Chalcogenide Fabry–Perot Fiber Tunable Filter

We demonstrate the first mid-infrared compatible all-fiber Fabry–Perot filter. It consists of chalcogenide fibers terminated with high-reflective coatings made of germanium and calcium fluoride. In addition to the transmission compatibility with mid-infrared wavelength, the filter has both tunability and free spectral range >350 nm as well as a finesse of 27. To demonstrate the application of the filter, a thulium-doped fiber laser is built and shows continuous tunability from 1.835 to 1.920
$\mu \text{m}$
.