Emerging services will need extensive fiber optic systems in interoffice and loop applications. New systems are being designed to meet these needs. Advances in technologies enable very high speed (several gigibits/second) transport systems in interoffice applications and in loop applications. Tins paper will overview fiber system failure data from field analysis, discuss two new reliability considerations, and highlight new reliability challenges facing Fiber-In-The-Loop (FITL).

Following a brief review of the radiation environment encountered by NASA spacecraft, we present examples of the use of fiber optic and optoelectronic components in this environment. Initial results of the fiber optic experiments on the recently retrieved Long Duration Exposure Facility (LDEF) will be presented. Very little radiation induced attenuation was observed during the LDEF flight. Next, we discuss the application of a Fiber Optic Rotation Sensor (FORS) on the JPL CRAF/Cassini missions. For these relatively long missions, reliability is expected to be more of an issue than radiation damage. Finally, we briefly discuss the application of fiber optic data busses to NASA spacecraft. Because of the short fiber lengths required, radiation is not expected to be a serious problem with data link applications.

This paper examines several possible deployment variations in near-term Fiber-In-The-Loop (FITL) network architecture from a reliability perspective. The reliability impact of network topology is modeled and compared to current Bellcore availability objectives. The study indicates that careful consideration of network architecture before deployment can minimize service unavailability. However, aggressive efforts to improve equipment/media reliability are crucial in achieving the availability objectives; these efforts should be focused on the distribution segment of FITL architecture, which is estimated to produce the largest contribution to overall downtime. Results also indicate that present availability objectives for various network elements need to be re-allocated under FITL to reflect more accurately the relative reliability of FITL hardware and media.

The optical time domain reflectometer is a powerful diagnostic tool for use on optical networks. However, high spatial resolution can only be obtained at the expense of dynamic range, limiting its effectiveness when applied to high-loss fibre routes. High-gain, wide-bandwidth erbium-doped fibre amplifiers can be used to increase the peak pulse power of narrow OTDR pulses at 1550nm to 2W. An increase of 8dB in dynamic range can be realised whilst maintaining spatial resolution.

As the fiber-optic revolution moves from the long-haul telco environment into the pedestal environment, mechanical performance requirements on optical fiber will be more rigorous. This will require fiber and fiber coatings which can withstand a wider variety of environments and possess improved handling properties. Corning Titan™ SMF CPC5 fiber was specifically designed to meet such new demands on the mechanical performance of optical fibers. The performance improvement was realized through modifying the silica glass surface with titania, along with the use of a new acrylate coating. This paper reports the experimental results of testing the strip force, coating abrasion resistance, strength, and dynamic fatigue before and after prolonged exposure to salt water, acidic and basic solutions, hot-dry environment and temperature-humidity cycling.

In any communication system, and particularly for a telecommunication system, the transmission medium is required to be highly reliable. Prior to 1980, most of the telecommunication networks deployed copper cables.

Optical fiber coatings play an important role in fiber strength, fatigue and attenuation at different temperatures. The major function of the coating is to protect the glass surface from external abrasion and environment, and to preserve strength. Polymeric coatings such as ultraviolet cured epoxy acrylates, silicones, and polyimides are commonly used. The use of polyimide coating on optical fiber has become increasingly important for high temperature applications. The strength and fatigue properties of optical fibers with polyimide coating were studied at different temperatures.

The strength and fatigue behavior of bulk fused silica is well understood in terms of the growth of microcracks under the combined influence of stress and environmental attack. The behavior of high strength, flaw free silica optical fiber shows significant differences from the bulk material for poorly understood reasons making long term predictions unreliable. It is known that silica fiber strength and fatigue are sensitive to such environmental parameters as temperature, humidity and pH. However, this paper presents results which also show a sensitivity to ionic species in the environment. These results are interpreted in terms of possible models for the fiber behavior.

