Self-protecting index-adapting cladding light stripper

Refractive index (RI) based cladding light strippers (CLS) are a quick to apply solution for on-site laboratory laser testing that can strip light with low numerical aperture (NA) due to fiber bending. However, particularly at the 2 µm wavelength range for Thulium lasers, most materials suffer from high absorption, limiting conventional high-RI CLS to a few W of input power. By using a material with a high negative thermo-optical coefficient (TOC), the input power handling capability can be increased significantly by spreading the heat load evenly along a long fiber length. The maximum stripped power of the self-index-adapting CLS is limited by its length and it transmits excess input power, protecting itself from overheating. Backed by a numerical model for straight CLS, 12.9 W of stripped power at 2039 nm with an efficiency of >40 dB is reached experimentally in a bent configuration on a 15 cm long heatsink.