Specifics of spectral loss measurement in infrared fibers

Main error sources and their contribution to the total error of measuring the optical loss spectrum by the cut-back method are analyzed in the mid-IR range (2-20 μm) for multimode optical fibers made from materials with high (2-4) refractive index values. It is shown that in case of insufficient fiber length, neglecting the refractive index value leads to a systematic overestimation of the measured optical losses: the higher the refractive index of a fiber core material, the greater an overestimation. The main errors are typically introduced by a bad repeatability of preparation quality of fiber ends and a lower signal-to-noise ratio of mid-IR range experimental setups in comparison with the near-IR range.