Technique for continuous tuning of optical fiber lasers

For the first time to the authors' knowledge, we have demonstrated how thermally controlled overcoupled fused fiber couplers and fiber loop mirrors based on these couplers can be used as broadband tuning elements in a fiber laser cavity. No bulk optical elements play any role in this technique. Temperature tuning the coupler results in a shift in the coupling ratio or in the effective output coupler transmission. For a fixed pump source, and for a given laser cavity, this shift causes the lasing wavelength to shift. We have continuously tuned an Er silica fiber laser in this manner over the range of 1527-1570 nm in a ring configuration, and, using a fiber loop mirror with these couplers in a linear Tm silica fiber laser cavity, we have achieved more than 50-nm broadband tuning over the range of 1850-1910 nm. The tuning range and the sensitivity to temperature depend on the degree of overcoupling of the loop mirror coupler.