Strength-Probability-Time (SPT) diagrams provide an intuitively pleasing method for presenting reliability data based on extrapolations from accelerated fatigue testing data. If power-law crack growth kinetics are assumed the calculations required to generate the SPT diagram are particularly simple. However, if exponential or other more complex forms are used, this is not the case. If the accelerated data are for dynamic fatigue measurements (strength as a function of stressing rate) the SPT diagram can only be determined after numerical integration of the crack growth equations, followed by non-linear regression to the fatigue data. However, we have developed software to perform this task. In this paper we describe the methods used and show sample results of lifetime predictions using SPT diagrams. Also, the effect of using different crack growth kinetics models on predicted lifetimes is discussed.

Optical fibre is often required for long-term applications in harsh environments, eg. underwater cables or aerial cables in snowy areas. However, stress corrosion or the growth of cracks present on the surface of the glass results in the failure of the fibres, especially if they are to be deployed in humid areas and bearing a static stress. The presence of a fatigue limit, a stress under which the crack does not grow has not been established in pure silica glass, in contrast to borosilicate and the soda-lime glasses. A method to check the presence of a fatigue limit was developed by Gupta¹ by studying the relation between the power and exponential laws of crack growth. Here, dynamic fatigue tests were carried out to estimate the fatigue parameters. The limiting stress is found and is compared to static fatigue results from tests carried out under hot water to accelerate the corrosion process. The extrapolation of the static fatigue stress for a time of 25 years predicts a failure stress that is higher than the fatigue limit.

In addition to the numerous assessments presented in literature of the radiation-induced optical property changes in optical fibres, we investigate the impact of MGy dose levels on the mechanical properties of different single and multimode fibres. We compare the tensile test and two-point bending test results obtained by two different laboratories with commercially available optical fibres before and after irradiation up to 15 MGy. Our results show a significant strength reduction of about 50 % at high dose levels, relevant for particular applications in nuclear power facilities and in large nuclear physics experiments. This strength reduction seems to depend on both the coating materials and the test conditions, as suggested by the roughening of the outer glass surface of the optical fibre, observed with atomic force microscope (AFM) images.

The dynamic fatigue test is often preferred to the static fatigue test to measure stress corrosion parameters due to the short time required to conduct tests. The results can be interpreted using the power law or the exponential law for crack growth. However, the results are usually interpreted using the power law which can be analytically integrated in the dynamic fatigue form in contrast to the exponential law which cannot be integrated analytically. Nowadays, the two-point bend machine is used widely to carry out dynamic fatigue tests. Two loading modes are available for this machine: constant plate speed and constant stress rate. In the constant plate-speed mode the mobile plate moves with constant speed towards the other plate thus increasing the stress at the apex of the bent fibre in a non-linear profile. The constant stress-rate mode, which is the more advanced, requires that the mobile plate moves at a variable speed to maintain a constant rate of stress increase at the apex of the optical fibre. In this paper we examine dynamic fatigue tests on optical fibre in water at different temperature using both the constant stress-rate and the constant plate-speed loading-profiles. Then we analyze the results using the power law and the exponential law for crack growth. The parameters for stress corrosion are then used to predict static fatigue behaviour of the optical fibre and are compared with experimental results of static fatigue carried out in two-point bend under water.

Reliability of standard single mode silica optical fibre and hermetic coated fibre has been investigated through chemical exposure to hydrofluoric acid (HF) vapours into a hermetic closed disposal for different durations. Dynamic fatigue tests were implemented using a two-point bending testing device. Three series of samples subject to HF attack for variable times were compared. Standard fibres tested immediately after exposure show a broader distribution of fibre strength accompanied by the drastic decrease of the failure stress. Drying treated standard fibres prior to testing has also led to a broader distribution and a slight decrease of failure stress by comparison to as-received fibres. Drying in oven prior to mechanical measurement makes handling difficult and results in brittle fibres that exhibit much lower strength and broader distribution of failure stress. Polymer reacts with hydrogen fluoride, which induces viscosity changes, but it returns to solid state after thermal treatment. This is consistent with SEM observations. Same experiments have been implemented on the hermetic coated fibre. No significant change in the Weibull distribution and the mean fibre strength was observed after 6 days of chemical exposure to HF vapours. By comparison to standard commercial fibre, the hermetic coated fibre appeared extremely durable in harsh chemical conditions.

