Abstract

The development of thulium-doped fibre lasers (TDFL) is motivated by numerous potential applications in spectroscopy, remote sensing, medicine, material processing, and telecommunications. The all-fibre core-pumped ring cavity TDFLs exploiting fiberized grating-based filter [1] or Fabry-Pérot etalon [2] as a wavelength selective element were reported. An optical isolator should be inserted into the fibre ring cavity to ensure unidirectional lasing. Isolator-free unidirectional ring fibre cavity (sometimes referred to “theta” [3] or “yin-yang” [4] resonators) represents an attractive and cost-effective alternative solution. In theta cavities, nonreciprocal losses are introduced by providing an S-shape feedback within the main ring. An erbium doped fibre laser (EDFL) with theta cavity, providing close to 20 dB extinction ratio (ER) between output signals, propagating in favoured and suppressed directions, was demonstrated [5]. We report for the first time the demonstration of a unidirectional 2 μm TDFL, exploiting properties of the theta cavity.

© 2015 IEEE