Abstract
Abstract The burgeoning advances of spatial mode conversion in few-mode fibers emerge as the investigative hotspot in novel structured light manipulation, in that, high-order modes possess a novel fundamental signature of various intensity profiles and unique polarization distributions, especially orbital angular momentum modes carrying with phase singularity and spiral wave front. Thus, control of spatial mode generation becomes a crucial technique especially in fiber optics, which has been exploited to high capacity space division multiplexing. The acousto-optic interactions in few-mode fibers provide a potential solution to tackle the bottleneck of traditional spatial mode conversion devices. Acousto-optic mode conversion controlled by microwave signals brings tremendous new opportunities in spatial mode generation with fast mode tuning and dynamic switching capabilities. Besides, dynamic mode switching induced by acousto-optic effects contributes an energy modulation inside a laser cavity through nonlinear effects of multi-mode interaction, competition, which endows the fiber laser with new functions and leads to the exploration of new physical mechanism. In this review, we present the recent advances of controlling mode switch and generation employing acousto-optic interactions in few-mode fibers, which includes acousto-optic mechanisms, optical field manipulating devices and novel applications of spatial mode control especially in high-order mode fiber lasers.
Highlights
Spatial modes composed by cylindrical vector modes (CVMs), linear polarization (LP) modes and optical vortex modes exhibit special distributions of electrical fields existing stably in optical fibers [1,2,3]
We present the recent advances of controlling mode switch and generation employing acousto-optic interactions in few-mode fibers, which includes acousto-optic mechanisms, optical field manipulating devices and novel applications of spatial mode control especially in high-order mode fiber lasers
We summarize the new mechanisms of dynamic mode switching based on Acousto-optic mode converters (AOMCs) and the applications incorporated with high-order modes (HOMs) fiber lasers
Summary
Spatial modes composed by cylindrical vector modes (CVMs), linear polarization (LP) modes and optical vortex modes exhibit special distributions of electrical fields existing stably in optical fibers [1,2,3]. Periodic refractive index change is applied in fibers to realize mode conversion from forward propagating fundamental mode to forward propagating HOMs in LPGs [35] or backward propagating HOMs in FBGs [39] These methods can demonstrate high efficiency of mode conversion, but their limited versatility of static generation of spatial modes greatly constrains the application domain of HOM light sources. The pioneered discovery in 1986 that Kim et al firstly proposed and demonstrated the mode conversion with a frequency shift by a two-mode fiber-based AOMC [43], which has opened a door to novel researches on acousto-optic interactions (AOI) in fibers and various derived components. We summarize the new mechanisms of dynamic mode switching based on AOMCs and the applications incorporated with HOM fiber lasers.
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