All-Solid Photonic Bandgap Fiber for Efficient Suppression of Stimulated Brillouin Scattering

Stimulated Brillouin scattering (SBS) has become a major bottleneck restricting the agile delivering of high-power narrow-linewidth lasers in practical applications. We demonstrate an all-solid photonic bandgap fiber (AS-PBGF) with core diameter of 20 μm to suppress the SBS effect. The designed structure comprises a five-layer hexagonal array of high-index Ge-doped rods embedded within a silica matrix, and it operates in the 3rd photonic bandgap for the 1 μm spectral band. Through carry out comparative experiment, the AS-PBGF demonstrates a ∼30% higher SBS threshold than commercial step-index large-mode-area fiber (LMAF) of the same core diameter at a length of 75 m. Using the finite element method, the AS-PBGF is theoretically calculated to have smaller acousto-optic overlap factor and Brillouin gain coefficient than those of the LMAF, which further verifies the SBS suppression capability of the AS-PBGF. Moreover, the output of the AS-PBGF is experimentally confirmed to maintain near-diffraction-limited beam quality even at high-power operation beyond the SBS threshold. To the best of our knowledge, this is the first experimental report on SBS suppression in passive silica-based AS-PBGFs, demonstrating their potential for high-power narrow-linewidth laser delivery.