Focused vortex beam generator suitable for optical fiber spanners in a complex liquid environment

Area of Science:

• Photonics and Optics
• Fiber Optics
• Nanofabrication

Background:

• Focused vortex beams (FVBs) offer unique properties for optical manipulation and information transfer.
• Generating FVBs directly within optical fibers presents challenges in miniaturization and environmental robustness.

Purpose of the Study:

• To experimentally demonstrate an all-fiber focused vortex beam (FVB) generator.
• To achieve efficient generation of high-order orbital angular momentum (OAM) modes.
• To assess the performance of the FVB generator in complex liquid environments.

Main Methods:

• Fabrication of a spiral zone plate (SZP) on the end face of a hybrid fiber using focused ion beam (FIB) milling.
• Utilizing a gold (Au)-coated end face for enhanced processing efficiency.
• Theoretical design and experimental verification of focus length and topological charge.

Main Results:

• Successful generation of FVBs with designed topological charges (0, 1, and 2).
• Measured focal spot diameters of 2.2 µm, 4.4 µm, and 5.2 µm for topological charges 0, 1, and 2, respectively.
• Simulated results indicate stable focusing characteristics in various liquids.
• Achieved nearly ten times higher processing efficiency compared to previous methods due to the Au-coated film.

Conclusions:

• The developed all-fiber FVB generator effectively produces beams with desired characteristics.
• The generator shows promise for applications requiring optical fiber spanners in complex liquid environments.
• The FIB milling technique combined with an Au-coated film significantly enhances fabrication efficiency.