The failure of tightly bent optical fiber under high optical power is observed dynamically with fine time resolution and explained in terms of the behavior of the polymer coating and underlying glass. An abrupt rise in coating temperature stimulates the viscoelastic deformation of the glass. The abrupt bending of the glass is explained by the ability of highly quenched silica to deform at low temperatures. There is no evidence of thermal runaway of the glass core. Coating decomposition is self limiting with no visible flame.

Failure analysis of fiber optic cables, components and devices from manufacturing operations, installation and field deployment has been important in reliability assurance for fiber optic communications networks. In this overview presentation, we consider optical fiber transmission failures in fiber optic cables and optical transmission impairments accompanied by mechanical failures in cable assemblies and interconnecting devices. In either case, failure analyses involve detailed characterization of optical and/or mechanical performance under varying environmental conditions such as temperature and humidity. In the case of optical transmission failures of fiber optic cables, we show that the environmental history of the cables and the thermomechanical response of buffer tube materials are of critical importance in understanding low-temperature transmission loss due to thermally-induced fiber microbending. In optical transmission impairments accompanied by fiber mechanical failures of cable assemblies and interconnecting devices, the environmental history along with manufacturing practices used in the production of cable assemblies determine the performance and reliability in the field. For cable assemblies with fiber mechanical failures, fiber break source analysis (fractography) has many challenges in the analysis of fiber breaks where fiber fracture surfaces are readily accessible. However, it has been practically impossible to perform break source analyses in cases where fiber fracture surfaces are not accessible within cables and interconnecting devices. Thus, in this presentation, we review a series of failure analyses performed to identify the cause(s) of high insertion loss and reflectance failures of cable assemblies. An essential component of these failure analyses was the development of new methods for accessing fracture surfaces of broken fibers within connectors. These new methods involve chemical and thermal treatments to preserve all features of fracture surfaces and, therefore, evidence of failure origins.

Silica optical fibers drawn from a common preform and coated with specialty coatings were exposed to zero-stress aging in various aqueous environments for approximately ten months. The strength of the fiber samples was tracked with two-point bend testing. The onset of an aging “knee” was observed for some fiber samples while other coatings offered enhanced protection from the effects of moisture-induced strength degradation.

Polymeric coatings are often used to develop various thermally tunable FBG based devices. Coatings on FBGs can be intended for protection, improvement of thermal sensitivities, special spectral shaping etc., and the quality of the coating on the FBG deserves special attention. For example, the adhesion of the polymeric coatings to the silica based optical fiber plays an important role in the wavelength response characteristics of fiber Bragg gratings during thermal tuning. In this paper, we theoretically investigate the effect of adhesion and the non-uniformity of the coating thickness on the thermal tuning process of FBGs. Experiments were done to qualitatively analyze the influence of adhesion. However practically it is very difficult to quantify the percentage adhesion and quality of coatings for experimental verification. Therefore a methodology based on finite element analysis has been utilized for theoretical investigation of the effect of adhesion of polymeric coating on the performance of FBG based thermally tuned devices. Three-dimensional finite element simulations were carried out. Spring elements are used to inter connect the nodes of the meshed models of optical fiber and coating. The effect of adhesion is studied as a function of spring stiffness. The effect of non-uniformity in the coating thickness in the circumferential direction was also studied.

The inert strength of carbon-coated optical fibers (hermetic fibers) has been observed to be less than that of standard polymer coated optical fibers. A scaled version of the of the carbon-coated optical fiber was developed in the laboratory and used in an experimental investigation of the mechanical properties of this system. The microstructure and phase similarity between the scaled system and the optical fiber was established using Raman spectroscopy. The mechanical properties, residual stress in the film and the fracture toughness of the scaled system were determined using nano-indentation. A fracture mechanics model was developed to explain the mechanism of this strength reduction. The model, based on the cracking of thin films in residual tension, will be used to predict growth of flaws from the carbon film and penetrating into the substrate. The model can be applied to all brittle coatings where delamination of the coating is not observed. Conditions under which cracks in the carbon film propagate into the substrate were investigated using a recently developed superposition scheme. Possible methods of crack arrest will be discussed.