A comparative study among the Jones matrix analytical models with high-order PMD is presented. The models that make use of an exponential expansion arrested up to second order or consider the dispersion vector as a Taylor series expansion do not give good results in the approximation of high-order PMD effects, because of the nonlimited behavior with respect to frequency of the modulus of their dispersion vectors. On the other hand, the analytical model which describes the dispersion vector as rotating on a circumference in the Stokes space is found to be the most accurate. Moreover, it can be used to obtain an analytical expression of the pulse broadening, which is often chosen as a quality-system parameter.

"Qualification" of fiber optic components holds a very different meaning than it did ten years ago. In the past, qualification meant extensive prolonged testing and screening that led to a programmatic method of reliability assurance. For space flight programs today, the combination of using higher performance commercial technology, with shorter development schedules and tighter mission budgets makes long term testing and reliability characterization unfeasible. In many cases space flight missions will be using technology within years of its development and an example of this is fiber laser technology. Although the technology itself is not a new product the components that comprise a fiber laser system change frequently as processes and packaging changes occur. Once a process or the materials for manufacturing a component change, even the data that existed on its predecessor can no longer provide assurance on the newer version. In order to assure reliability during a space flight mission, the component engineer must understand the requirements of the space flight environment as well as the physics of failure of the components themselves. This can be incorporated into an efficient and effective testing plan that "qualifies" a component to specific criteria defined by the program given the mission requirements and the component limitations. This requires interaction at the very initial stages of design between the system design engineer, mechanical engineer, subsystem engineer and the component hardware engineer. Although this is the desired interaction what typically occurs is that the subsystem engineer asks the components or development engineers to meet difficult requirements without knowledge of the current industry situation or the lack of qualification data. This is then passed on to the vendor who can provide little help with such a harsh set of requirements due to high cost of testing for space flight environments. This presentation is designed to guide the engineers of design, development and components, and vendors of commercial components with how to make an efficient and effective qualification test plan with some basic generic information about many space flight requirements. Issues related to the physics of failure, acceptance criteria and lessons learned will also be discussed to assist with understanding how to approach a space flight mission in an ever changing commercial photonics industry.`

We discuss on-going reliability studies of micro-optical components and assemblies as conducted in the EU FP6 Network of Excellence on Micro-Optics "NEMO". We focus on three case studies including first biaxial fatigue testing of micro-optical components, second reliability testing and quality control of MEMS and third micro-interferometric tomography for measuring optical fibre refractive index changes. For each of these case studies we discuss the dedicated measurement and characterization methods as well as first results and the perspectives for future research.

The stresses in a microstructured optical fiber are determined in tension and in bending. A model for the failure process in porous structures with applications to weak microstructured optical fibers with large flaws is proposed. The model assumes that a continuous crack front splits on contact with a hole and then propagates such that the direction of the front in contact with the boundary of the hole is normal to it. Three-dimensional finite perturbation analysis of Bower and Ortiz1 is extended to model the interaction of cracks with a periodic array of holes. Crack propagation in the cross-section is examined using the modified finite perturbation method. Test cases are presented for the stress intensity factor distribution in elliptical cracks, and periodic perturbations in straight cracks. During crack front interaction, the front can split upon contact with the hole or an array of holes, and then travel around them.

