Fig. 1. The schematic of the RFL. FBG, fiber Bragg grating; reflector, high reflectivity fiber coated reflector at 1.4 µm; WDM, 1238.90/1350 nm wavelength division multiplexer; Bi-doped fiber, bismuth-doped fiber; tunable filter, tunable filter (JDSU mTBF-A1) with 1420–1620 nm; ISO, optical isolator; FC-APC, fiber end facets with 8°; PDF, phosphorus-doped fiber; YDF, ytterbium-doped fiber; OC, optical coupler; combiner, double-cladding pump combiner.

Fig. 2. (a) Emission spectrum of Bi-doped fiber; (b) spectrum of 1238.90 nm Raman fiber laser.

Fig. 3. (a) Optical spectrum of Bi-doped RFL; (b) Bi-doped RFL output power versus pump power at 1352.03 nm; (c) long-time output power stability of the RFL for 1 h; (d) RF spectrum of the RFL state; inset, the RF spectrum of convention cavity.

Fig. 4. (a) Speckle pattern of Bi-doped RFL; (b) speckle pattern of Bi-doped conventional fiber laser; (c) wavelength-tuning optical spectrum from 1352.03 to 1356.03 nm; (d) wavelength-tuning optical spectrum from 1419.20 to 1467.19 nm.

Fig. 5. (a) Bi-doped RFL output power versus pump power at 1455.82 nm; (b) multiwavelength of the Bi-doped RFL.