High reliability and low maintenance are critically important attributes of optical cable. Considering the service environment, we can predict some of the possible failure modes of optical cables and develop testing programs for them. However, it is unrealistic to expect that all modes of failure can be anticipated and understood quantitatively. Sometimes the cause of the failure is obvious but other times the cause of the failure is poorly understood and is worthy of further investigation. By conducting over 30 post-mortem analyses, we have gained an improved understanding of potential failure modes.

This paper reports the results of temperature cycling and thermal shock tests on commercially available laser modules designed for uncontrolled environments. Components in these installations must withstand a much wider temperature range than that of a telephone central office. The lasers tested in our experiment include receptacle packages, cylindrical packages with pigtails and rectangular packages with pigtails. We have observed some anomalous characteristics such as unstable spectra, non-linear L-I (power versus current), and non-constant front-to-rear tracking ratio. The appearance of these anomalies challenges our ability to economically screen those problem devices.

Electroluminescence imaging along the optical channel of a laser diode can show non-radiative defects or non-uniform emission in the channel which may be contributing to failure. This imaging technique is easily done on specially prepared test sites or on lasers that have not been diced and packaged. Once the laser diode is packaged (typically in a TO type package) it is difficult to utilize this technique due to the difficulty in successfully exposing the optical channel for inspection. This paper describes a practical technique to perform optical channel electroluminescence imaging of packaged laser diodes. It has been successfully applied to 780nm, 800nm, and 1300nm laser diodes. The information obtained can be used to improve reliability and/or life of the product analyzed. This paper will highlight details of the technique along with illustrations of typical results. Applications to failure analysis will also be discussed.

The strength of the long lengths of fiber contained in optical cables is determined by the presence of the few large flaws that are produced infrequently by normal fiber production methods. To investigate the behavior of low strength fiber containing these critical flaws, we have produced a fiber containing many large flaws by passing an as-drawn, uncoated fiber over a wheel coated with abrasive. The effect of aging the low strength fiber at zero stress in either 85° C, deionized water or in high humidity (85° C, 94%RH) has been evaluated using dynamic fatigue in tension. After aging in either environment, the strength is found to increase and flaws are found to grow more slowly than flaws in unaged fibers. Both results show that aging actually improves the mechanical behavior of the large flaws that control the strength of fibers in cables.

A serious concern in the fiber optics industry is the low strength of fiber in connectors, frequently as low as 10% of that of the original fiber. The main reason for this low strength is that the stripping and termination procedure exposes and abrades the bare glass surface. Several fiber manufacturers have recently introduced a fiber construction which can greatly improve the mechanical reliability of fiber in connectors. The actual constructions from the various manufacturers vary in detail, but all have one common feature, a primary organic coating which remains in place when the secondary coatings are removed in preparation for terminating the fiber into a connector. In order for connectors to be successfully glued to this coating, the coating must be hard and well adhered to the glass surface. The coating is generally thin, typically about 10 pm. With such a coating the bare glass surface is never exposed when the fiber is stripped and terminated, and thereby retains its strength and mechanical reliability. Data will be presented on the strength of terminated fiber with and without such permanent, primary coatings.

Confident estimation of the lifetime of fibers in different service conditions requires the accumulation of a considerable body of measurement data. One must first define the expected worst-case service conditions with respect to the environment, and then test in these conditions. An experimental program aimed at defining the effects of adverse environments in achieving long service lifetime of optical fibers in tension and bending configurations was conducted. Both static fatigue & dynamic fatigue data were taken and analyzed for commercially available optical fibers. The fibers were tested in 85° C and relative humidities of 45% & 94% for bending and in 23° C and humidities of 45% & 90% for tension applications. The resulting parameters were compared with each other and were shown how they may be utilized for lifetime prediction.

Kilometer lengths of optical fiber have a much lower strength than short lengths due to occasional defects of an extrinsic nature. The fatigue properties of these defects are hard to study due to their rarity. Subthreshold indentation flaws in silica optical fibers (/. e. Vickers indentations produced under sufficiently low load to avoid radial crack formation) have been shown to exhibit environmental fatigue similar to "pristine" silica fiber. Thus the indentation technique may be used to introduce controlled flaws into the fiber that model the strength limiting defects found in long length specimens. This paper presents the results of fatigue studies on subthreshold indentation flaws that have strengths of up to ~ 1 GPa (typical of proof stress levels).