North American deployments of FTTP architectures have been rapidly increasing. While the FTTP market is being driven by major telecommunications service providers, equipment suppliers have been scrambling to bring products to market that will ensure them a piece of this high-stakes market. In this invited presentation/paper, we propose to examine the technical requirements that are needed to support the new FTTP network with a host of new products that have been in development. To enable service providers select the best new products for FTTP deployment, product selection needs to be based on the analysis and testing of new products for performance and reliability, Telcordia, in its traditional role of telecommunications standards development, has been publishing generic requirements (GR) documents that have been used by suppliers, service providers and the industry at large. Product qualification programs based on the established performance and reliability requirements/standards have been designed to evaluate products to determine if they can 1) withstand the rigors of the outside plant deployment environment and perform for extended periods of time, 2) be upgradeable, and 3) craft friendly. The outside plant is a tough environment to live in. A product must perform under the extreme conditions of cold down -40°C (-40°F) and hot up to 46°C (115°F) with high humidity of 95%, rain, snow, sleet, vibration due to traffic, lightning, heating due to solar loads, high winds, ice, sand storms, and products are even tested to demonstrate if they can continue to operate in an earthquake, a wild fire and a shotgun blast. All FTTP products are not only expected to perform, but they must meet stringent optical performance criteria of low insertion loss and reflectance / return loss at a broad range of wavelengths from 1310, 1490, 1550 and 1625 nm. While the upstream (from the customer to the CO) voice and data transmission is currently planned over 1310-nm wavelength, the downstream (from the CO to the customer) voice and data transmission is offered over 1490 nm, the video (analog, digital and HDTV) transmission will be offered over 1550-nm wavelength, and the 1625-nm will be reserved for overhead, surveillance, and management functions. This paper will cover some of the new products that will be needed and the requirements that would apply. The FTTP deployments require the placement of a number of new products in the FTTP network from the CO to the customer premises. These new products are designed to be installed in an efficient manner with acceptable cost to the service provider in the outside plant and to perform the required functions. One such new product is an HFOC (Hardened Fiber Optic Connector). The HFOC products provide drop connections to customers from fiber distribution networks. They may be placed in pedestal closures, aerial and buried closures, or equipment located at a Fiber Distribution Hub (FDH) enclosure or optical network termination (ONT) unit near customer premises. Current versions of this HFOC product have been based on a well-known and widely used SC fiber optic connector. Simply described, it consists of an SC connector in a protective shell made of a polymeric (plastic) material, and it allows highly efficient connections between the distribution cables from the FDH (Fiber Distribution Hub) where optical signal on a feeder cable from the CO is split for transmission over distribution cables and drop cables in locations near customer premises. In addition to the description of new products, the paper will review the environmental, mechanical and optical test criteria. Attendees would benefit from the knowledge of products and requirements needed to support FTTP deployment.

In the bidirectional pumped Erbium Doped Fiber Amplifier (EDFA), we propose the new method with two Mutually Pumped Phase Conjugate Mirrors (MPPCMs) to couple the pump beam into the fiber. This method makes it possible to couple the pump beam into the propagation mode of the fiber without high precision adjustment by the characteristic of MPPCM. Additionally, high precision readjustment is not required when a LD, fiber or lens is exchanged due to failures. In our method, it is important to obtain high diffraction efficiency of MPPCM for high coupling efficiency between the pump beam and the fiber. Diffraction efficiency of MPPCM depends on the intensity ratio of two incident beam intensities inside the PRC. We analyze the coupling efficiency for the intensity ratio of two pump beams, and show the optimum intensity ratio of two pump beams. Then, we perform an experiment to couple the pump beam (Ar⁺ laser 514.5nm) to the fiber (multimode fiber of 62.5μm core diameter). In the experiment, coupling efficiency higher than 35% was confirmed. Moreover, in our method, the time to complete the coupling depends on the beam intensities in the early stage of the process. Therefore, we also propose the 4f imaging system to achieve a faster coupling at the early stage, and design the optical system to improve the time to complete the coupling in our method.

High power lasers emitting at 980 nm are essential for pumping sources of erbium-doped fiber amplifiers (EDFAs). These are used in longer distance telecommunications. Stability and reliability of the modules are two key characteristics. The present paper investigates 'sudden random failures' of double quantum-well 980 nm high power ridge waveguide lasers implemented in EDFAs. For the inspection of the external and internal status of the device we used optical spectrum modulation experiments, electroluminescence measurements, scanning electron microscopy and cathodoluminescence investigations. The localization of internal defects is the main point of this work. Two different 'sudden random failures' were found: catastrophical optical mirror damage (COMD) and internal dark line defect (DLD) formation.

All-optical wavelength conversion using cross-gain modulation in a semiconductor optical amplifier is one of the simplest and most common techniques to perform such operation. However, the finite gain recovery time of the amplifier causes severe distortion and pattern dependence at high bit-rates. The present work shows that it is possible to reduce the pattern dependence of the output converted signal using a fiber Bragg grating operating on its transmission edge. A wavelength converter using the non-linear effect of cross-gain modulation in a semiconductor optical amplifier can be assembled in the co-propagating and counter-propagating modes. The advantage of the counter-propagating mode is the possibility of an assembly without an optical filter in the output of the converter to filter the input signal, however this scheme introduces crosstalk in WDM systems, due to the residual facets reflectivity of the semiconductor optical amplifier. In this paper we analyze by simulation using commercial software, the improvement in the frequency response of a wavelength converter based on cross gain modulation in semiconductor optical amplifier in the counter-propagating mode using a fiber Bragg grating. The simulation results show that, with the fiber Bragg grating in the output of the converter, the pattern dependence of the converted signal is reduced. This paper also shows the advantages and disadvantages of the counter-propagating mode.

