Fig. 1. Backscattered optical power as a function of fiber length for the MMF-RFG, located about 1.88 m from the connector of the OBR (a) and reflected power as a function of the wavelength for the MMF-RFG reflector (b).

Fig. 2. Schematic diagram of the experimental L-band linear-cavity fiber laser setup; (a) pump laser; (b) wavelength-division multiplexer; (c) erbium-doped fiber; (d) fiber optic circulator; (e) optical coupler; (f) optical spectrum analyzer; (g) high-precision rotation mount where the MMF-RFG was rotated; (h) photograph of the inscribed MMF-RFG located into a syringe.

Fig. 3. Relationship between the output-power levels versus 976-nm pump power when (a) single-wavelength operation centered at 1574.75 nm (blue line) or at 1575.75 nm (red line) and (b) dual-wavelength operation were obtained.

Fig. 4. Output spectra of the linear-cavity fiber laser with a MMF-RFG reflector pumped by a 976-nm laser, when (a) a single wavelength lasing centered at 1574.75 nm, (b) a dual wavelength lasing centered at 1574.75 nm and 1575.75 nm, and (c) a single wavelength lasing centered at 1575.5 nm are obtained. (d) Electric beat with a tunable laser source (TLS) of the single-wavelength lasing emission when pumped at 300 mW.