The demand of telecom operators for a 15 year lifetime of their systems is imposing a big challenge on component manufacturers. It means that also for optical connectors - which are used in large numbers in DWDM systems - the wear-out region must not be reached even after 25 years. However, how can it be shown that a connector will live for more than 25 years? Different approaches are possible: Collection of field data can supply information on the statistical failure rates at operating temperature. Accelerated aging tests (often simply called reliability tests) try to simulate aging under defined conditions. Our focus is on the reliability qualification according to the PAS (publicly available specification) IEC 62005-9-2 which is based on the co-work of Siemens with the connector manufacturers and assemblers Corning, Diamond, Huber+Suhner, Molex and TycoElectronics. This standard should now be overworked with the help of the results of the first common testing program which has recently been carried out by the Siemens ICN "Center for Quality Engineering".

Static fatigue of bare indented fibers in different environments was studied. It was found that the n-value in different pH-solutions did not significantly change and was higher than that for strong fibers and lower than that for bulk samples in similar conditions. All lifetime reduction with a pH increase was due to a change of the B-value. The results obtained were used for evaluation of the lifetime of weak fibers for different service environments.

Due to the potential of high data rates up to several Gb/s, low electromagnetic interference sensitivity and weight reduction capabilities, in future, optical data transmission will become standard in airplanes. The requirements on the necessary optical components that have to be operated in airborne environment in general are extremely high. In addition, airframe manufacturers are interested in low cost components. An example for such an optical component is a star coupler for data distribution, in particular, a device made on base of polymers. The applicability of such 4x4 polymer star couplers under extreme environmental conditions was investigated. The investigations were made at temperatures from -40 to +80 °C and up to 98 % humidity. Different types of housings were tested (polymer, metal, ceramic). It was found that housing of the polymer couplers is required necessarily, since non-housed components exhibit a large insertion loss increase of up to 0.5 dB during temperature variation. Best results were achieved with metal or ceramic housings exhibiting a maximum insertion loss increase of approximately 0.1 dB. However, due to a large difference of thermal expansion coefficients of filling and housing material, respectively, ceramic housings mechanically failed (crack formation) and thus metal housings are first choice. The results were also compared to those achieved for commercial 4x4 multimode couplers made of glass and based on fused bi-conical taper technology.

The effects of the fabrication procedure for fibre Bragg gratings (FBG) on the mechanical properties of fibres were investigated by dynamic fatigue tests in two-point bending in a “wet” environment. The results show that both chemical stripping and continuous wave UV irradiation reduced the mechanical resistance of the fibre.

Sensors based on optical fibre materials will be required to tolerate a restrictive combination of physical and environmental parameters for several remote monitoring applications at AWE. These include changes in atmospheric pressure, temperature, humidity, vibration, shock and acceleration, with the sensors being required to operate reliably for periods of up to 30 years with minimal intervention for maintenance. In addition, it is necessary that the sensors can function in the presence of ionising radiation. The sensors are being developed for a number of challenging in-situ physical and chemical measurements. These include remote gas composition analysis, monitoring shape change in compliant materials and the movement of metallic and polymeric components using sensors based on fibre Bragg gratings and interferometric techniques. Reliability issues include the long-term mechanical and optical performance of standard and novel glasses, optical fibres and cables, connectors, couplers, optical switches and Bragg gratings. The durability of materials used in the construction of fibre optic sensing components also requires to be assessed in addition to the epoxy and metallic coatings used to bond these components to a variety of material substrates.

Future thermonuclear fusion reactors need remote-handled equipment for maintenance tasks, since the stringent environmental conditions prohibit direct human interventions. Fiber-optic technology is considered since many years as a potential reliable alternative to conventional electronic transmission lines. Recently, we demonstrated the feasibility of transmitting analog data with a hybrid opto-electronic link at 850 nm, up to total doses of several MGy. For bidirectional communications under these severe conditions, however, we still need to characterize the corresponding photo detector' response and design an adapted radiation tolerant amplifier. Moreover, the neutron sensitivity needs to be assessed as well, since this could prevent them to be stored inside the bioshield during the plasma burns. We therefore assessed the radiation response of commercially available p-i-n type Si-detectors, on line, at a constant temperature of about 60°C, first under gammas rays up to a total dose of about 10 MGy, and also under neutrons up to a fluence of about 7•10¹⁵/cm². Similar tests were also performed with InGaAs photodiodes, in order to assess their use in radiation tolerant coarse wavelength division multiplexing (CWDM) transmission architectures. Our results indicate that the response of the detectors under gamma radiation remains almost unchanged. The displacement damage caused by the neutrons steadily increases with the neutron fluence, both in terms of an increased dark current and a reduced photo response. In this paper we also present temperature dependent measurements and hence assess to what extend both ionizing and particle radiation affect the photodiodes reliability.

