Ultralow loss hollow-core conjoined-tube negative-curvature fiber

Hollow-core fiber (HCF) has found plenty of interdisciplinary applications in areas ranging from ultra-intense pulse delivery, single-cycle pulse generation, low latency optical communication, UV light sources, mid-IR gas lasers to biochemical sensing, quantum optics and mid-IR to Terahertz waveguides. These applications calls for better performance HCF, especially in loss, bandwidth and mode quality. Here we present a new hollow-core fiber with conjoined-tubes in the cladding and a negative-curvature core shape. It exhibits a minimum transmission loss of 2 dB/km at 1512 nm and a <16 dB/km bandwidth covering the O, E, S, C, L telecom bands. The debut of this conjoined-tube hollow-core fiber, with combined merits of ultralow loss, broad bandwidth, low bending loss, high mode quality and simple structure heralds a new opportunity to fully unleash the potential of hollow-core fiber in laser and telecommunication related applications.