UV transmission and radiation-induced attenuation were determined for fibers drawn from improved silica core/fluorosilicate clad preforms with variations in fiber coating, draw temperature, tension, and speed.

A systematic study was made of the influence of transmitted optical power upon steady-state, Co-60 radiation-induced attenuation in pure silica core optical fibers near 865 and 1300 nm at -55°C. Single mode and multimode glass and polymer clad fibers were studied. The power-density dependence of attenuation fading following irradiation was modeled in terms of nth order kinetics. The analysis reveals that at low-power density bimolecular-type processes dominate, order n=2, while at high-power density high order, photoenhanced processes prevail, of order The threshold for these and other effects is near .4 mW/cm2.

Fiber optic delay lines under =100 kpsi bend stress at 22 and -55°C were evalu-ated at 1300 nm during and after Co-60 irradiation and compared with similar multi-mode, low-OH, pure silica core/fluorosilica clad fibers under =10 kpsi bend stress. A very small, positive, =15% change in fiber attenuation (dB/km) was observed that suggests under high bend stress optical fibers may incur somewhat more radiation-induced attenuation than unstressed fibers. However, the influence upon overall radiation susceptibility of photonic systems deploying fiber optic delay lines with lengths up to 100 meters and under =100 kpsi stress should be negligible.

The radiation sensitivity of single mode polarization maintaining optical fibers have been studied using fibers optimized for operation at 850 and 1300 nm. These fibers have Ge doped cores and rely on stress induced birefringence for their polarization retention. We have also measured a non-polarization preserving (PP) single mode fiber of similar doping to the PP 850 fiber as a comparison. The response of the 850 nm fibers is consistent and is inverted with respect to temperature. Thermal annealing of the radiation damage is not the dominant recovery mechanism. The 1300 nm PP fiber shows normal temperature response. Induced attenuation is much higher in 850 than in 1300 nm fibers. For FOG applications with a radiation tolerance requirement, fiber selection beginning with fiber optimized for operation at 1300 nm is indicated.

Low OH, high CI pure silica core optical fibers have been irradiated at several temperatures and using different operating power levels. The growth data to 10 krads at 1320 rads/min irradiation rate have been measured along with the recovery out to 1-2000 seconds. The data have been analyzed to determine the effect of temperature for high and low power levels. This analysis and the implications on the mechanisms of defect growth and recovery are presented. A new set of experiments are proposed for a broader set of fibers specially prepared to enable further elucidation of the mechanisms especially the presence of high CI levels in some of the best rad-hard fibers.

The radiation induced loss in optical fibres is initially determined by the preform properties, the fibre draw conditions, and the radiation test parameters. We have found that some fibres change their radiation sensitivity considerably after expsoure to high dose values (10⁵ - 10⁶ rd) and explain this with radiation damage, i.e. the production of new precursors for colour centres in concentrations comparable or even higher than those of the initial ones. To get further informations about the nature of eventually generated new defects, we compared the transient induced loss of damaged and undamaged fibres as well as measured the wavelength dependence of the induced loss with increasing 60Co gamma dose. Some fibres (polymer fibres and OH rich fibres with pure SiO2 core) showed considerable permanent damage, whereas Ge doped fibres (single mode as well as graded index) remained nearly unchanged up to 106 rd.

The sensitivity of long wavelength single mode fibers to ionizing radiation plays an important role in fiber optic component selection for military systems. Our research efforts have concentrated on low temperature and minimum optical power to reduce the annealing and photobleaching attributed to these operating conditions, and specifically focus on the damage mechanisms associated with fiber material compositions. Our test results indicate that the presence of phosphorus in fibers increases the induced attenuation during irradiation and the fibers display continual damage after irradiation. Without the presence of phosphorus, standard germanium doped core single mode fiber as well as an oxygen enriched germanium doped core fiber exhibit similar recovery characteristics. This research report will address the fiber sample composition, the test conditions, the test setup, and the test results.

