Characteristics of potential fibre Bragg grating sensor-based devices at elevated temperatures

Abstract

Fibre Bragg gratings (FBGs) of type I and IIA were fabricated in Ge-doped and B-Ge co-doped fibres using a 248 nm excimer laser and their performance characteristics were tested and compared with those of a chemical composition grating (CCG), written in a fluorine-germanium doped fibre, over a wide range of temperatures. Long-term testing (more than 600 h) involving a series of step-wise incremental temperature changes shows for the first time the potential of FBGs for high temperature measurement applications (up to and beyond 1100 • C), this depending on the type of FBG involved and the material and composition of the substrate fibre (the CCG was observed to be the most durable at very high temperatures). These gratings are likely to be useful for the simultaneous measurement of strain and temperature over these higher temperature ranges.

Thermal Evaluation of Fiber Bragg Gratings at Extreme Temperatures

“…While at 750°C, the original FBG exhibited a decrease in the Bragg wavelength of about 0.06nm. This initial shift to a shorter wavelength, also seen by Pal et al [2] and Brambilla [9], occurred through the With the formation of the new O-CCGs the power response began to increase as seen in Fig. 2 with the signal strength increasing each time the O-CCG was heated to 750°C.…”

“…However we saw a trend of shifting to longer wavelengths at high temperatures whereas he indicated a shift to shorter wavelength [2].…”

“…With the growing interest to use FBGs as temperature sensors in aerospace systems, the need to understand the performance and long term survivability of commercially available high temperature FBGs, up to 1000°C, has developed [1,2,3]. The survivability of FBGs up to and above 1000°C has generated interest [4,5], but their per-formance and long term survivability at these temperatures is not well published.…”

Bragg Grating-Based Fiber-Optic Laser Probe for Temperature Sensing

“…The first was Ge-doped fiber (from Nufern, Australia), into which was written the normal Bragg grating RB , because of the long lifetime and high stability of gratings in this fiber at elevated temperatures [6]. Using the second B-Ge codoped fiber (from Fibercore Ltd., U.K.), the chirped Bragg reflector RB was written, because of its higher photosensitivity.…”

“…From the characteristics of both the gratings and previous work on high-temperature grating fabrication [6], the upper limit of the measurement range of a system like this is expected to be no higher than 500 C, in order to allow a realistic lifetime for the probe before the grating "washes out." The repeatability of the measurement with the probe is 1.7 C, considering the linear graph fitting calibration characteristic shown in Fig.…”