Numerical Investigation of the Interaction of Tubular Hollow-Core Fibers and Flexural Acoustic Waves

The modulation efficiency of a tubular-lattice hollowcore fiber (HCF) employing flexural acoustic waves is investigated in detail for the first time. The main acousto-optic properties of the HCF are evaluated, using 2D and 3D models based on the finite element method. The induced coupling of the fundamental and first higher-order modes is simulated from 743 to 1355 nm. The most relevant acoustic (amplitude, period, strain, energy) and optical (effective index, beat length, birefringence, coupling coefficient) parameters are analyzed. The simulations are compared to experimental results and indicate higher modulation performance in HCFs compared to standard optical fibers. In addition, useful insights into the design and fabrication of all-fiber acousto-optic devices based on HCFs are provided, enabling potential application in tunable spectral filters and mode-locked fiber lasers.