Analysis of thermal decay and prediction of operational lifetime for a type I boron-germanium codoped Fiber Bragg grating

Abstract

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 change in the grating characteristic 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.

An Improved Metal-Packaged Strain Sensor Based on A Regenerated Fiber Bragg Grating in Hydrogen-Loaded Boron–Germanium Co-Doped Photosensitive Fiber for High-Temperature Applications

“…The step of isothermal annealing at a temperature of 500 °C is zoomed. In this step, as the reflection peak power of the seed FBG fast decreases to the inflection point of complete erasure, the Bragg wavelength is abruptly shifted to shorter wavelengths, which indicates a strong decrease in both the refractive index modulation and average index change at this high temperature, and is typical behavior of thermal decay for a normal type-I FBG in PS1250/1500 fiber [36]. As the reflection peak power of the RFBG increases from the inflection point, its Bragg wavelength is much longer than that of its seed grating, consistent with the similar behavior reported in [37], which may be explained by the RFBG formed with changes (such as stress) at the core-cladding interface.…”

Characterisation of a polymer-coated fibre Bragg grating sensor for relative humidity sensing

“…The gratings were annealed for more than 7 h at 200 • C to stabilise the performance of the device [16]. Prior to the polymer deposition, the gratings were cleaved at one end to facilitate the use of the dip coating technique which was found to be most effective for this research.…”

Process monitoring of fibre reinforced composites using a multi-measurand fibre-optic sensor

“…Thermal annealing of type-I Ge-B co-doped fibre gratings is said to lead to a negative shift in the Bragg wavelength accompanied by a drop in the reflectivity. This has been attributed to the decay of the grating structure [37,38]. The temperature sensitivities of FBGs at 1552.3 nm, determined using the FiberPro interrogation unit, during the 1st and 2nd heat/cool cycles for the reference and coated FBGs were in the range of 9.7-9.9 pm K −1 respectively by considering a linear fit.…”