Geophysical applications of optical fibers for distributed temperature, strain, and acoustic sensing challenges their reliability due to harsh environmental conditions. Which may include high temperature, pressure, presence of hot steam, hydrogen, and other aggressive chemicals. Robustness of silica-based optical fibers is primarily governed by the thermal and environmental stability of their polymer coatings. Among different types of coatings, polyimide materials exhibit favorable properties, such as durability at elevated temperatures, protection against solvents, and long-term mechanical reliability. In this work we investigate optical fibers employed with a novel polyimide coating. Extensive environmental testing was performed, comparing fibers with a standard and the novel coating. Fiber samples were aged in dry air (up to 380 °C), high temperature/pressure water, paraffin oil, crude oil, hydrogen scavenging cable gel and isopropyl alcohol (all up to 300 °C/2000 psi). Mechanical strength of the aged fibers was used as a measure of their performance at harsh conditions. In addition, we studied an adhesion that develops at elevated temperatures between the fibers and a stainlesssteel tube interior. Thermal stability of the polyimides was also evaluated via thermogravimetric analysis. Based on the obtained results, the novel polyimide coating shows a 35 – 38 °C improvement over the standard coating. The findings indicate the superiority of the new coating, which should extend the useful temperature range for this class of optical fibers.
Sterilization of medical equipment using e-beam or gamma radiation produces high sterility assurance but may lead to alterations in materials being treated. Thus, color centers developed in optical fibers result in added attenuation. In this work a series of specialty single-mode (SM) and multimode (MM) optical fibers (13 in total) were exposed to gamma and e-beam sterilization doses of 32 kGy, and the radiation-induced attenuation was investigated. The optical fibers selected for the study had different core chemical compositions, including pure silica and also SiO2 doped with Ge, F, P and Al. The fibers also differed in the clad diameters (80 and 125 μm), numerical aperture (0.1 – 0.21), coating types (carbon, acrylate, polyimide) and the cutoff wavelength (SM fibers only, 930 – 1470 nm). Effects of all these features on the radiation-induced attenuation were analyzed primarily in the framework of medical applications. The radiation-induced optical losses can be moderated by subsequent thermal treatment of the fibers, and such option was also investigated. Our results showed that while the radiation-induced losses may be high (102 – 104 dB/km), sterilization using e-beam and gamma radiation can be acceptable for many medical applications that deploy 3 m or less fiber lengths. After gamma or e-beam sterilization, 3 meters length of SM fibers with pure SiO2 and Ge doped core transmit >98% of optical power at 1550 and 1310 nm. In contrast, similar length of SM fibers with P and Al doped cores exhibit very low transmission and cannot be used after ionizing sterilization. Among the MM fiber, F-doped core fibers display much higher transmission than Ge-core fibers, especially at 850 nm. The clad diameter, coating type and bend insensitive features in the refractive index profile did not show much effect on the radiation-induced loss. While gamma and e-beam radiation caused similar changes in the attenuation spectra, gamma radiation caused ~25% higher loss increase than e-beam at the same 32 kGy dose. Since our data showed that postradiation annealing at 100°C for 24 hours results in only ~30% recovery of the radiation induced loss, it may not be practical to implement such annealing scheme for medical applications.
We have demonstrated that fiber Bragg gratings can be written through the carbon layer of carbon-coated optical fibers having different coating thicknesses. Specifically, grating index modulation amplitudes of ~2.5x10-5 and 0.52x10-5 were obtained in optical fibers having carbon layers 29 nm and 56 nm thick, respectively, without any extra photosensitization of the fibers. Subsequent experimental results showed that the carbon coatings in the grating areas didn’t change their hermetic properties. Finally, we describe the advantages of these gratings and their potential applications in fiber optic sensing.
Optical fibers and terminations were subjected to different sterilization techniques, including multiple
autoclaving and treatments with peracetic acid, E-beam and UV radiation. Effects of different sterilization
techniques on key optical and mechanical properties of the fibers and the terminations were revealed. The
primary attention was given to behavior of the coatings on the fibers and adhesives used in the terminations
in harsh sterilization environments. The optical fibers with following four coating/buffer types were
investigated: (i) dual acrylate, (ii) polyimide, (iii) silicone/PEEK and (iv) fluoroacrylate hard cladding/ETFE.
Optical fibers with different types of polymer coatings were exposed to three sterilization conditions: multiple autoclaving, treatment with ethylene oxide and treatment with gamma rays. Effects of different sterilization techniques on key optical and mechanical properties of the fibers are reported. The primary attention is given to behavior of the coatings in harsh sterilization environments. The following four coating/buffer types were investigated: (i) dual acrylate, (ii) polyimide, (iii) silicone/PEEK and (iv) fluoroacrylate hard cladding/ETFE.
Key properties of polyimide-coated optical fibers, unaged and exposed to various harsh environments, were investigated.
The main intent was to model extreme conditions that can be encountered in medical applications of the fibers. A fiber
designed by OFS showed good strength and was able to withstand exposure to extreme heat and humidity, multiple
autoclave cycles, extended water soak and immersion in organic solvents. Similar fibers offered by other suppliers
displayed shortcomings in some of the tested properties.
As a continuation of our earlier study at 2.1 μm wavelength, we have investigated the laser damage to
several types of step-index, large core (1500 μm) silica fibers at two new wavelengths by high power long
pulsed Nd:YAG (1064 nm) and Alexandrite (755 nm) lasers. It was observed that fibers with different
designs showed a significant difference in performance at these wavelengths. We will also report a
correlation of damage to the fibers between the two laser wavelengths. The performance analyses of
different fiber types under the given test conditions will enable optimization of fiber design for specific
applications.
Silica optical fibers are being increasingly used for delivering laser power in various medical
applications. Damage to the optical fiber caused by the high laser power level and tight bend of the
fiber in these applications poses a serious concern. In this study, we examined the damage of step
index multimode fibers transmitting Ho:YAG laser power up to 100 W at wavelength of 2140 nm
when bent to a diameter down to 5 mm. The performance of different types of fibers was compared
and other relevant issues were discussed.
A 980/1600 Wavelength Division Multiplexing (WDM) fiber coupler is a critical component of an L-band (1580 nm to 1620 nm wavelength region) Erbium Doped Fiber Amplifier (EDFA), and the application in the L-band requires low optical loss at 980 nm and 1600 nm for the single mode fiber used in making the coupler. Common single mode fiber, designed for use at 980 nm, would usually have a significantly higher optical loss at these wavelengths. Therefore, a new design may be required. In this paper, we describe our work in fiber design to meet the new requirements and discuss relevant issues, especially fiber attenuation and bend loss performance.
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.
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