Single-End-Pumped Tm3+:Ho3+-Codoped all-Fiber Laser at 2120 nm

Efficient high-power lasers emitting at a wavelength of around 2.12
$\upmu \mathrm{m}$
are of increasing interest for applications taking advantage of a broad atmospheric transmission window. Typically, Ho
³⁺
-doped fiber lasers (HDFL) are used to address this wavelength region due to much higher emission cross sections compared to their 2
$\upmu \mathrm{m}$
equivalent Thulium lasers [1], [2]. Recently, Tm
³⁺
:Ho
³⁺
-codoped fiber lasers were demonstrated with a slope efficiency as high as 56 % [3] and output powers up to 260 W [4], thus making them a sound substitute to HDFLs for operation above 2.1
$\upmu \mathrm{m}$
. The free-space setup shown in [4] is now transferred to a more integrated and rugged all- fiber version. To the best of our knowledge, we show the first realization of a Tm
³⁺
:Ho
³⁺
-codoped all-fiber laser emitting at 2120 nm with a slope efficiency close to 50 %.