Several fiber contacting devices used in the fiber optic industry rely on the ability to transmit light through the protective polymeric coating surrounding the glass fiber. These include fiber identifiers, local injection and detection systems, and optical taps. Optimal operation of these devices may require removal of the inks used to color code the fiber. This paper addresses the question of whether the solvents typically used for color removal affect the strength of the fiber. Since strength is strongly correlated to fiber reliability, operations which degrade fiber strength are of great concern. Test results show no measurable strength degradation after color removal, regardless of stripping technique. The long term reliability of fibers in the field is therefore unlikely to be affected adversely by removal of the ink layer from fiber coatings.

This paper suggests how to calculate lifetime for a fiber under constant stress. It outlines the theory behind the experimental principles used in evaluating fiber parameters needed in lifetime formulae.

The induced loss in optical fibers during "in situ" radiation as well as fiber recovery after the irradiator has been shut down is influenced by several factors. These factors include material composition of the optical preform, which implies both core and cladding of the fiber, and the fiber draw conditions. In addition to the material characteristics, the system’s environmental parameters such as temperature, operating wavelength, total ionizing radiation dose, and radiation dose rate are also factors. Our research has addressed radiation test results, both "in situ" and after radiation, on single mode fibers operating at 1300 and 1550 nanometers. This research investigates the damage mechanisms associated with optical preforms with and without phosphorus in the cladding and with enriched oxygen in the core. Fiber drawing conditions also varied.

Neutron irradiation produces defects in silica glass which could lead to permanent loss in transmission of signals through an optical fiber made from this material. This paper reports on a study aimed at gaining a deeper understanding of the nature of damage caused by neutron irradiation to silica glass optical fibers operating at 1.3//m and 1.55/im. The data obtained so far indicates that the radiation induced damage has less effect on the transmission at 1.3//m than on the transmission at 1.55/im. The implications of this significant observation, and the details of the experimental techniques utilised in this study will be discussed in this paper.

Many potential uses exist for multiple-wavelength optical fiber systems. Numerous DOD, DOE and NASA applications will have radiation survivability requirements. This paper describes the use of Wavelength Division Multiplexing (WDM), Time Division Multiplexing (TDM), and Frequency Division Multiplexing (FDM) to simultaneously measure radiation-induced attenuation of optical fibers due to both steady state and transient radiation over a wide range of temperatures. Sample experimental data and block diagrams of the test configurations are presented.

Assessing the reliability of any product immediately brings to mind a rigorous set of tests and measurements. However, inspection and testing alone cannot ensure product reliability. Fundamental reliability must be designed into the product.

The realization of high speed, wide dynamic range, high, stability analog fiber link for underground nuclear testing requires physical contact connectors. At first the kinds of links and performances needs are given, then we discuss the influence of contact or non contact connectors on the stability and the noise for coherent or non coherent links. The analog fiber optic link with physical contact connectors presents a 4%pp level stability and a dynamic range of 4000/1 or 2500/1 respectively for non coherent links or coherent links. This has been verified as well at laboratory as on a gamma ray pulser with.field equipment.

Adhesiveless mechanical fiber optic splices may provide pullout resistance by gripping onto the bare fiber or by gripping onto the fiber coating. The possibility of creep and thermal expansion mismatch in the plastic coating makes gripping onto the stripped fiber attractive. We have determined that damage to the fiber by a gripping mechanism is measurable but not severe, particularly by comparison to mechanical stripping damage and handling damage. We have also observed fiber failures within such splices when using 900 micron diameter, tight buffered fiber. Torque, generated when the fiber is arranged into loops in an organizer tray, propagates into the bare fiber inside the splice. This torque can cause a fiber to break in torsion after a period of time.

