Cascaded Brillouin, Raman, and Four-Wave-Mixing Generation in a 1.06-μm Microsphere-Feedback Yb-Fiber Laser

We propose and experimentally demonstrate a compact microresonator-feedback single-frequency fiber laser at 1.06 μm, and further initiating different-type nonlinear lasing based on stimulated Brilliouin scattering, stimulated Raman scattering, and four-wave mixing (FWM). A silica microsphere with an ultrahigh Q-factor is employed in our experiment as a narrow bandwidth cavity mirror around 1.06 μm, and a generator of nonlinear optical effects subsequently. With the help of mode selection both from the silica microsphere and a fiber Bragg grating, single-frequency lasing with a linewidth as narrow as 281 kHz is obtained at 1.06 μm by employing 974-nm laser diode pumped Ytterbium-doped fiber as a gain medium. By optimizing the polarization states, controlling the coupling position between the fiber taper and microsphere as well as the pump power, three-order cascaded Brilliouin Stokes lasings at 1.06 μm, and cascaded Raman lasing at 1.12, 1.18 and 1.23 μm are realized, respectively. An FWM-based optical frequency comb (OFC) with a bandwidth ~31 nm is further realized with center wavelength of ~1.06 μm. Interestingly, a 1.18-μm-centered OFC with ~37-nm bandwidth is also generated assisted by the second-order Raman-gain.