High performance and high reliability are two of the most important goals driving the penetration of optical transmission into telecommunication systems ranging from 880 nm to 1550 nm. Lifetime prediction defined as the time at which a parameter reaches its maximum acceptable shirt still stays the main result in terms of reliability estimation for a technology. For optoelectronic emissive components, selection tests and life testing are specifically used for reliability evaluation according to Telcordia GR-468 CORE requirements. This approach is based on extrapolation of degradation laws, based on physics of failure and electrical or optical parameters, allowing both strong test time reduction and long-term reliability prediction. Unfortunately, in the case of mature technology, there is a growing complexity to calculate average lifetime and failure rates (FITs) using ageing tests in particular due to extremely low failure rates. For present laser diode technologies, time to failure tend to be 10⁶ hours aged under typical conditions (P_opt=10 mW and T=80°C). These ageing tests must be performed on more than 100 components aged during 10000 hours mixing different temperatures and drive current conditions conducting to acceleration factors above 300-400. These conditions are high-cost, time consuming and cannot give a complete distribution of times to failure. A new approach consists in use statistic computations to extrapolate lifetime distribution and failure rates in operating conditions from physical parameters of experimental degradation laws. In this paper, Distributed Feedback single mode laser diodes (DFB-LD) used for 1550 nm telecommunication network working at 2.5 Gbit/s transfer rate are studied. Electrical and optical parameters have been measured before and after ageing tests, performed at constant current, according to Telcordia GR-468 requirements. Cumulative failure rates and lifetime distributions are computed using statistic calculations and equations of drift mechanisms versus time fitted from experimental measurements.

At the present time, due to their improved spectral characteristics accompanied by low noise and high linearity of current-light output power features, 1.55 μm DFB lasers are key components of analog microwave fibre optical links. These devices are the most frequently used as both the optical source and RF/optical modulator. Especially in the case of direct intensity modulation links, stringent requirements repose on these devices together in terms of performances and reliability, the latter being a crucial issue for the viability of the optical links. This paper deals with the investigation on the reliability of 1.55 μm strained quantum well ridge DFB lasers. Long term ageing tests were performed during 12,000 hours at 80°C ambient temperature and a constant bias current of 140 mA corresponding to 10 mW output power. These tests ended, none failure or decrease of the optical power was observed. A detailed evaluation based on crucial parameters for direct microwave modulation as static characteristics, emission spectra and relative intensity noise (RIN) has revealed only negligible changes after ageing.

This paper reports on the first steps taken by TeliaSonera towards deploying optical performance monitoring (OPM) in the company’s transport network, in order to assure increasingly reliable communications on the physical layer. The big leap, a world-wide deployment of OPM still awaits a breakthrough. There is required very obvious benefits from using OPM in order to change this stalemate. Reasons may be the anaemic economy of many telecom operators, shareholders’ pushing for short-term payback, and reluctance to add complexity and to integrate a system management. Technically, legacy digital systems do already have a proven ability of monitoring, so adding OPM to the dense wavelength division multiplexed (DWDM) systems in operation should be judged with care. Duly installed, today’s DWDM systems do their job well, owing to rigorous rules for link design and a prosperous power budget, a power management inherent to the system, and a reliable supplier’s support. So what may bring this stalemate to an end? -A growing number of appliances of OPM, for enhancing network operation and maintenance, and enabling new customer services, will most certainly bring momentum to a change. The first employment of OPM in TeliaSonera’s network is launched this year, 2004. The preparedness of future OPM dependent services and transport technologies will thereby be granted.

