Fluorescence-based measurement schemes using doped fiber: theoretical analysis and experimental validation

Fluorescence-based sensing and measurement schemes are widely used, for example, using doped "communications" fiber. The underlying physical principle exploited in these measurement systems is the thermalization which occurs between closely-spaced excited ionic energy levels when the levels are populated using an appropriate excitation source, usually an LED or LD. The two schemes compared in this paper (fluorescence lifetime (FL) and fluorescence intensity ratioing (FIR)) exploit very different aspects of the resultant fluorescence decay from these levels. Both have the major advantage of being independent of possible fluctuations of the excitation source, which is very important for robust measurements and the understanding of the physical processes. Fluorescence lifetime (FL) based sensing an analysis of the which enables the fluorescence lifetime to be determined. The fluorescence intensity ratio (FIR) in rare-earth-doped optical materials (particularly fibers) uses fluorescence from two closely-spaced levels to a common final state which is monitored, and the ratio of the two emission intensities is calculated, resulting in a temperature-dependent quantity. These approaches are discussed and compared.