Fibre length-dependent fluorescence spectral characteristics in high erbium concentration fibres for the optimization of FBG-based fibre sensor systems

This paper reports the behavioural characteristics of the fluorescence spectrum in high concentration 5000 ppm erbium-doped fibre (EDF), as a function of the EDF length, showing their potential for optical sensor applications to increase the potential number of multiplexed 'all fibre' sensors on a single channel. Experiments were conducted to analyze the fluorescence peak wavelength shift, the bandwidth and output power at a convenient fixed low pump power of 37 mW, using excitation from two different laser diodes wavelengths, at 980 and 1480 nm. It was found that the fibre length of the high concentration EDF has a direct effect on the fluorescence peak shift. The fluorescence spectrum tends to show different spectral profiles with its maximum position shifting towards longer wavelengths as the length of the EDF increases, with a bandwidth at full width half maximum (FWHM) covering portions of the C-, L-, and U-band. It has also been shown that pumping with the 980 nm LD contributes to a higher fluorescence shift compared to the 1480 nm LD, at the expense of output power. The use of the fluorescence peak shift is important in the design and optimization of efficient fibre Bragg grating (FBG)-based optical fibre and fibre laser-based sensor systems.