High-order optical vortex generation in a few-mode fiber via cascaded acoustically driven vector mode conversion

Area of Science:

• Optics and Photonics
• Fiber Optics
• Acousto-Optics

Background:

• Optical vortices, characterized by helical phase fronts, have applications in optical manipulation, communication, and microscopy.
• Generating high-order optical vortices efficiently and controllably in optical fibers remains a challenge.

Purpose of the Study:

• To propose and experimentally demonstrate a method for generating high-order optical vortices in few-mode fibers.
• To utilize cascaded acoustically driven vector mode conversion for precise vortex generation.

Main Methods:

• Theoretical analysis of vector mode conversion between HE modes using acoustically induced fiber gratings (AIFGs).
• Experimental implementation using two simultaneously induced AIFGs in a few-mode fiber at 532 nm.
• Cascaded conversion of fundamental circular polarization modes to ±1-order and subsequently to ±2-order vortex modes.

Main Results:

• Demonstrated efficient conversion of fundamental modes to ±1-order vortex modes using the first AIFG.
• Achieved further conversion to ±2-order vortex modes using the second cascaded AIFG.
• Verified the topological charges of generated vortex modes using coaxial and off-axial interference, observing characteristic spiral and forklike fringe patterns.

Conclusions:

• The proposed method effectively generates high-order optical vortices in few-mode fibers.
• Cascaded AIFGs offer a precise and controllable approach for optical vortex generation.
• The experimental verification confirms the theoretical predictions and the capability of the technique.