Based on the increased interest for optical fibres development for the use in smart structures and sensors, this study has
aimed to investigate the chemical reliability of standard commercial epoxy-acrylate polymer coated fibres subjected to
aggressive chemical reagents in gaseous and liquid phase, such as acetylene, ammoniac, dimethyl sulfoxide. Multimode
optical fibre was exposed to gaseous reagents for different durations after prior vide exposure. Tensile testing results
were treated using Weibull statistics. A comparison of mean failure strength of as-aged fibres to the water influence for
similar exposure duration has revealed the highest sensitivity to dimethyl sulfoxide reagent.
The reliability and the expected lifetime of optical fibers used in telecommunication technologies are closely related to
the chemical environment action on the silica network. To ensure the long-term mechanical strength of the optical fibers,
a polymer coating was applied onto the fiber surface during fiber fabrication. This external coating is vital to ensure a
long fiber lifetime. Its protective action includes several functions, such as to protect glass fiber from any external
damage, to limit chemical attack, in particular that of water, and finally to ensure fatigue protection and bending
insensitivity. Since the mechanical strength of the fiber is controlled by its surface characteristics, we propose a new
method for increasing fiber strength.
Submitted to a mechanical stretching, fibers were plunged into hot water and aged for several days. Then, the fibers were
removed from the water and various weights were suspended on the fiber ends. Just before the fiber rupture, the fibers
were unloaded and subjected to dynamic tensile tests at different velocities.
Result analysis proved that the aging in hot water increased the fiber strength. The Weibull's diagram study shows a
bimodal dispersion of defects on the fiber surface and the important role of polymer coating.
Silica optical fibres that were developed for telecommunication networks extend their use for sensors and smart
structures. Their reliability and expected lifetime has appeared as a major concern. Series of experiments were
implemented in order to assess fibre behaviour in different environmental conditions, including chemical corrosion and
mechanical stress. Optical fibres were aged in water under controlled stress overlapping microwave energy for different
durations. Fibre samples were wound on different diameter mandrels applying consequently a non-uniform tensile,
respectively compression stress in function of the fibre's section. Different experimental combinations were
implemented in order to separate aging factor effects. Then, these aged / stretched fibres were dynamic tensile tested at
different strain rates and results were statistically treated using Weibull theory. In certain cases and testing conditions,
comparison with as received fibres has revealed strength increase with a generally mono-modal defect distribution on the
fibre surface. Base on previous and current results, the structural relaxation phenomenon at the silica cladding - polymer
coating interface might be evidenced.
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.
Four commercial single mode silica fibers were subjected to aging testing in hot water at different temperatures and durations. Static fatigue testing have showed an oscillating behaviour of fiber failure strength versus the aging duration, that may be explained through the structural relaxation phenomenon at the glass-polymer coating interface. For several aging durations, fibers appeared more resistant under static stress than the non-aged ones. The fiber strength measured dynamically, using a two point bending test, slightly decreased in the same aging conditions. Dynamic fatigue testing of as-aged fibers under permanent stress revealed an overall decrease of failure stress and a change of Weibull distribution towards a bi-modal dispersion. As-aged fibers presented a permanent curvature following aging treatment and drying.
Optical fibers are key components in telecommunication technologies. Apart from optical specifications, optical fibers are expected to keep most of their physical properties for 10 to 20 years in current operating conditions. The reliability and the expected lifetime of optical links are closely related to the action of the chemical environment on the silica network. However, the coating also contributes largely to the mechanical properties of the fibers.
The aim of this work was to study the strength and the mechanical behaviour of the silica optical fibers in an acid environment. A container with ammonium bifluoride acid salt was plunged into hot water at different temperatures (55° and 75°C). This emitted acid vapors which attacked the optical fibers for a period of 1 to 18 days. An aging study was performed on silica optical fibers with standard polyacrylate coating and with hermetic carbon coating. A dynamic two-point bending bench at different faceplate velocities (100, 200, 400 and 800 μm/s) was used. For comparison, the same dynamic measurements were also carried out on non-aged fibers.
After acid vapor condensation, salt crystal deposits on the fibers were displayed using an electron scanning microscope. These crystals became visible to the naked eye from the 7th day post exposure.