The effect of annealing cycle on regeneration efficiency was investigated through isothermal treatments between 700 and 1000°C. We determined an inverse relationship between the recovery rate of the peak reflectivity and temperature. A regeneration efficiency of 85.2% and long-term stability at 1000°C for 500 hours were achieved via a slow regeneration process. Thermal sensors developed by isothermal regeneration were determined to be reliable up to 1000°C (±2 °C). Experimental findings suggest the involvement of both diffusion related phenomena and stress variation through densification of the fiber core in type-I FBG during the thermal regeneration process.

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Tubular hollow core fibers with low attenuation have great potential for different optical applications. Here we numerically investigate designs with a tailored jacket tube showing a significant confinement loss improvement of 27%-66% over a wide band from 1100 to 2000 nm.

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