The paper studies the impact of OXC equipment failure in WDM networks with dynamic end-to-end optical circuit provisioning. At the OXC level, equipment reliability is calculated using proven component level reliability models. At the network level, end-to-end optical circuits are provisioned with various levels of reliability, thus offering differentiated reliability to applications. The desired reliability level is obtained via shared path protection (SPP) switching, that provides efficient resource utilization. A selection of representative OXC architectures is examined to assess the influence of various switching technologies on the overall network level reliability. The selected OXC architectures are compared in terms of both the cost of switching equipment and the ability of the network to accommodate incoming circuit requests, while satisfying their required reliability level.

Differentiated Reliability (DiR) is a concept that was recently introduced by the authors. The DiR concept can be applied to provide multiple reliability degrees (or classes) at the same network layer, using a desired protection scheme, e.g., dedicated path protection switching. According to the DiR concept, each connection is guaranteed a minimum reliability degree, or equivalently a maximum downtime ratio, that is chosen by the client. The reliability degree chosen for a given connection is thus determined by the application requirements, independently by the actual network topology, design constraints, robustness of the network components, and span of the connection. In this paper, two protection schemes are used to provide DiR in a WDM network with arbitrary topology: the path protection scheme and the partial path protection scheme. With either scheme, differentiation of reliability is successfully achieved. It is noted that the latter scheme is 10% more resource efficient than the former scheme in providing the desired reliability level. The former scheme is however less complex to manage than the latter.

This work is motivated by interest in analyzing and optimizing availability of optical networks under different protection strategies. Methodology dealing with availability calculation, protection strategies, spare capacity, redundancy and sensitivity analysis is described. A case study calculates the availability of all connections within a long haul US-network using three protection strategies: path protection, span protection and protection-cycles. The distributions of connection down time of the three protection strategies are given. The availability optimization potential is estimated based on analysis of its sensitivity on reliability input data. Advantages and disadvantages of each strategy are compared from the availability and spare capacity requirement points of view.

The principal disadvantage of using Free Space Optical (FSO) telecommunication systems is the disturbing role played by the atmosphere on light propagation and thus on availability and reliability of the link. Atmospheric effects on the electromagnetic waves transmission differ according to the used wavelength. Among these effects, fog is a very important factor in the electromagnetic radiation degradation and especially for the visible and infrared waves. Relationship between the fog characteristics (liquid water content, density, visibility...) and the transmitted signal attenuation for a given wavelength should be known in order to predict the FSO systems performance and link availability. The lasercom literature shows the complexity of the problem related to different types of fog and its inhomogeneity over the propagation path. The problem of atmospheric attenuation for laser radiation in visible and infrared regions was reviewed from an empirical and theoretical point of view. We describe the optical properties of fog calculated from the Mie scattering theory and the particle size distribution. We investigate the laser system performances in presence of fog in 0.4 to 15 µm spectral band from Fascod computation (advection and radiation fog) and from other particle size distributions available in the literature. We compare the extinction coefficient (function of the wavelength) for different particle size distributions in order to see whether the various types of fog may be represented and covered by the models proposed in Fascod. Finally, we consider some particular laser wavelengths (0.69, 0.78, 0.85, 1.55, 5 and 10 µm) used and proposed for the FSO technologies in order to study and compare the effect of fog on equipments operating at these wavelengths.

Free space Optical links (FSO) in visible and infrared wavelengths constitute an interesting alternative to new transmission channels for cordless phone, data-processing networks and high definition television. One finds a choice of varied manufacturers and they propose products whose performances are characterized by a raised rate of transmission, from 2 Mbps to 10 Gbps. But the announced ranges are very important, from 100 to 10 000 meters, in spite of the fact that many manufacturers try to indicate the possible ranges according to time, these indications completely miss standardization and are hardly exploitable because, generally, it is very difficult to know the percentage of time during which a value is reached or exceeded. Availability and reliability of a FSO link depend on used systems but also on climatic and atmospheric parameters such as rain, snow or fog. It is the purpose of our study. Its finality is software which integrates: - Results of a bibliographical search (geometrical, aerosols, rain, snow, fog, scintillation, and environment solar light attenuation), - European integrated surface weather data, hour per hour, over several years (1995-1999). The result is the presentation of the Quality of Service Light version software which allows predicting; starting from the data of equipment (power, wavelength, receiver sensibility), geographical situation of a site in Europe (geographical coordinates, altitude, height/ground) and climatic and atmospheric parameter (relative humidity, ground rugosity, albedo, solar radiation, etc) the availability of a FSO link for the following period (year, the most unfavourable month, 8am to 8pm period and 8 pm to 8 am period. The interruption probabilities for each type of attenuation are also mentioned (aerosols, scintillation, ambient solar light, rain, snow, etc).