We examined the room temperature radiation-induced optical attenuation of silica-core, polarization-maintaining fibers with boron stress rods. The fibers were exposed to 55 MeV protons to equivalent doses between 100 krad and 1 Mrad at dose rates of 2 to 100 rad/s. Spectra from 1250-1725 nm were recorded during both exposure and ~2,800 h recovery. The spectral response over time indicates two separate populations of defects that affect loss. Explicit kinetic modeling indicates that the growth of the induced loss is consistent with a power law in dose rate, and recovery is consistent with low (1^st or 2^nd) order annealing with a distribution of activation energies and a single attempt frequency for each population. For predicting the radiation-induced loss in exposure conditions of much lower dose rate and much longer time, our theory and numerical simulations indicate that the best experiments for reducing risk in our extrapolations include higher temperature anneals, and, unavoidably, longer exposures at lower dose rate.

Stoichiometric defects in glasses play a critical role in determining its optical properties. Defect types in silica and germanosilicates are briefly reviewed. Passive components in fibers based on stoichiometric defects, such as Bragg and long period gratings have been developed and used extensively in high reliability applications. Approach to analyze thermally associated changes in these gratings over time is outlined. The applicability of the approach to other defect related phenomena such as hydrogen induced loss in optical fibers is also described.

The annealing properties of Type IA Bragg gratings are investigated and compared with Type I and Type IIA Bragg gratings. The transmission properties (mean and modulated wavelength components) of gratings held at predetermined temperatures are recorded from which decay characteristics are inferred. Our data show critical results concerning the high temperature stability of Type IA gratings, as they undergo a drastic initial decay at 100°C, with a consequent mean index change that is severely reduced at this temperature However, the modulated index change of IA gratings remains stable at lower annealing temperatures of 80°C, and the mean index change decays at a comparable rate to Type I gratings at 80°C. Extending this work to include the thermal decay of Type IA gratings inscribed under strain shows that the application of strain quite dramatically transforms the temperature characteristics of the Type IA grating, modifying the temperature coefficient and annealing curves, with the grating showing a remarkable improvement in high temperature stability, leading to a robust grating that can survive temperatures exceeding 180°C. Under conditions of inscription under strain it is found that the temperature coefficient increases, but is maintained at a value considerably different to the Type I grating. Therefore, the combination of Type I and IA (strained) gratings make it possible to decouple temperature and strain over larger temperature excursions.

Long period gratings have been inscribed in standard single mode fibre using a fs laser system, a fusion arc and a UV laser and a comparative study carried out of their thermal behaviour. The fs laser induced gratings can survive temperatures in excess of 800 °C, however the inscription process can induce considerable birefringence within the device. Annealing studies have been carried out showing that below 600 °C, all three grating types show a blue shift in their room temperature resonance wavelengths following cyclic heating, while above 600 °C, the UV and arc induced LPGs exhibit a red shift, with the fs LPG showing an even stronger blue shift. High temperature annealing is also shown to considerably reduce the birefringence induced by the fs inscription process.

Optical losses induced in fibers at 300^oC and in hydrogen atmosphere were studied. A non-linear dependence of hydrogen penetration through the carbon coating on hydrogen pressure was observed. It was demonstrated that carbon coating could not defend the fiber from hydrogen penetration for a long time period. At some time, the hydrogen presence in the fiber core resulted in high optical losses in all spectral range in the case of Ge-doped fibers. It was found that the short-wavelength loss edge (SWE) in a Ge-doped fiber co-doped with a small amount of phosphorus was significantly smaller than that in Ge-doped fibers without co-doping. Nevertheless, P-codoping effect did not decrease optical losses related with SWE completely.

