We designed face-centered cubic-structured (fcc) photonic crystals whose lattice parameters were tuned by varying the size of the constituent spherical silica particles in the range 100 to 520 nm. From wide-angle optical transmission investigations and Gaussian fitting of the absorbance spectra over UV-Vis-Near IR range, we found that in these crystals the Bragg wavelengths of the photonic band gaps (PBGs) corresponding to the reflected crystal planes linearly increase with the size of the spheres as expected. From this data, the average refractive index along the different crystal planes of the fcc structure was found to be in the 1.24 to 1.32 range. The Bragg wavelengths were tuned between 400 and 1100 nm. Thus, photonic crystals of the same structure can be designed to tune the Bragg wavelengths of PBGs by selecting the sphere size. These studies open up possibilities to design a new class of "smart" photonic crystals consisting of dielectric entities of sub-micron silica spheres with added functionality from magnetic or piezoelectric nanoparticles embedded in them.
The impact of silica glass structure on the transmission properties of Ge-doped single-mode optical fibers was studied. Test fibers with significantly different fictive temperatures (Tf) and residual stresses were drawn by varying cooling rate. Tensile or compressive residual stresses were achieved in core of the fibers. The results show that: (1) Both residual stress and Tf have an impact to the transmission properties, in particular, the stress in core. (2) A greater complexity was found in the relationship between transmission properties and glass structure than has been shown earlier. E.g. Rayleigh scattering was found to decrease and loss imperfection factor to increase with increasing Tf within one of the fiber series. Thus Tf can not alone be used to characterize the fiber glass structure. (3)Rayleigh scattering is dependent on both Tf and residual stress, in particular on core stress and probably on the structure of core glass. A relatively low Rayleigh scattering was found in fibers with Tf as high as 1600°C. (4) Zero dispersion- and cut-off wavelengths are modified by residual stress.
It is a general assumption that water itself, rather than impurities of water solutions, is dangerous for standard optical fibers. In this review paper, a summary of the results on water test conditions, made by COST 246 Action, is given, and the factors affecting the test results of strength and fatigue tests, are discussed. A fiber may have very different strength degradation in water depending on the chemical conditions, such as, ion concentration of the water, test vessel material, temperature etc.
Short summary of the achievements and conclusions of the European research action COST 246, titled Materials and Reliability of Passive Optical Components and Fiber Amplifiers in Telecommunications Networks, which was current during 1993 - 1998, is given.
In this report, we present an experimental analysis of the mechanical behavior of fused silica standard telecommunication fibers aged in hot air and hot filling compound. Our measurements at standard room temperature conditions after the aging treatments indicated tensile strength increases of up to 5% at 85 degrees Celsius and 15% in filling compound after one- to six-month aging. The dynamic fatigue for the fibers aged in the filling compound also improved (n-values from 17 - 20 to 25 - 30) in parallel with the fiber strength while the fiber static fatigue tests gave large n-value increases from 30 to 140. In order to examine the effects of the aging treatments on the fiber coatings, we used dynamic mechanical analysis to measure the coating mechanical properties, storage modulus E' and loss tangent tan (delta) . In general, we have found that aging in hot air and in the filling compound results in a significant decrease in E' and increase in tan (delta) , thereby suggesting an aging-related increase in the capacity of the coating to absorb substantial amounts of mechanical energy. A qualitative theoretical analysis of the coating contribution to the fiber crack growth and mechanical behavior in conjunction with our experimental results suggests that the coatings' ability to absorb more mechanical energy during aging contributes to increased fiber strength and improved fatigue behavior. Thus, our results to date provide the first experimental evidence that a fiber coating can stabilize cracks on fused silica surfaces and contribute in a significant way to fiber mechanical behavior.
The effects of glass preparation on the surface corrosion of fused silica optical fibers was studied by aging different fibers in both deionized water and tap water at 80-85 degrees C for several months and then analyzing the surface morphology of the samples using atomic force and scanning electron microscopies. We observed that surface corrosion, which causes strength degradation, is related to preparation defects in the glass, these include the existence of glass particles and layers, the presence of impurities and point defects, and in general all locations at which the bond strength is less than that of the Si- O bonds of silica. We found fibers whose surface did not become rough, despite the presence of a corrosive coating. we also find fibers whose surface roughness remained constant during aging in water, due at least in part to the protection provided by the coating. These findings imply that the effects of the glass preparation on the surface corrosion can be minimized through careful attention to the glass and to the fiber manufacturing processes.
KEYWORDS: Scanning electron microscopy, Glasses, Corrosion, Atomic force microscopy, Electron microscopes, Atomic force microscope, Single mode fibers, Manufacturing, Fiber coatings, Surface roughness
In this work, we studied aged fibers using several different techniques: dynamic tensile testing, two-point bending, an AFM, and a scanning electron microscope (SEM). In particular, we sought to identify the mechanical causes of the low fiber strengths measured after nine months of aging in 80 degree(s)C water. By using a SEM to look at the broken ends and at the glass surface close to the breaks with the lowest failure stress, we gathered new information about the condition of the glass surface of the aged fibers.
The deployment of fiber in the subscriber loop will require that an optical fiber network maintain
the highest possible level of reliability over time, despite being subjected to extremes of
temperature, humidity, and other environmental and mechanical stresses imposed on the outside
plant. At the same time, both the initial cost and the ongoing maintenance expenses for loop
equipment must be kept low.
Fiber in the Loop (FITL) applications will entail increased fiber handling. Cable lengths will be
shorter, and fiber counts higher, than has been the case so far in long-distance applications. There
will also be more cable sheath openings per unit length of cable and/or fiber, as well as more
splicing and connectorization. It may become a common practice that a customer is connected to a
cable installed many years earlier. In subscriber loops, cables and fibers will be installed in harsher
and more varying environments. Fibers will be exposed to higher humidity and temperature,
particularly in splice boxes mounted on building walls, in pedestal cabinets, and in other similar
enclosures. Corrosive gases and/or liquids may also be present at some locations and will adversely
affect the fibers. The combination of increased handling, greater exposure, and more stressful
environments may give rise to a need for new, more stringent requirements for fiber mechanical
reliability. These can include increaSed fiber strength, increased aging resistance, and increased
fatigue resistance.
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