Currently the wireless networks are replacing the connection cables via radio or infrared waves. Emission/reception terminals are installed to cover zones in relation with a quality of service. Thus users can be connected to the local area network thanks to an adapter that emits and receives on this network. There are technological radio solutions : Bluetooth, WiFi, and optics constituted by an infrared base and modules. Infrared technology has important advantages: Transmitted data security, radio and medical immunity, etc. Nevertheless, the optical systems seem to present a limit because the network management is based on only one wavelength and several users. The solution suggested, scope of this document, is at a crossroads with the telecoms with optical fibre, optics in free space and data processing domains. Indeed, it is a question, of using WDM technology and transmitting these various wavelengths in free space, using optical Multiplexer/Demultiplexer and optical modules, which are compatible in wavelength. Each mission/reception module has a defined and personal wavelength, with a link with the terminal identification (addresses MAC or IP). This approach has full duplex data rate for a minimum of a dozen Mbps per user for a broadcasting, and hundred Mbps for a line of sight system. The application field for the suggested system is potentially included in the following networks types: WirLAN, WirDAN or WirPAN.

The study of the effect of high optical power on FBGs among different laboratories whitin the COST270 action required to verify the consistency and convergence of Bragg grating measurements obtained by the laboratories involved in COST270. This papers reports and discusses the results obtained during a round-robin for fibre Bragg grating metrology initiated within the COST270 action. This action was undertaken in order to minimize measurement scattering and to reduce the uncertainty in the interpretation of following COST270 round-robin measurements on the effect of high optical power on FBGs. This exercise dealed with the spectral characterization of FBGs written in standard telecommunication optical fibre (CORNING SMF-28) provided by the coordinating laboratory (Ecole Polytechnique Federale de Lausane, Institut d'Optique Appliquee).

Building on recent work, this paper describes the viscoelastic behavior of microstructured polymer optical fiber (MPOF). Previously published fixed frequency dynamic mechanical and thermal properties of the two types of POFs; a commercial, C-type and MPOF fiber prototype B are compared here with multi-frequency data. As expected of viscoelastic materials, results reveal a rate dependent behavior of the fibers where storage modulus (E') increases with frequency at each temperature and the glass transition (T_g) shifts to higher temperatures. A lack of a clear (T_g) and least amount of separation between low- and high-temperature transitions at different frequencies in the C fiber clearly indicate the speciality of the fiber; it exhibits extensive elongation or rather strain-softening beyond the draw-temperature-under-load (DrTUL), which is a highly desired property for optimized hot-drawing. Strain-hardening as exhibited by the MPOF B is a brought-forward effect of the mechanical and thermal histories from its macroscopic deformation during preform structuring and fiber-forming. Polymer entanglements that cause an increase in storage modulus and 'resistive' contraction from 60 to 105°C are most likely to be networked in an orderly manner. Demonstrated again in both types of fiber, DrTUL is critical for load bearing drawing.

Often lightguide fiber processing involves steps that may cause degradation of very high strength or flaw-free, perfect fiber. A very obvious type of degradation is the development of abrasion flaws during handling. Also, heating of a fiber to moderate temperatures (~300-600°C), for instance during the soldering of pigtails, has been shown to result in strength degradation of strong fiber. It has been suggested that the use of HF etching may be a reasonable technique for the elimination of many types of strength-lowering defects. In this paper we discuss early results from the literature on the effects of heating and HF etching on the strength of silica glass and present new results on both.