Bandpass filters based on π-phase-shifted long-period fiber grating have been theoretically analyzed and experimentally fabricated by the electric-arc technique. Calculations and numerical simulations, based on coupled mode theory associated with the F-matrix method, have shown that the isolation of lateral rejected bands is maximum when the total length of the grating is optimised and the π-phase-shift inserted when the transmission at the desired resonance wavelength is -6.9dB. Two π-phase-shifts are introduced at optimised positions to obtain a large bandwidth of the badpass filter. We have fabricated the first bandpass filters that have lateral rejected bands isolation higher than 20 dB and bandpass filters with very large flat-top bandwidths (FWHM =19.5 nm) around 1538 nm peak, the fabricated filters are characterized by a very low insertion loss (<0.5 dB).

In this paper we report on investigations of some of the factors that have a bearing on the reliability and repeatability of polymer fibre Bragg gratings. The main issues discussed are the fibre preform composition, the fibre drawing conditions and the thermal history of the fibre grating.

Optical fibers with different protective coatings were abraded then submerged in 50°C water for twenty-eight days. The strength of the abraded and control fibers exposed to zero-stress aging was tracked over time with tensile strength testing. Although the abrasion test represented a severe model of fiber handling, no appreciable strength degradation was detected on the fiber before or after zero-stress aging.

Specialty optical fibers operating in harsh aerospace environments are typically exposed to high temperatures and elevated humidity. This calls for better performing protective coatings. Recently developed sol-gel derived inorganicorganic hybrid materials called hybrid glass offered improved protective performance as compared to standard dual polymer coated fibers [1]. In this paper we examine the effectiveness of online UV curing for the protective ability of hybrid glass coatings. For this purpose two types of UV-curable hybrid glass candidates representing two different concentrations of acrylate groups were applied online to silica fibers as single and dual coats. Samples of fibers were collected and subjected to dynamic fatigue testing by two-point bending. The stress corrosion parameter, n, as well as the strength of the fibers were determined. Both the strength and n were higher for fibers with two layers of coating as compared to single coatings even when the thickness of both one and two layer coatings was the same. This may be caused by the greater degree of cross linking of the inorganic component when the coating is exposed twice to the heat generated in the UV chamber. Coating materials with reduced acrylate group content had higher values of the fatigue parameter n but at the same time reduced strength.

The full characterisation of a fibre's sensitivity to high power damage is time consuming and expensive. The fibre's initial equilibrium temperature under bending is a practical metric that can be used to mitigate the risk of damage by keeping this temperature below that which causes accelerated ageing of the coating. Modelling of the temperature distribution can be used to filter fibre and coating designs before proceeding with more expensive experimental evaluation. The inclusion of stress terms that modify the refractive index in the BPM analysis of bend loss enables the bend loss to be modelled more accurately. This together with the appropriate thermal boundary conditions on the fibre surface substantially improves the accuracy of computing the temperature distribution within the coatings of a bent fibre.

The fast mode of optical discharge propagation in optical fibres was observed. In contrast to the known fibre fuse effect such optical discharge propagation is accompanied by fibre cracks and velocity reaches≈3km/s under the intensity 40W/ μm².

A fiber design is proposed that addresses bend loss, high power and handleability concerns for fibers deployed in high power devices and associated pigtails. If bending is tight enough to leak power from the core into the glass cladding, a coating with a sufficiently low index traps this potentially dangerous power in the cladding. The coating is also designed to keep cladding power from damaging downstream devices and terminations. Loss due to tight bends is minimized by use of a glass design with a small mode-field diameter. This glass design further suppresses the high power failure mode. Over the high power coating is a thick layer of a toughened polymer coating which provides a significant increase in mechanical protection over most commercial coatings.

We report the first experimental measurements on the spectral modification of Type IA fibre Bragg gratings, incorporated in an optical network, which result from the use of high-power, near infrared lasers. The fibre grating properties are modified in a controlled manner by exploiting the characteristics of the inherent 1400nm absorption band of the optical fibre, which grows in strength during the Type IA grating inscription. If the fibre network is illuminated with a high power laser, having an emission wavelength coincident with the absorption band, the Type IA centre wavelength and chirp can be modified. Furthermore, partial grating erasure is demonstrated. This has serious implications when using Type IA gratings in an optical network, as their spectrum can be modified using purely optical methods (no external heating source acts on the fibre), and to their long-term stability as the grating is shown to decay. Conversely, suitably stabilised gratings can be spectrally tailored, for tuning fibre lasers or edge filter modification in sensing applications, by purely optical means.

