All-fiber, narrow linewidth and linearly polarized fiber laser in a single-mode-multimode-single-mode cavity.

We report the design of an all-fiber, linearly polarized Yb-doped fiber laser at 1064 nm with a narrow linewidth and high output power required by the master oscillator of the amplifier for high-power spectral beam combining. The laser has achieved linearly polarized output with a polarization extinction ratio of 23 dB, a narrow linewidth of ≤52  pm, and an output power of 32.7 W. Such performance was obtained by the cavity design that incorporated a wavelength-shifted PM fiber Bragg grating pair and single-mode-multimode-single-mode structure.