The transmission performance in a Co-60 radiation environment of a polymer clad/pure silica core fiber is evaluated near both the 850 and 1300 nm telecommunications windows, and at +22 °C and -55 °C. The evaluation includes an in situ measurement of radiation-induced loss up to 10 krad and fading of this loss to 105 seconds after cessation of exposure. It is found that at room temperature superior radiation resistance is afforded near 850 nm. However, in spite of larger intrinsic losses, it was found that at -55°C lower total attenuation during irradiation and up to several hundred seconds after exposure is available at the longer-wavelength window. Furthermore, as average transmitted power increases, the doses during irradiation increase and the times during recovery decrease for this period of superior performance. These results suggest the longer wavelength may be better suited for shorter transmission links intolerate of momentary interruptions.

Long term reliability of optical fibers is extremely important for fiber optic system performance over a long period of time in different application environments. The reliability of silica based optical fibers and heavy metal fluoride optical fibers is consid-ered. The mechanical reliability and the effect of radiation in optical performances are discussed in this paper.

The fabrication, performance characteristics and reliability results of distributed feedback semiconductor lasers are described. Our results show that the lasers exhibit excellent light emitting lifetime and spectral stability for commercial lightwave system application.

An impressive technology now exists for the fabrication of photodetectors based on InGaAsP/InP heteroepitaxy. Excellent performance is obtained over the range from 1.0 pm to 1.7 gm, making these devices ideal for optical fiber communication applications. In this paper, we will review the state-of-the-art of InP based photodetectors with emphasis on their reliability. We will discuss some of the known failure mechanisms and describe measures taken to eliminate them. We will show results of reliability experiments performed in our laboratories on photodetectors. These devices have demonstrated extrapolated failure rates below 1 FIT and are now used in submarine cable systems and other applications with demanding reliability requirements.

In this paper, recent efforts to characterize the reliability of passive fiber optic interconnection components, such as, single mode connectors, fused-tapered couplers and wavelength division multiplexers are reviewed. These components, having been tested under a variety of mechanical and environmental conditions, showed no degradation in optical or mechanical performance.

Undersea lightwave systems represent a fascinating and challenging application of photonics engineering. Economy, transmission quality and long-term reliability are the hallmarks of these new systems. The optical fiber medium offers very high channel capacity for voice and all other digitally encoded signals. The high capacity results in low cost per channel. Concerning transmission quality, today digital transmission on undersea cables carries signals halfway round the world with quiet, virtually error - free performance. Furthermore, the short, direct path of the undersea route minimizes signal delay, making a significant contribution to customer satisfaction with voice, data, video conferencing, and other interactive services. We needed to achieve these important advances in economy and quality of transmission, and yet deliver systems with the traditional 25 year life and high reliability. This was the dilemma, to achieve extraordinarily high reliability with technologies which lacked extensive high-reliability background. Redundancy in several forms allowed us to introduce this advanced technology with high confidence of meeting the goal of 25 years of reliable system service. Following some historical notes on undersea cables, we describe the forms and levels of redundancy used in AT&T's SL Undersea cable systems. We then indicate how redundancy was implemented and it's impact on system reliability. Finally, we do a bit of crystal gazing concerning redundancy and reliability in the rapidly evolving optical undersea cable network.

TAT-8, the first transatlantic optical fiber system, was installed in the summer and fall of 1988 and went into service in December of that year. The design life of the system is 25 years, with an objective of no more than three ship repairs caused by spontaneous sudden or gradual changes in its component parts. The experience with TAT-8 during its first year in operation (and, for somewhat shorter times, with systems of the same design installed in the Pacific) is reported. Based on that experience, projections of likely future performance are made. Some of the failure modes that were of concern during the development, the measures taken to exclude them, and the degree to which these currently appear to have been successful, are discussed. As I write this abstract in the spring of 1989, I am imbued with the sincere hope that there will not be much in the way of specific events to report and the somewhat conflicting question of how I will provide an interesting talk if that hope is fulfilled. Questions that will be of interest are whether the redundancy incorporated into the system appears to have been required, whether there are any indications of changes with time, and any lessons that can be abstracted to be applied to the next generation. Assuming favorable results, there is the challenge of reporting these in a sufficiently modest manner, to prevent invoking the well known jinx associated with overconfidence in these matters.

