  We demonstrate a broadband acousto-optic notch filter based on a
tubular-lattice hollow-core fiber for the first time. The guided optical modes
are modulated by acoustically induced dynamic long-period gratings along the
fiber. The device is fabricated employing a short interaction length (7.7 cm)
and low drive voltages (10 V). Modulated spectral bands with 20 nm half-width
and maximum depths greater than 60 % are achieved. The resonant notch
wavelength is tuned from 743 to 1355 nm (612 nm span) by changing the frequency
of the electrical signal. The results indicate a broader tuning range compared
to previous studies using standard and hollow-core fibers. It further reveals
unique properties for reconfigurable spectral filters and fiber lasers,
pointing to the fast switching and highly efficient modulation of all-fiber
photonic devices.
