LAUSR

We report a 7-tube single-ring hollow-core anti-resonant fiber (SR-ARF) with a record low transmission loss of 4.3 dB/km @1080 nm, which is almost half of the current lowest loss record of an SR-ARF (7.7 dB/km @750 nm). The 7-tube SR-ARF has a large core diameter of 43 µm and a wide low-loss transmission window exceeding 270 nm for the 3-dB bandwidth. Moreover, it exhibits an excellent beam quality with an M2 factor of 1.05 after 10-m-long transmission. The robust single-mode operation, ultralow loss, and wide bandwidth make the fiber an ideal candidate for short-distance Yb and Nd:YAG high-power laser delivery.