This paper reviews fiber optic system reliability issues from three different viewpoints - availability, operating environment, and evolving technologies. Present availability objectives for interoffice links and for the distribution loop must be re-examined for applications such as the Synchronous Optical Network (SONET), Fiber-to-the-Home (FTTH), and analog services. The hostile operating environments of emerging applications (such as FTTH) must be carefully considered in system design as well as reliability assessments. Finally, evolving technologies might require the development of new reliability testing strategies.

Results are presented on the in-situ radiation response of three commercial hybrid optical receivers of the type used in high speed fiber optic networks. When subjected to a 2.5 MeV pulsed electron beam, a receiver that contained a GaAs MESFET was found to exhibit transient effects in response to a dose as low as ~50 Rads. Two other receivers containing no GaAs FETs suffered little or no amplitude perturbation on exposure to 200 - 400 Rads(GaAs) per pulse. The radiation response of the first receiver is shown to be consistent with the long term transient response of conventional GaAs MESFETs. Implications for circuit design and for several high speed data buses are discussed.

The National Communications System (NCS) is responsible for defining reasonable enhancements that could be applied to commercial common carrier (or carriers'-carrier) fiber optic systems that will be leased or owned by Government agencies and that may be used for National Security and Emergency Preparedness (NS/EP) purposes. This paper describes enhancements recommended by the authors for making fiber optic long-haul systems more survivable against both man-made and natural disasters. For a limited nuclear environment, outside of the blast region where buildings and personnel would be expected to survive, involving surface and in-atmosphere nuclear bursts, the vulnerability of optical fiber waveguides to fallout radiation is a primary concern. An assessment of fiber darkening from gamma radiation, based on a review of unclassified literature, is presented. For exoatmospheric nuclear bursts, the fiber optic system is exposed to high altitude electromagnetic pulse (HEMP) radiation. Other man-made disasters include sabotage, fires, accidents, and unintentional dig-ups. Natural disasters considered were floods, earthquakes, lightning, temperature extremes, rodents, etc.

Stability tests were performed on three types of tests setups -- a multimode setup with a laser, a multimode setup with a light emitting diode, and a singlemode setup with a laser. Each of the setups used a coupler for source monitoring. The multimode setup with 'a laser was postulated to be affected by modal noise. Also, stability as a function of ambient temperature changes was examined in the singlemode setup.

Vibration tests were performed on commercial grade fiber optic connectors and splices. Both singlemode and multimode components were tested. Sinusoidal vibrations up to 500 Hz and random vibrations up to 2000 Hz were applied. Analog modulation was negligible and no permanent damage was observed.

Temperature and humidity tests were performed on commercial grade fiber optic couplers, connectors, splices and optical,fiber. Both singlemode and multimode components were tested. Temperatures ranged from -54°C to +65°C or +85°C depending on the component application. In the humidity tests the relative humidity was maintained at greater than 95 percent above 20°C. Changes in optical transmittance of varying degrees and permanent damage were observed and recorded.

Using fixed power margins in fiber optic system power budget calculations does not adequately account for the nature and complexity of a fiber optic link. In an adverse environment scenerio the power margin must be sufficient to guarantee link operation throughout all expected conditions. A variable margin dependent upon the nature and number of the components in the link provides a more acurate estimate of the margin required for a link than a fixed margin. One particular method of estimating each components portion of the environmental margin is presented.

