Dynamic vortex mode-switchable erbium-doped Brillouin laser pumped by high-order mode.

We experimentally demonstrated that the transversal vortex modes of an all-fiber erbium-doped Brillouin laser can be dynamically switched by using the high-order mode (HOM) of Brillouin pump (BP), which is used to achieve the oscillation of HOM inside the ring cavity. Core-mode conversion in a few-mode fiber (FMF) between the fundamental mode and HOM is obtained by cascading an acoustically induced fiber grating (AIFG) and a mode selection coupler (MSC) operating at the same wavelength region. Through frequency shift keying (FSK) modulation of the AIFG signal, the output transversal modes can be switched dynamically between and vortex modes, and the measured purities of output HOM are more than 82%. Moreover, the output Brillouin wavelength can also be tuned via altering the input wavelength of BP and the resonant response of AIFG. We have achieved HOM Brillouin-shifted laser output within the wavelength band from 1545-1560 nm. The output linewidth of the proposed Brillouin laser is less than 4 kHz.