Bending loss characterization in nodeless hollow-core anti-resonant fiber.

We report high performance nodeless hollow-core anti-resonant fibers (HARFs) with broadband guidance from 850 nm to >1700 nm and transmission attenuation of ~100 dB/km. We systematically investigate their bending loss behaviors using both theoretical and experimental approaches. While a low bending loss value of 0.2 dB/m at 5 cm bending radius is attained in the long wavelength side (LWS) of the spectrum, in this paper, we pursue light guidance in the short wavelength side (SWS) under tight bending, which is yet to be explored. We analytically predict and experimentally verify a sub transmission band in the SWS with a broad bandwidth of 110 THz and an acceptable loss of 4.5 dB/m at 2 cm bending radius, indicating that light can be simultaneously guided in LWS and SWS even under tight bending condition. This provides an unprecedented degree of freedom to tailor the transmission spectrum under a tight bending state and opens new opportunities for HARFs to march into practical applications where broadband guidance under small bending radius is a prerequisite.