Samples of a 140/100-micron single-fiber optical cable* were tested in a flame environment to determine 1) the effectiveness of Nextel 312** ceramic-fiber sleeving for providing thermal protection to the cable and 2) the effects upon light-signal transmission. The optical cables were tested with and without the protective sleeve (or jacket) in a standard 6-inch diameter propane burner i'2 at flame temperatures ranging from approximately 450° to 860°C (842° to 1580°F). The flame tests were conducted with and without external vibration being applied. During a 30-minute test run of a jacketed cable at a nominal flame temperature of 500°C (932°F) without external vibration applied, the optical intensity (-15 dbm) of the signal passing through the fiber was essentially unchanged, and the signal was uninterrupted. In addition, the shape of the 1-megahertz square-wave output signal was unchanged, as observed on an oscillope. The same test specimen was re-tested for another 30-minute period without vibration at a higher nominal temperature of 735°C (1355°F). During this second run, the output signal was again received continuously without decrease in optical intensity or distortion of the square-wave shape. However, the signal was finally lost due to mechanical failure of the single optical fiber when the specimen holder was removed from the burner after the second run. When the ceramic sleeving was cut open along its length, inspection showed that all of the plastic materials used in the cable construction had completely burned and decomposed. Except for a small amount of white ash, only broken pieces of the glass fiber were found inside the ceramic sleeve. It became evident that the glass fiber alone had survived throughout two 30-minute flame-test runs and was able to pass the signal without interruption or loss of intensity. The results of other test runs are discussed, in which optical cable samples were tested with and without protective sleeving, and with external vibration applied.

This paper reports a simple method for testing hydrogen generation in fiberoptic cables by using a 1240 nm OTDR. The performance of an OTDR module operating at 1238 nm is compared to spectral attenuation measurements around the hydrogen peak located at 1244 nm, and it is found that the OTDR is able to detect approximately half the peak level. This ratio is fairly constant at peak hydrogen levels exceeding -0.15 dB/km. The OTDR shows excellent stability vs. time and temperature which makes it an excellent tool for field measurements. Some test cables, mainly submarine types, have been tested with this OTDR module and compared with 1300 nm OTDR measurements. Local hydrogen sources along cables have been identified by this procedure from the OTDR return signals.

In this paper, we discuss the Navy specified fiber outer diameter(OD) and connector/ferrule inner diameter(ID) tightened tolerances, required maximum insertion loss per connection, and use of one ferrule termini size with both multimode and singlemode fibers. By briefly discussing these areas, we intend to provide pertinent information regarding the rationale for the decided Navy requirements, trade-offs involved, and related items which support the development of singlemode, short haul, highly concatenated, shipboard systems.

The Navy desires to install shipboard fiber optic cables which will exhibit a service life of at least 40 years. The cabled fiber must provide predictable performance and display a high degree of reliability under adverse mechanical and environmental conditions. The performance and extended lifetime properties of the shipboard cable can be characterized through reliability models and service design curves. These models are based on fracture mechanics test procedures conducted under different loading configurations and environmental conditions. This reliability information will provide insight into the selection of suitable shipboard optical cable installations and will lend predictability to operational service life.

Actually, available polymethyl tnethacrylate core plastic optical fibers present as attenuation versus wavelength characteristic strongly dependent on the wavelength is the red region of the spectrum, where the light emitting diodes are currently at hand. This paper shows how to calculate the penalty on fiber length caused by the AlsGai_aAs light emitting diode spectral characteristics, when the peak emission wavelength of this source is not optimized for utilization with a plastic fiber.

Low-cost optoelectronic components in non-hermetic packages are now required for use in the local loop, and these components will be subject to humidity-induced failure mechanisms. The results presented in this paper show that it is possible to provide some protection for the photodiode against the effects of humidity by means of an organic coating. Photodiodes with three different organic coatings were tested at 85C/85% relative humidity, and all survived longerthan uncoated control photodiodes. One of the coatings was superior to the other two, and photodiodes with this coating may have adequate reliability for some local loop applications. The temperature and humidity acceleration factors for uncoated photodiodes were determined. The temperature acceleration factor was found to be low (equivalent to an activation energy of 0.2eV, instead of the more usual 0.6eV). Failure analysis of failed photodiodes, which included Auger analysis of corrosion products, showed that failure was due to oxidation of the InP surface.

