title: Ultrahigh-Temperature Regeneration of Long Period Gratings (LPGs) in Boron-Codoped Germanosilicate Optical Fibre.
abstract: The regeneration of UV-written long period gratings (LPG) in boron-codoped germanosilicate "W" fibre is demonstrated and studied. They survive temperatures over 1000 °C. Compared with regenerated FBGs fabricated in the same type of fibre, the evolution curves of LPGs during regeneration and post-annealing reveal even more detail of glass relaxation. Piece-wise temperature dependence is observed, indicating the onset of a phase transition of glass in the core and inner cladding at ~500 °C and ~250 °C, and the melting of inner cladding between 860 °C and 900 °C. An asymmetric spectral response with increasing and decreasing annealing temperature points to the complex process dependent material system response. Resonant wavelength tuning by adjusting the dwell temperature at which regeneration is undertaken is demonstrated, showing a shorter resonant wavelength and shorter time for stabilisation with higher dwell temperatures. All the regenerated LPGs are nearly strain-insensitive and cannot be tuned by applying loads during annealing as done for regenerated FBGs.
authors: interdisciplinary Photonics Laboratories (iPL), School of Chemistry, The University of Sydney, Sydney NSW 2006, Australia. liusenanbei@gmail.com.|College of Optoelectronic Science and Technology, National University of Defense Technology, Changsha 410073, China. liusenanbei@gmail.com.
authors: Wen
authors: W
authors: Liu
authors: interdisciplinary Photonics Laboratories (iPL), School of Chemistry, The University of Sydney, Sydney NSW 2006, Australia. kevin.cook@sydney.edu.au.
authors: Kevin
authors: K
authors: Cook
authors: interdisciplinary Photonics Laboratories (iPL), School of Chemistry, The University of Sydney, Sydney NSW 2006, Australia. john.canning@sydney.edu.au.
authors: John
authors: J
authors: Canning
keywords: fibre optic sensors; glass relaxation; long period gratings; melting temperature; regenerated gratings; strain sensitivity; temperature dependence; transition temperature