Ultra-Broadband Mode Conversion With Acousto-Optic Coupling in Hole-Assisted Fiber

This paper describes the acousto-optic properties of hole-assisted fibers (HAFs) numerically and experimentally. We show that the HAF beat length between the guided and first higher-order modes has small wavelength dependence compared with that of the single mode fiber and so we can achieve broadband acousto-optic coupling. Ultra-broadband acousto-optic coupling is realized by using a HAF with flattened beat length characteristics. The coupling bandwidth reaches 120 nm, and can be controlled by designing the air hole structure.