The mechanical performance of fusion splices is quite sensitive to splicing equipment and practices. We observed degradation in fiber strength during fusion splicing by examining effects of splicing practices, fiber types and environmental conditions. Conducting appropriate mechanical testing is therefore essential to understanding the failure mechanisms and assuring the mechanical reliability of fusion splices

This paper describes the variable aperture measurement technique for Mode Field Diameter (MFD) in 1300 nm optimized single-mode fiber. Measurement of macrobending induced loss correlates well with theory for both depressed and matched clad singlemode fiber designs. No significant difference in bending loss is found between depressed and matched clad fibers with the same MFD. For bending radii of 8 mm or smaller, the larger MFD fiber yields significantly high bending loss (>1 dB/cm). The bending loss is negligible for bending radii greater than 14 mm. For datacom applications, it is desirable to select small MFD to avoid excess bending loss.

This paper investigates the criteria for performing accurate spectral attenuation measurements using the cutback technique. It is clear that careful fibre handling, together with the correct choice of both fibre launch optics and cleaver are essential if a cutback precision of less than ±0.01 dB is to be achieved.

It is suggested to neasure nodal poser distribution in fiber with the aid of conputer generated optical elenents, called aodans. Nodans are Batched to orthogonal nodes and cause transfornation of nodal poser distribution to intensity distribution in a focal plane. The theoretical calculation sere carried out of aodan's coupler transfer function and the particular nethod is suggested of its coding into phase - only function. Belevant optical techniques sere provided, the experinental results are reported for the specific case of Gauss-Laguerre nodes in graded-index fibers. The nethods, sorked out, are shosn to be applicable in fiber optic sensors.

This communication deals with the experimental verification of the change of strain sensitivity of a polarimetric fiber optic sensor with temperature. Samples of bow-tie HB fiber were submitted to tensile tests by means of a mechanical testing machine at different temperatures. The experimental results confirm that the observed variations on the strain sensitivity can be correlated to the thermal sensitivity change by means of the expansion coefficient.

Interferometric optical sensors have been shown to possess very high resolution due to the sensitivity of the optical path length to a variety of electrical, chemical and mechanical quantities. We present the design of an integrated optic microdisplacement sensor made of four single mode Ti:LiNbO3 channel waveguides on X-cut substrate shaped to form a semi-asymmetric X junction. The effects of the rotation of the waveguide axis with respect to the principal reference coordinate system and the influence of the fluctuations in the environment temperature have been accounted. The calculated effective index change is dnef/dT = 17.10-5oC-1 for EY-11 mode and dnef/dT = 5.3 .10-5 ° C-1 for Ex11 mode, respectively.

An OTDR system has been developed with dead zone and distance resolution in the millimeter range. This system combines streak camera technology in a sampling streak tube with a fast pulsed laser diode system. The OTDR configuration combines these two instruments into a Fresnel reflection system which precisely locates the back reflection from fiber discontinuities and interconnections.

MIL-S-901 High Impact Shock tests were performed on commercial-grade and ruggedized fiber optic connectors, splices, and switches. Both singlemode and multimode connectors and splices were tested. Only multimode switches were tested. Transient losses of varying magnitudes and durations were observed. Most components suffered no permanent degradation.

The paper discusses technical feasibility of using fiber optics technology for underground mine communication systems. The emphasis has been placed on sensor dedicated systems for methane monitoring, fire detection, and vibration sensing. Communication system included video, voice and data transmission has been proposed. The test procedure and requirements for the fiber optics network in the adverse coal mining are given. The network has been developed and evaluated in a number of underground mine applications. The long term environmental trials and laboratory examinations have resulted in approval fiber optic network for in-mine use.

The mechanical reliability of optical fiber is critically important for many engine sensor applications where the fiber is subjected to cyclic loading, high temperature, and oily, acidic environments. We have investigated the effect of buffer coatings on the cyclic fatigue behavior of fused silica fibers. Aluminum, polyimide, uv- curable epoxy acrylate, and Tefzel coated fibers were tested at room temperature and after exposure to heat and oil. Cyclic fatigue was measured using a test fixture that simulates the motion of a piston in an internal combustion engine. The results indicate that the selection of buffer coating is an important consideration in determining mechanical reliability of optical fibers in this application.

