The polarization direction-dependent SBS threshold was investigated, and the terminal polarization control technique was demonstrated to restore the linear polarization state. By increasing the relative angle of the injecting polarization direction from 0° to 90°, the measured SBS threshold increased until reaching a maximum value, beyond which it decreased in a nearly symmetrical trend. The highest SBS threshold was achieved with the relative polarization angle being 45°, delivering a 67% threshold enhancement compared with that at 0°. A quarter-wave-plate was used to restore the polarization state of the output laser manually from an elliptic to a linearly polarized state, and temperature-dependent polarization fluctuation was observed, which intensified as the laser power was scaled. By reducing the cooling temperature, a 1 kW laser with a linearly polarized state was demonstrated using a 45° polarization direction-injected monolithic PM amplifier.