We report on high power issues related to the reliability of fibre Bragg gratings inscribed with an infrared femtosecond laser using the point-by-point writing method. Conventionally, fibre Bragg gratings have usually been written in fibres using ultraviolet light, either holographically or using a phase mask. Since the coating is highly absorbing in the UV, this process normally requires that the protective polymer coating is stripped prior to inscription, with the fibre then being recoated. This results in a time consuming fabrication process that, unless great care is taken, can lead to fibre strength degradation, due to the presence of surface damage. The recent development of FBG inscription using NIR femtosecond lasers has eliminated the requirement for the stripping of the coating. At the same time the ability to write gratings point-by-point offers the potential for great flexibility in the grating design. There is, however, a requirement for reliability testing of these gratings, particularly for use in telecommunications systems where high powers are increasingly being used in long-haul transmission systems making use of Raman amplification. We report on a study of such gratings which has revealed the presence of broad spectrum power losses. When high powers are used, even at wavelengths far removed from the Bragg condition, these losses produce an increase in the fibre temperature due to absorption in the coating. We have monitored this temperature rise using the wavelength shift in the grating itself. At power levels of a few watts, various temperature increases were experienced ranging from a few degrees up to the point where the buffer completely melts off the fibre at the grating site. Further investigations are currently under way to study the optical loss mechanisms in order to optimise the inscription mechanism and minimise such losses.

Five different multimode optical fibers have been coated with an antireflective coating to minimize transmission losses. The transmission, the stimulated Brillouin scattering (SBS) threshold and the laser-induced damage threshold (LIDT) were determined for the fibers. The measurements are performed at 1064 nm with 24 ns pulse duration. Fiber transmissions reach up to >99.5% for optimal laser beam coupling. A damage threshold of up to 125 J/cm² could be achieved. The fiber coatings were investigated using atomic force microscopy and scanning electron microscopy.

High availability tops the list of features desired for building a network. Various factors influencing path availability of optical networks with span restoration are investigated from the network design point of view. Network redundancy, number of backup routes, and dual span failure restorability can have important effects on path availability. A formulation to improve average path availability of a network by maximizing dual failure restorability is developed. We also introduce a practical method to optimize spare capacity and path availability of a network at the same time. A case study analyzes how much average dual-failure restorability can be improved in a long haul network with span restoration. Conclusions deduced from the computational and analytical results can help network planners to design a network with high performance and optimized cost and availability.

This paper reports simulation results of transmission performances after introduction of DFB laser diode parameters variations versus time extrapolated from accelerated tests. Simulations are performed using a system simulator to study the consequence of degradations of the laser diode on system performances (eye diagram, quality factor - Q and binary error rate - BER). The studied link consists in 4x2.5 Gbits/s WDM channels with direct modulation and equally spaced by 0,8 nm around the 1550 nm central wavelength. In this paper, only one channel is assumed to be degraded considering an only one activation energy. Simulation results clearly show that variation of basic parameters such as bias current or central wavelength induces a penalization of dynamic performances of the complete WDM link. Consequences on adjacent channels are pointed out underlying the relation between the variations of eye diagram parameters (height, noise, cross-talk, jitter) and the Q-factor decrease. Variations of optical spectrum density at the output of the demultiplexer are also analyzed showing penalties on the final cross-talk. Different degradation kinetics of aged laser diodes from a same batch have been also implemented to build the final distribution of Q-factor and BER after 25 years finally demonstrating the low impact of such variations. The strong interest of this approach is to evaluate the robustness of a dedicated-technology and to become a complementary tool of actual reliability-testing methods and physics of failure in the context of new reliability modeling approach. We have also highlighted the relevance of failure criteria established by actual qualification standards for high-rate optical telecommunication systems.

The restoration time in high capacity optical networks has to be kept as short as possible in order to avoid a huge loss of data. This paper discusses several methods to improve restoration time in optical networks and we propose mechanisms of implementing such inter-layer communication in order to decrease restoration time for a 10 Gigabit Ethernet based network.

