Fig. 1. (a) Alignment of FBG principal axes, forming dual-polarization resonators. (b) Orthogonal splicing of FBGs to enable single-polarization oscillation by suppressing the orthogonal mode.

Fig. 2. Schematic diagram of the PM Tm-doped all-fiber laser architecture, comprising an oscillator with 10/130 µm fiber and a power amplifier with 15/250 µm fiber, operating in single-mode at 1908 nm.

Fig. 3. (a) Output power and backward power versus launched pump power. (b) Laser spectra at oscillator PERs of 18.8 dB (solid line) and 1.8 dB (dashed line).

Fig. 4. Polarization of the oscillator measured under varying HR-FBG and LR-FBG temperature settings. The temperature range for both HR-FBG and LR-FBG spans 15°C–35°C, controlled using TECs.

Fig. 5. Average slope efficiency as a function of active fiber length in the MOPA configuration, along with maximum output power levels at which fiber fuse initiated.

Fig. 6. Optical spectra of the amplifier measured at 81 W for a 3.4 m fiber, 147 W for a 3.1 m fiber, and 205 W for a 2.7 m fiber.

Fig. 7. MOPA output power as a function of launched and absorbed pump powers, with corresponding slopes and optical efficiencies shown for both cases.

Fig. 8. M² values and beam profiles (insets) at output powers of 50, 150, and ∼200 W.

Fig. 9. Long-term power stability and PER measurements. The inset shows the histogram of the power data.