Diffusion of moisture through optical fiber coatings

The strength of polymer-coated fused silica optical fiber is dependent on the ambient moisture because of stress corrosion. The diffusion rate of water vapor through the polymer coating can be estimated by monitoring the strength as a function of time after suddenly changing the ambient humidity. Not only is this technique a new way of sensing humidity, but it also allows estimation of the time needed for the coated fiber to equilibrate with its environment. A comparison has been made between the diffusion coefficients measured in this way and by monitoring the weight of free-standing polymer films as a function of time. Fickian diffusion has been assumed and is justified by the good agreement between the experiment and theory. The diffusion of water vapor both into and out of various polymers was investigated     

On the method for determining the true strength of inorganic glasses

The possibility of determining the true structural strength of glass by bending of glass fibers with a defect-free surface is considered. Two methods are compared, viz., the method of transverse three-point bending in which the breaking stress (strength) is determined, and the method of two-point bending in which the breaking strain is determined. In the latter case, the dependence of the elastic modulus on strain is required for determining the breaking stress (strength). The strength measured in three-point bending is compared with the strength calculated from the breaking strain measured in two-point bending. It is shown that the measurements based on these two methods give close values of strength for defect-free silica fibers used as optical waveguides. The observed difference of ～12% in the values of strength is explained by the difference in the loading rates obtained using these two methods. The advantages and disadvantages of these two techniques are analyzed.     

Strength and fatigue of silica optical fibers

After a brief review of early lightguide work, the authors assess advances since the mid-1970s. They note important work on strength distributions and procedures for improving strength. This is followed by a discussion of long-length strength, prooftesting and splicing. Flaw character is studied along with strength degradation, fatigue limits, aging and fatigue, and hermetic coatings     

Some examples of H to g transformations as applied to Fe3+ EPR in glass

In this paper we show some examples of transforming an Fe³⁺ EPR line shape in H into a probability density in g. We find that the classical g = 4.3 line in glass, though quite pronounced in the derivative spectra in H, is less striking in g. We also find that there are substantial contributions at g = 2 and g = 1 to the total g density distribution.     

Three‐Phonon and Four‐Phonon Interaction Processes in a Pair‐Condensed Fermi Gas

We study the interactions among phonons and the phonon lifetime in a pair‐condensed Fermi gas in the BEC‐BCS crossover in the collisionless regime. To compute the phonon‐phonon coupling amplitudes we use a microscopic model based on a generalized BCS Ansatz including moving pairs, which allows for a systematic expansion around the mean field BCS approximation of the ground state. We show that the quantum hydrodynamic expression of the amplitudes obtained by Landau and Khalatnikov apply only on the energy shell, that is for resonant processes that conserve energy. The microscopic model yields the same excitation spectrum as the Random Phase Approximation, with a linear (phononic) start and a concavity at low wave number that changes from upwards to downwards in the BEC‐BCS crossover. When the concavity of the dispersion relation is upwards at low wave number, the leading damping mechanism at low temperature is the Beliaev‐Landau process 2 phonons ? 1 phonon while, when the concavity is downwards, it is the Landau‐Khalatnikov process 2 phonons ? 2 phonons. In both cases, by rescaling the wave vectors to absorb the dependence on the interaction strength, we obtain a universal formula for the damping rate. This universal formula corrects and extends the original analytic results of Landau and Khalatnikov [ZhETF 19 , 637 (1949)] for the 2?2 processes in the downward concavity case. In the upward concavity case, for the Beliaev 1? 2 process for the unitary gas at zero temperature, we calculate the damping rate of an excitation with wave number q including the first correction proportional to q ⁷ to the q ⁵ hydrodynamic prediction, which was never done before in a systematic way.     

The fatigue of high-strength fused silica optical fibers in low humidity

The strength and dynamic fatigue of UV-acrylate coated silica optical fibers were measured as a function of relative humidity in the range ∼0.025-13% at 25 °C. The degradation kinetics of silica in low humidities was investigated and it was found that the reaction order was approximately first-order with respect to humidity. In our previous work, a second-order reaction was found in the humidity range 20-95% RH at 25 °C and the process for obtaining this reaction order was found to be independent of the mathematical form of the kinetic models used. The change in reaction order observed here verifies some earlier results based on the power law which implied a change in the reaction order from ∼2 (15-100% RH) to ∼1 at low humidity (<0.01%).     

Diffusion of moisture through fatigue- and aging-resistant polymer coatings on lightguide fibers

In previous work the diffusion rate of water vapor through the polymer coating on optical fiber was estimated by monitoring the strength as a function of time after suddenly changing the ambient humidity. This technique is used here to measure the diffusion of moisture both into and out of two novel fiber coatings. The first specimen is a dual-coated fiber with silica particles added to its secondary coating. It is shown that the improvement in this fiber's reliability is not due to the silica particles adsorbing/absorbing the moisture. The second fiber, coated with a fluorinated polymer, was designed to have higher fatigue resistance as a result of having a lower permeability to moisture. It is found that even though this fiber had higher than normal resistance to fatigue, the diffusion of moisture through this coating was not substantially different than through typical coatings used on fibers for telecommunications applications.     

Fibre splices with `perfect fibre? strengths of 5.5 GPa, v<0.01

Splices of single-mode fused silica fibre having strengths equivalent to that of the as-drawn fibre of ~800 ksi (5.5 GPa) with a coefficient of variation v of <0.01 are produced by fusion splicing with an H2-Cl2-O2 flame. These results demonstrate that fused silica fibre can be reheated to fusion temperatures and retain original high strength. The results are statistically analysed with respect to variations in breaking load, fibre and splice diameter, and relative humidity.