Predicting thermal stability of fibre Bragg gratings – isothermal annealing within isochronal annealing (original) (raw)
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Journal of Lightwave Technology, 2004
Accelerated-aging studies of chirped Bragg gratings written in deuterium-loaded germano-silicate fibers were carried out using isothermal and continuous isochronal anneal methods. The master aging curve obtained from the isothermal decay is explained using the Arrhenius-rate-model-based equation. An empirical polynomial function was used to fit the continuous isochronal anneal data. The estimated attempt frequency () values from the two anneal methods were found to agree well within error. Further, the model-based calculations were found to predict postanneal long-term behavior of the gratings extremely well. Implications of the two anneal methods to accurately predict the thermal stability of chirped fiber Bragg gratings are discussed in light of rapid and reliable qualification of different types of gratings written in different fibers. Index Terms-Chirped fiber Bragg gratings (CFBGs), isochronal anneal, isothermal anneal, long-term reliability, thermal stability. Nirmal K. Viswanathan, photograph and biography not available at the time of publication.
Reliability of Optical Fiber Components, Devices, Systems, and Networks III, 2006
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 180ºC. 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.
Applied Optics, 2000
We compare the results of thermally induced isochronal and isothermal decays of fiber Bragg gratings written through cw exposure of an unloaded germanosilicate fiber. We show that isochronal step decays can be used to predict isothermal decays, provided that some corrections are carried out to take into account a reversible change in grating reflectivity induced by the increase of the fiber temperature. The isochronal accelerated-aging method enables one to sample most of the initial distribution of trapped site energies in a fairly short time. Taking advantage of this property of the method, we show that the initial distribution for a weak grating is similar to those for stronger gratings. The consequences of this observation are discussed within the framework of the various reaction pathway model.
Applied Optics, 2003
The thermal decay of a type I fiber Bragg grating written at 248 nm in boron-germanium codoped silica fiber was examined in terms of its reflectivity and Bragg wavelength change. In addition to the decay in reflectivity, which was observed, a shift in Bragg wavelength over the temperature range considered was seen. A mechanism for the decay in the reflectivity was developed and modeled according to a power law, and the results were compared with those from the aging curve approach. The wavelength shift was simulated by modification of the power law, which was also found to fit well to the experimental data. Temperature-induced reversible and irreversible changes in the grating characteristics were observed and considered to be a means to predict the working lifetime of the grating at comparatively low temperatures. Accelerated aging was also reviewed and compared in terms of reflectivity and Bragg wavelength shift. It was shown that the temperature-induced irreversible shift in the Bragg wavelengths could not be predicted by use of the isothermal decay of the refractive-index modulation. The results were discussed within the framework of the current theoretical approaches for predicting the stability of gratings of this type.
Thermal behavior of Bragg gratings formed in germanosilicate fiber
2003
In this contribution we compare the thermal stability of type I and type IIa gratings written in germanosilicate fibers. We study and compare their central wavelengths drifts and variations of the maximum reflectivity with temperature. Also, two other important factors, the bandwidth and group delay characteristics are characterized, compared, and the differences justified, based on the gratings physical structure.
Fibre Bragg Gratings, towards a Better Thermal Stability at High Temperatures
Physics Procedia, 2015
Regenerated fibre Bragg gratings (RFBG) are obtained by heating an original seed grating until its reflection practically vanishes, which is followed by the growth of a new reflection band. Advantages of RFBG for sensing purposes are the longer lifetime and higher thermal stability at higher temperatures, as they have been observed to survive temperatures in the range 1300-1500 °C. The thermal stability of the RFBG permits several applications not attained by standard Bragg gratings.
Thermal decay characteristics of strong fiber Bragg gratings showing high-temperature sustainability
Journal of the Optical Society of America B, 2007
Strong fiber Bragg gratings (FBGs) with high-temperature sustainability were fabricated by writing the gratings into several specially developed photosensitive fibers. The thermal decay characteristics of these gratings were investigated over a temperature range from room temperature to 950°C. A cation-hopping model is presented to account for the obvious differences between the FBGs in terms of their thermal properties. A related cation-oriented trap distribution model is also used to simulate the decay properties of the gratings during high-temperature annealing and is found to yield a good fit to the experimental data. An accurate operating lifetime of these specially fabricated gratings can be predicted by using the cation-oriented trap distribution simulation.
Thermal Stability of Bragg Gratings Written in N-Doped- Silica-Core Fibers
AbstTact: The results of thermal tests of high-temperature Bragg gratings written in a nitrogen-doped-silica-core fiber are preented. The gratings were produced by the conventional teaique using an ArF excimer laser and a phase mask at various exposure regime: show that they can withstand heating up to 900•‹C. The possible physical mechanisms responsible for thermal decay of the gratings are analyzed. Based on these results, the grating written in this type of fibers is potential to be integrated in fiber sensor system, in order to develop a high temperature sensor.
A study of regenerated gratings produced in germanosilicate fibers by high temperature annealing
Optics Express, 2011
In light of recent proposals linking structural change and stresses within regenerated gratings, the details of regeneration of a seed Type-I Bragg grating written in H 2 loaded germanosilicate fiber annealed at high temperatures (~900°C) are systematically explored. In particular, the influence of the strength of the grating, the effect of GeO 2 doping concentration and the annealing conditions on regeneration are studied. We show that the role of dopants such as Ge and F contribute nothing to the regeneration, consistent with previous results. Rather, they may potentially be detrimental. Strongest regenerated gratings with R ~35% from a 5mm seed grating could be obtained in fibres with the lowest GeO 2 concentrations such as standard telecommunications-compatible grade fibre.
Thermal Evaluation of Fiber Bragg Gratings at Extreme Temperatures
43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005
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