Highly efficient, depressed-cladding thulium-doped fiber laser at 1762 nm

A continuous-wave (CW) multi-watt-level 1.76-μm all-fiber Tm-doped laser resonantly pumped at 1.56 μm is presented. To mitigate long-wavelength amplified spontaneous emission (ASE), an in-house-drawn depressed-cladding Tm-doped fiber (dc-TDF) was used as an active medium. In a linear cavity, an output power of 2.47 W, with an optical signal-to-noise ratio (SNR) exceeding 65 dB and a high slope efficiency of 75.8% relative to the launched power, was demonstrated. Furthermore, bidirectional pumping enabled output power scaling over 4 W with a slope efficiency of 66%. To our knowledge, this is the first demonstration of 1.7-μm laser operation using dc-TDFs.