The effects of neutron irradiation on several properties of both single and multiple stripe laser diodes have been examined. Prior to fast neutron irradiation, total light output as a function of laser current, threshold current, near field pattern, far field pattern, and laser output wavelength spectra were measured at roan torperature. These measurements were then repeated at intermittent neutron fluence levels. It was observed that the threshold current increased with neutron fluence for all devices examined. In contrast, neutron irradiation had only an indirect effect on the remainder of the laser diode properties in that the higher currents required for operation after irradiation caused variations in these properties.

We report here the results of irradiating LiNb03 optical devices. Various types of devices were irradiated. These include wave guides, bidirectional couplers, and delta beta switches. The radiation used was gamma rays and electrons. The experimental techniques and the results are described below.

The mechanical reliability of long lengths of optical fibers is controlled by large flaws that occur so infrequently that they are unlikely to appear in the short lengths of fiber ordinarily tested in the laboratory. Current mechanical reliability predictions are based on data obtained from short lengths of high strength fiber, but there is some concern that these data may not apply to the critical, large flaw sections. We have produced long lengths of low strength fibers with narrow strength distributions by directing a jet of abrasive particles against the fiber surface before coating. Static and dynamic fatigue testing of the low strength fiber showed that the crack growth exponent, n, increased with decreasing strength. Since larger values of n are associated with slower crack growth, the use of smaller n values obtained from high strength fibers results in conservative reliability predictions.

The long-term mechanical reliability of optical fibers is controlled by their strength, fatigue resistance, and zero-stress aging behavior. Understanding the effect of the chemical environment under zero stress on the subsequent fracture strength of optical fibers is important because optical fibers in service are likely to encounter water and other chemical species while exposed to zero or low stress conditions. To determine the effect of zero stress aging on polymer coated optical fibers, we used several fibers which were coated with various UV-curable polymer coatings. The results clearly showed that the strength, fatigue resistance, and aging behavior varied significantly among these fibers. Strength reduction took place after aging in water. Such reduction was both temperature and time dependent and was also affected by the polymer coating. The initial degradation in strength may be partially or fully recovered through drying. However, the degree of recovery became less with increasing storage time at zero stress. A change in the fatigue resistance of these fibers, which was modified by the coating material, was also observed.

Fiber optic couplers have been developed with optical performance specifications that are close to the theoretical achievable limits. However, the development of devices packaged to withstand excessive shock and vibration levels encountered in military and some industrial environments has yet to be fully realized. In this paper details will be given of a new packaging concept for the ruggedization of 2X2 and star fiber couplers that show improvements in the pull out retention force in addition to the shock and vibration performance.

A novel lensed termination system has been developed for the use of fiber optic cable in military cylindrical connectors. Besides tolerating the great variation in longitudinal position experienced by contacts in standard cylindrical connectors, the new termini incorporate a "PBF" crimp attachment to both the fiber and the cable strength members which confers great resistance to mechnanical and environmental extremes. In the test program reported here, five different groups, of ten terminus pairs each, were subjected to terminus insertion force, optical insertion loss, terminus removal force, temperature life (1000 hours at +150 C), engagement force, separation force, thermal shock (-55 to +150 C), tensile strength (19 lbs.), durability, random vibration (24 hours, 39.6 g's rms), shock (300 g's half sine, 3 msec), salt spray, cable flex, cable twist, cable retention (38 lbs.), sand and dust, humidity, altitude immersion, fluid immersion in 10 different fluids, and repeats of the tem-perature life and tensile strength tests. In every case the changes in insertion loss were less than 0.5 dB, and in most cases the changes were less than 0.2 dB. Of additional interest were tests directed specifically at the crimp fiber attachment, which was subjected to parallel testing, with epoxy terminations, in thermal shock, tensile force, and severe cable twist tests. The results showed that whereas the epoxy terminations showed the typical susceptibility to bond failure in each test, with moderate to drastic pistoning, the new crimped terminations showed little or no pistoning at any time.

