Large-mode-area multi-resonant all-solid photonic bandgap fiber with low bending loss and robust single-mode operation

In this paper, we have experimentally demonstrated a novel large-mode-area multi-resonant all-solid photonic bandgap fiber (AS-PBGF) which is specifically optimized for conventional applications of fiber lasers around 1 mu m, with a hexagon core that is measured to be 46 mu m in the corner-to-corner direction and a broad bandwidth from 970 nm to 1180 nm in the 3rd photonic bandgap (PBG). Bending loss lower than 0.1 dB/m of a 5-m-length fiber is obtained in the case of bending radius R greater than 25 cm. Robust single-mode (SM) operation of the fiber is verified within the whole PBG. In addition, we also report a phenomenon about the abnormal variation of M-2 within the low loss region of the 3(rd) PBG. The evolution of beam quality within the 3(rd) PBG appears as a U-shaped curve rather than a constant. Finally, a preliminary conclusion about the relationship between the beam quality and SM characteristics in AS-PBGF which is quite different from that in conventional SIFs is verified.