The performance of a Subcarrier Multiplexing (SCM) optical fibre system using QPSK modulation is analysed in this paper. Our results will show that it is possible to increase the system bandwidth by controlling the input optical power. Various fibre dispersion values and subcarrier channel spacing are used in order to check the bandwidth increase proportional to the optical power. The transmission bandwidth was studied in terms of fibre dispersion and input optical power. The frequency response was measured and computed. Limitations imposed by nonlinear distortions mainly due to interplay between dispersion and self-phase modulation are verified as well. The analysis to the SCM_QPSK transmission system such as the subcarrier channel spacing, signal input power, available frequency bandwidth under the fibre specifications and system conditions operation will be explored in a specific application. It means applying this technique after setting the requirements necessary to the operation of an optical ground-wire (OPGW) already installed system. The results showed an increase of the transmission bandwidth as the optical power increases. For QPSK modulation, power penalties smaller than 1 dB were obtained only for channel spacing higher than 1.2 multiplied by the symbol rate. Experimental measurements obtained in the literature were used to validate our results. Eye opening and received eye diagrams will be evaluated in order to have a simpler receiver layout and make the entire system more reliable, since it will become more robust to error disturbance, maintenance is easier and system upgrades will be facilitated.

Optical networks carry an increasing amount of traffic due to the rapid growth of IP and multimedia services. Therefore the impact of network failures on this traffic and thus user services is growing fast. In addition some network services are heavily dependent upon the availability of communication resources. Consequently, network operators have to deal with the steadily growing availability requirement. Thus, survivability mechanisms need to be provided in the networks to meet the connection availability requirement. There are several protection schemes that can be applied to improve connection availability in the network. Shared Path Protection (SPP) scheme is selected in this paper due to its efficiency in resource utilization. In many works the SPP scheme has been studied to solve a single failure problem. However, in large networks the occurrence of multiple concurrent failures cannot be neglected [1]-[3]. In this respect we studied the SPP scheme for mesh optical transport networks with multiple failure scenario and developed connection availability model with multiple failure assumption instead of traditional single failure assumption. In this paper we present the analytical model for connection availability in SPP mesh network with multiple failure assumption. Our model is more general than the traditional model adopted for single failure assumption and also is more general than the work for two protection paths. We also developed a simulator to evaluate our analytical model. The results show that the connection unavailability obtained by simulations is very close to the theoretical value, which approve that our algorithm is accurate.

In this paper we analyze by simulation a measured amplified single channel 40 Gb/s communication system composed by standard fiber. Two different commercial simulation tools are used to perform the calculations. Experimental results were reproduced in such distinct simulation environments that allowed calibrating and predicting the system performance when new parameter settings are taken into evaluation. The simulation results indicate that at least 10 dB less power is required to achieve the same BER simply using an optimized receiver. That result enabled to have the same BER and also allowed removing the EDFA. Since one device such as an EDFA could be eliminated of the layout, with less optical power being required in the receiver, fiber spans as short as lengths that eliminate the dispersion compensation have been considered.

This paper discusses some novel strategies to tackle the difficulty problem of finding a good logical network topology with minimum traffic congestion. We apply our strategy on solving two typical topologies structures: the Mesh and the Self-Healing Rings. The typical strategies for solving the logical topology design for both structures are those based on the use of mixed-integer linear programming. However the literature shows that these approaches can be frustrating, time consuming and costly. As an alternative to these strategies, our approach combines the capability of meta-heuristics of finding good solutions in a very short computational time and provides the mixed-integer linear programming with good upperbounds in order to pruning great chunk of the searching space. In this work we show that our approach is promising as we are able to solve large problems in a reasonable amount of time for both type of topologies we studied.

Initial and radiation-induced optical loss spectra of multimode pure-silica-core holey fibers drawn at different regimes are analyzed and compared with those of a conventional POD-fiber with the same KU-1 silica in the core. It is shown that by filling the holes with H₂ gas during fiber drawing, it is possible to fully suppress the drawing-induced 630 nm absorption band and to lower the amplitude of the radiation-induced 610 nm absorption band. The results of an experiment are discussed in which H₂ gas was conducted through the holes of a multimode pure-silica-core holey fiber immediately in the process of its γ-irradiation. The dose evolution of the 610 nm absorption band and of the short-wavelength (≤ 550 nm) absorption associated with hydrogen incorporation into the glass network is analyzed. It is concluded that H₂ gas is efficient at suppressing the 610 nm band in pure-silica-core holey fibers, but can cause a loss increase in the short-wavelength region, in case its pressure in the holes is not sufficiently high.