Influence length of single-beam propagation in doped glass and polymer optical fibres

For characterisation of doped optical fibres (DOFs) based on single-beam propagation, one requires a maximum DOF length along which a signal power can propagate. In this work we have solved the rate equation for the single-beam propagation in both lossy and lossless DOFs, introduced an influence length as a maximum propagation length and then determined it analytically. With the analytical results obtained, the main regularities for the influence length have been simulated for the glass optical fibres doped with Ge/Al/Er operating at arbitrary wavelengths under lossless and lossy conditions. Also, the influence length has been determined for some kinds of co-dopants present in both polymer and glass optical fibres. The influence length thus defined may be useful in any measurements based on the single-beam propagation in DOFs.