Ytterbium-doped fibre lasers with tailored all-solid microstructured cladding

Although singlemode fiber lasers become a mature technology, enhancements, in terms of output power, spatial beam quality, bend insensitivity are still required. A major trend is to increase the active core area to increase the thresholds of nonlinear effects while ensuring a transverse singlemode behavior. Actually, increasing the active ions' concentration is also demanded since it allows a drastic reduction of the fiber length, everything being equal. Two non-exclusive strategies are laid out to overcome fiber laser limitations. On the one hand, it is demonstrated that surrounding a highly multimode active core by a properly designed microstructured cladding, exhibiting specific resonant features, allows the fiber laser to be operated in the singlemode regime. On the other hand, a large mode area photonic bandgap fibre is shown to lead to a transverse singlemode fiber laser with very good lasing efficiency.