“…Particularly, due to their prominent spectral re-configurability by respectively controlling the amplitude and frequency of the applied radiation frequency (RF) signal for acoustic wave generation, all-fiber acousto-optic tunable filters (AOTFs) based on acoustically induced LPGs have attracted considerable research interest in such dynamically evergrowing fields as optical communications [4,5], optical fiber sensing applications [6,7], optical fiber lasers [8], and even slow and fast light control implementations [9]. Factually, besides the acoustically induced long-period fiber gratings, the interaction between light and sound in bulk media has also been extensively investigated and many related AOTFs have been developed in the past few years [10][11][12]. And owing to their distinguished properties such as compact size, ease of fabrication and flexibility of acoustically controlled optical processes, besides the applications as single optical elements, fiber-based AOTFs have also been applied in mode coupling process control in various fiber-optic components, such as LPGs [13], fiber Bragg gratings (FBGs) [14], tilted fiber Bragg gratings (TFBGs) [15], tapered fiber structures [16], etc.…”