In this paper we present the result of a sensitive experimental technique used to provide information about the limitations of using organic polymers for fiber-optic high power applications. Optical path adhesives are commonly used in fiber optics assemblies due to their mechanical and optical properties. However, their use in high power applications creates certain concerns about short-term and long-term stability of the adhesive material. We developed an approach for evaluating the effects of high power in optical path adhesives used in applications for fiber-optic devices. We extended far field experimental technique for analysis on a thin polymer layer placed on the tip of an optical fiber exposed to a wide range of optical powers. We found that this technique can be used for both thermo-optical effects evaluation and electronic non-linear contributions to the refractive index of the material. We show how this method permits separation of these two effects, and long term behavior of polymer materials in such applications. This approach could be used for evaluation of wide range polymer materials in photonics.

Free Space Optical (FSO) links offer high bandwidth and the flexibility of wireless communication links. However, the availability of FSO links is limited by weather patterns like fog and heavy snowfall. Microwave based communication links operating at high frequencies (40 - 43 GHz) have similar characteristics like high data rates and needed line-of-sight. Link availability for microwave systems is limited by heavy rain. Combining FSO links with microwave links within a hybrid FSO/microwave communication network has the advantage of added redundancy and higher link availability. Measurements over a period of one year show a combined availability of 99.93% for the climatic region of Graz (Austria) which proves that the combination of both technologies leads to a highly available wireless connection offering high bandwidth.

A number of spectroscopic techniques make use of UV absorbance and luminescence measurements e.g. to characterize materials, for use in medical/pharmaceutical applications, for forensic and sensor applications, etc. Remote detection or monitoring, especially for hazardous environments, benefit from the use of optical fibers. Furthermore many high power applications in medicine and industry are looking to use UV wavelengths. All silica compositions are better able to provide transmission of uv wavelengths, however there have been limitations on their use. Numerical aperture and solarization of the fibers are main concerns. Fibers have been recently developed which can be used for extended periods of time at wavelengths from 193 to 400 nm without serious degradation of their transmission properties (non-solarizing) and with significant broader numerical apertures,[NA] of 0.26-0.30 allowing sampling of larger areas and greater collection of transmitted or reflected beams from materials under test. Mechanical and spectral properties for these new fibers will be presented and compared with the standard all silica fibers. This will include reliability test results at selected UV wavelengths. Possible application areas which would particularly benefit from these high NA, UV non-solarizing optical fibers will be suggested.

An alternative type of 3-port polarization-independent optical quasi-circulator by utilizing a pair of holographic spatial walk-off polarizers (HSWPs) is proposed. This device consists of a reflection prism, three polarization beamsplitters cubes, a pair of HSWPs, a Faraday rotator, and a half-wave plate. The operating principles, the characteristics and the performances of this device and HSWPs are discussed. In order to show the validity, the prototype device operating in 1300nm is assembled and tested experimentally. The merits of this design include polarization-independence, compactness, high isolation, and easy fabrication. It should also be possible to design the device operating at 1550 nm wavelength range.

Optical Access Networks based on Optical Ethernet (OE) architectures represent a simple and low cost solution for eliminating the bandwidth bottleneck between high speed Local Area Networks and optical Metropolitan Area Network core. Transparent optical Network Elements (NE), e.g. optical switches, can be successfully introduced in current OE networks to provide an adequate level of resilience and reduce the overall network cost. However network control and management plane must be extended to administrate the optical network elements. This paper shows a hardware and software implementation of a 1:1 optical span protection scheme for OE network based on optical switches triggered by failure detection. Detection is obtained by three different methods based either on hardware or software mechanisms. Link state is updated both at the switch controller and control manager through, respectively, Link Management Protocol (LMP) and Simple Network Management Protocol (SNMP) messaging implemented by a novel Extensible Markup Language (XML) Multi Protocol Framework (XMPF). Experimental results show that a recovery time in the millisecond range can be achieved and network state is correctly synchronized in all the network elements.

The lifetime of an optical fiber depends on its environment. Previous work extensively measured and characterized the separate effects of humidity and temperature on the fatigue parameters using three different kinetics models, but the combined effect has not been determined in detail. In this work, the details of how the fatigue parameters vary with temperature in a humid environment were investigated. It was found that the kinetics model parameters were different from values obtained elsewhere in liquid water. This may be the result of differences in the apparent activation energy for fatigue in liquid and vapor environments.