Tunable Tm/Ho-codoped fiber lasers based on an extensible liquid core between a pair of fused multimode-single-mode fibers.

We present mechanically tunable Tm/Ho-codoped fiber lasers based on multimode interference in single mode-multimode-single-mode structures. The intermediate multimode fiber (MMF) is separated into two segments with a liquid core in between. The mode field diameter of the single-mode fiber is designed to 13 µm for the MMF having a core diameter of 105 µm. The tunable range is attained to 64 nm by extending the effective length of the MMF. The laser wavelength is tuned over the ranges of 1809-1866 nm and 1866-1930 nm for the initial MMF lengths of 35.3 and 34.5 mm, respectively.