Fig. 1: Research progress of all-fiber single-frequency lasers.

(D-shaped fiber (DF), Chirally-Coupled-Core air-clad fiber (CCCA), photonic crystal fiber (PCF) and all-solid photonic bandgap fiber (APBF), step-index fiber (SIF), Chirally-Coupled-Core fiber (CCC), confined-doped fiber (CDF), tapered active fiber (T-F), cascade active fibers (C-F))