Two degradation processes clearly appear: a wrong decrease of stimulated light emission after 3 - 4 kGy and a bad operation of thermoelectric element cooler beyond about 10 kGy. Hardened optical data links are now able to withstand successfully some nuclear environments.

Experiments to determine the effects of exposure to ionizing radiation and hydrogen on erbium fibers and erbium fiber amplifiers are described. A preliminary assignment of the radiation induced losses to components of the fiber composition is made. Both reversible and long term losses resulting from hydrogen permeation have been observed. As in other types of fibers, the presence of hydrogen modifies the response to radiation.

High purity, high-OH, silica optical fibers were irradiated in a hydrogen atmosphere to explore hydrogen binding into defects created by the ionizing radiation. Significant improvements in subsequent measurements of steady state radiation-induced attenuation were observed. Transient and steady state radiation-induced attenuations and long term stability of the phenomena were evaluated.

Optical fibers with undoped silica core and fluorine doped silica cladding are known to be radiation resistant. Especially fibers with high OH-content core material show very low radiation induced losses which recover within a few hundred seconds after irradiations up to 100 krd dose. Even with these promising properties radiation resistance is a limiting factor for some applications. Optical fibers with different grades of high OH-content undoped silica core materials were produced by using the same preform manufacturing and fiber drawing parameters. The UV-attenuation spectra of those fiber samples were measured. Then they were irradiated at a ⁶⁰-Co-source, and the induced losses were recorded in the spectral range between 200 nm and 1600 nm wavelength. A correlation between the UV-attenuation characteristics of the unirradiated fiber and its radiation induced loss was found. The results indicate that defects already existing in the unirradiated fiber ('precursor defects') are responsible for the differences in radiation resistance at dose values below 100 krd. These precursor defects are transformed into color centers by ionizing radiation.

The radiation-induced loss of multimode step-index fibers with undoped synthetic silica core has been reduced significantly over the years. Most of the efforts focussed on material modifications and improvements of the undoped core material having either high or low OH- content. With increasing radiation resistance due to core material improvements, influences of the core-cladding interface and of the cladding material became more important. These effects can be analyzed with an improved measurement system using different excitation conditions at the frontface of the step-index fibers: low order meridional rays have high intensity in the center of the core material and low intensity in the core-cladding transition region, in contrast to high order skew or helix rays having opposite intensity profiles. The measurement system including the specific excitation conditions is described. Applying this setup, radiation-induced losses during and after continuous gamma irradiation were investigated with regard to differences of the specific excitation conditions. The measured values at 10 krad total dose differ by more than a factor of two.

We have measured the effects of radiation on various optical LAN communication components. The measurements were performed with 2.5 MeV electrons from the Lehigh University Van de Graaff. The performance of the devices was monitored both during irradiation and after irradiation.

Polarization-maintaining fibers were irradiated with 1.5 ns electron pulses. Linearly polarized light was injected into the fiber, aligned either parallel or perpendicular to the fiber core's stress axis. Linearly polarized light was detected with a high speed optical system, with polarization axis either parallel or perpendicular to the stress axis. Light throughput and attenuation were documented in these four geometries. No differences were observed in radiation-induced attenuation between the two injection conditions when the output observations were aligned with input orientation. No evidence in this time regime was seen for radiation-induced mode crossover, i.e., no signal (to < 1% of the power transmitted along the injection axis) was observed in the cross polarization state at the output as a consequence of the irradiation.

Polarization maintaining fibers hardened against fission neutron irradiation will be an essential element to future DoD and DoE applications which will include optical processing systems, inertial measurement devices, and sensors. This paper reports on the effects of prompt neutron fluence on the orthogonal components of an optical signal transmitted through a polarization maintaining fiber.

The survivability of optical fibers for data bus and gyroscope applications in the natural space radiation environment has been analyzed using radiation-induced loss data of single mode, multimode, and polarization-maintaining fibers. Since it is virtually impossible to simulate the dynamic conditions of space, extrapolations have been made from measurements at dose rates, temperatures, and total doses different from those onboard spacecraft. The anticipated degradation of most Ge-doped silica core fibers and all pure silica core fibers appears to be well within allowable margins in fibers for data bus applications, while the radiation sensitivity of polarization-maintaining fibers could result in a significant decrease in fiber gyro performance.

Optical fibers are currently under consideration for use in spacecraft systems as an essential component of fiber optic gyroscopes and rotation sensors. The fibers which are utilized in fiber gyros and sensors are polarization maintaining. Many of these spacecraft systems will encounter radiation levels reaching the 75 kilorad level over the mission life. In addition, temperatures may range from -30 to +65 degrees Centigrade during the spacecraft's operation. This paper investigates the radiation effects on a new type of polarization maintaining fiber over the operational temperature range and up to a total dose of 75 kilorads. Comparisons are made between previous fiber test results and the Andrew ECore fiber test results. Results indicate that fiber gyros utilizing the ECore fiber will survive the long term radiation environment in space.

The radiation-induced coloring of erbium-doped optical fibers (EDF's) is reported. The radiation hardness of the EDF's is observed to be strongly dependent on composition. The implications for erbium-doped fiber amplifier (EDFA) performance is modelled.

Fiber optic connectors and splices have been in service for over a decade and now number in the tens of millions. Although the reliability level ascertained from Performance is quite good, there are presently no well defined testing and analytical methods in place for predicting reliability. This is due in large part to the variety of potential failure modes and service environments. As fiber expands in the telecommunications network and into other applications such as private LANs, data links, and control systems, the need for reliability prediction methodologies has become increasingly important. This paper addresses the issues related to this problem.