Precompensation of the thermal-induced refractive index changes into a fully aperiodic LPF for heat load resilience.

In this paper, a strategy consisting of precompensating the thermal-induced transverse refractive index changes is undertaken to push further the appearance threshold of a multimode regime. First, a standard air-silica large pitch fiber (LPF) and a fully aperiodic large pitch fiber are confronted in regard to their heat load resilience and capabilities for single-mode emission. Thereafter, slight refractive index depressions are judiciously introduced into the active core area. This approach enhances the delocalization of the high-order modes even under severe heat load levels. This combination of aperiodic cladding microstructuration and index-precompensation theoretically increases the multimode regime threshold while preserving large mode field areas. This investigation is performed at 1.03 and 2 µm operating wavelengths.