The randomly distributed optical fiber imperfections contribute - along with the source and detector noise - to the signal dispersion and change the bandwidth in optical fiber communication systems. On the other hand a variety of such imperfections appear in currently manufactured fibers, affecting both the geometry of the fiber and its gradient index profile distribution. They seem to be unavoidable even in modern manufacturing techniques [1]. We’ve analyzed one example of such random imperfections: the multimode fiber’s core diameter variations and their influence on the unit signal (pulse).

Novel and practical methods of improving reliability of high temperature measurements in harsh environments are discussed. These improvement methods include: mechanical, optical, electrical and software designs. Discussed are mechanical designs for combustion chambers, gas turbines, and especially corrosive environments. Systems are described which use multi-wavelength algorithms for determining the trustworthiness of measurements. These systems use average and difference calculations of the two wavelengths. Also, hybrid optical and thermocouple sensors are presented.

Acceptance of fiber optic position sensors in aerospace applications will be dependent on the ability to prove reliability of the critical components and full assemblies in the expected environment. Considerations include temperature extremes and cycling, shock, vibration, altitude, humidity, corrosion, etc. This paper will present results to date on testing of sensors under some of these environmental conditions and discuss areas of prime concern toward maturing fiber sensors to full flight qualification

The measurement of optical fiber's mechanical attributes is drawing more focus as deployment of fiber transitions from long-haul applications to those in today's local loop and data networks. Testing was conducted to further the understanding of the impact of environmental preconditioning factors on mechanical test result precision. This investigation, using test samples of 250 micron U.V. curable acrylate-coated optical fibers, primarily focused within and about the constraints for relative humidity as specified in the standard test methods. Differences in some mechanical test results are shown to correlate with different levels in the relative humidity of the environment in which the fibers were conditioned for 24 hours.

With the increased number of fiber-optic couplers in use in network applications, it is imperative that device reliability be ensured. Corning has developed flexible and accurate multi-channel test systems for monitoring performance during environmental testing. One such single-mode system utilizing 90 channels has been demonstrated with a one sigma stability of < 0.004dB over 136 hours of testing.

A model is developed and experimentally verified that allows the accurate prediction of the Bit Error Rate performance of a fiber optic link in the presence of a large number of noise sources. The model may be used as a guide for stress testing of a low Bit Error Rate link to reveal the characteristics of the noises with a much reduced test time compared to previous methods.

Because of the wide deployment of fiber with cables often carrying 100,000 or more voice circuits, even a one minute interruption in telecommunication service can totally disrupt the affected communities. Therefore, service reliability of the telecommunication network is essential in an information-intensive society. One of the major reliability issues is the serviceability of telecommunication systems following a major earthquake. In this paper, we analyzed the mechanical failures of optical fibers from a cable subjected to a major earthquake.

Rapid development of Fiber-In-The-Loop (FITL) systems and FITL technology is bringing new challenges for assuring the reliability of optoelectronic devices. This can be attributed to several factors, some of which include: architecture, cost, useful lifetime of the optical source, and environmental conditions. Presently, relatively little is known about optoelectronic device reliability in the local loop. Thorough studies on the impact of loop applications and environments on the reliability of optoelectronic devices are essential. Although this paper will attempt to touch on most of the factors that need to be considered in any such study, the primary focus will be on the possible impact of loop environments on the reliability of optoelectronic devices and the methods required to help assure their reliability.

Over the last several years, fiber optic couplers manufactured via the fused biconical taper (FBT) process have been extensively used in a variety of fiber optic systems and instrumentation. However, because of the rapid development and deployment of this technology, there is only limited field data available regarding the long term performance and reliability of these components. In this paper some recent results of a such a study on FBT couplers will be reported. The test program consisted of accelerated heat and humidity tests, repetitive temperature cycling, mechanical shock and vibration tests as well as long term shelf tests. A review of the test data will be presented along with an estimate of component lifetimes.