Thermo-Optical Effects in Tm-Doped Large mode Area Photonic Crystal Fibers

Designs of Tm-doped photonic crystal fibers for laser operation must take in account the strong thermo-optical effects due to the Tm quantum defect and the consequent corruption of the single mode guiding properties. A new fiber design with a similar to 80 mu m core diameter, based on the cladding mirror symmetry reduction is proposed and analyzed using a full-vector FEM-based modal solver. The thermal effects are investigated using a computationally efficient model. A large pitch fiber with similar core diameter, which represents the actual state-of-art of Tm-doped laser technology, has been investigated in order to have a basis of comparison. Optimizing some key parameters of the new symmetry free fiber, the possibility to achieve a wide band single mode operation under an heavy heat load of over 300 W/m is demonstrated. In particular a very high modal discrimination value larger than 0.5 is obtained.