Fig. 1. Typical sketch of a tapered fiber, where w and D are diameters of the waist and conventional SMF, respectively; the repetition length Ltaper is the distance between two adjacent tapers; lwaist, ltrans, and ltaper are the lengths of the waist region, transition region, and tapered region.

Fig. 2. Simulation results: (a) Aeff and BFS versus core radius: (b) BGS versus waist, (c) total generated Stokes power versus waist, (d) BGS versus rtaper, and (e) total generated stokes power versus rtaper.

Fig. 3. Experimental results of SBS suppression method: (a) experimental setup; (b)–(e) theoretical/experimental power ratio between the SBS and Rayleigh scattering peaks versus rtaper when the waist is 105, 90, 75, and 60 μm, respectively; (f) optical power spectra of backward-scattered light in conventional SMF and tapered fibers (rtaper=0.02 and w=75  μm) with the same pump power.

Fig. 4. Variation tendency of the scattered optical power when the optical power of incident light changes.

Fig. 5. Schematic diagram of the tunable STRS-based SLM laser with ultranarrow linewidth.

Fig. 6. Spectra detected by delayed self-heterodyne method: (a) without secondary cavities, (b) with secondary cavities, (c) without linewidth compression device, and (d) with linewidth compression device.