In recent years the reliability of optical fibers has become of great concern due to military, medicaland other specialty high performance applications. With the nearing promise of the local loop and its inherent requirements for a robust fiber, even the telcom market has come to value research on stronger, more fatigue resistant fibers. With the extension of Hard Clad Silica (HCS®) technology to all silica optical fibers, a new singlemode fiber (smf) structure has been developed with enhanced reliability. A thin, hard, adherent, polymeric coating is placed between the silica cladding and the typical acrylate buffer coating. This paper presents results on the mechanical properties of this new singlemode fiber and compares it with the commercially available smf type. Dynamic strength, Weibull mean strength and slope, and static fatigue resistance, especially after zero-stress aging, are superior for the new fiber over the conventional smf fiber. Compared to commercial smf, the new fiber can withstand high stresses in moist environments for 40-60 times longer. More significantly after zero-stress aging in boiling water, the commercial smf break in <1 sec at stresses above 2.0 GPa (290 ksi), while the new fibers would still have expected lifetimes at 2.0 GPa stress of >9 years. These results make these fibers very useful for high reliability, high strength, long-haul fiber applications.

An experimental methodology is presented for determining the allowable design stress on an optical fiber in service. The design stress must allow adequate static fatigue lifetime at high reliability. The experimental methodology and data analysis presented here have been used to successfully model static fatigue behavior in a wide range of environments in tests of up to 44 months duration.

A two hundred meter length of 100/140 micron Graded Index (GRIN) optical fiber was exposed to a beam of relativistic Fe ions, with an energy spectrum similar to that of galactic cosmic rays between 10 and 600MeV/amu, for 9.1 sec with a flux 2E7 ion/cm2 sec, for a total fluence of 2E6 ion/cm . No change in the optical characteristics of the fiber was noted in a measurement with a noise floor of less than 0.5dB/km. The major source of noise was due to vibration of the fiber. This exposure represents the total fluence of highly energetic Fe ions that would be expected to accumulate in space over a 100 year period of time due to the naturally occurring galactic cosmic rays GCR. The measurements were performed in early 1987.

Susceptibility analysis of optical fibres in application environment reveals that the performance depends directly on component specialization 1,2,3. The major task for environment oriented component specialization is to remove the harmful results of ex-cessive environmental sensitivity on the whole system. We are interested here in the design of special fibres of very high reliability for narrow band/wideband communication channels ans sensory/telemetric systems with depressed (or enhanced) sensitivity to specific environmental reactions or measurands. A considerable interest exists in modifying the properties of standard optical fibres by incorporating additional desensitizing/sensitizing layers or dopants to reduce (or enhance) a given effect.

Performance of low-loss, high strength optical fiber splices is analyzed using a parametric model that relates losses with the critical splicing conditions such as initial misalignment; prefusion condition; pressure applied between fiber before fusing, PA ; fusing temperature, T ; and time, t. Fusion time is optimized for minimum splice loss via considerations of the forces due to PA, thermal expansion, and surface tension of the viscous melted glass in the fiber. In silica fibers, the critical conditions of splicing for a minimum t and splice loss are: PA 20 g and T 2000 to 2150 °C. Although t can be reduced further at higher T, the tensile strength of the spliced zone becomes poor. For the best initial alignment and prefusion conditions achieved in the laboratory, fusion splices show an average loss of 0.12 and 0.02 dB for 10/125 pm and 50/125 pm fibers, respectively ; and a maximum tensile strength of 0.65 kg when fused at t of the order of (1.8-3.0) sec. Fiber breaking strength can be increased fivefold, provided the spliced zone is reinforced with chemical adhesive followed by polyethylene(PE) shrinkable tube and solid packing. Prooftesting of fused fiber splices subjected to a variety of adverse conditions (extreme temperatures, humidity, and submersion) assured the long-term reliability of the reinforced splices. Performance of fusion splices thus fabricated and lifetested are discussed.