Ring-core fiber with negative curvature structure supporting orbital angular momentum modes

Area of Science:

• Photonics
• Optical Fiber Technology
• Materials Science

Background:

• Photonic crystal fibers typically use positive curvature structures for light confinement.
• Negative curvature structures offer superior light confinement compared to positive curvature.
• Shifting the confinement medium from cladding to a specialized structure is a novel approach.

Purpose of the Study:

• To investigate and fabricate a negative curvature ring-core fiber for enhanced light confinement and mode filtering.
• To explore the relationship between outer tube thickness and vector eigenmode confinement.
• To achieve low loss transmission of orbital angular momentum (OAM) modes.

Main Methods:

• Theoretical analysis of vector eigenmodes and threshold values for outer tube thickness.
• Simulation-guided design and fabrication of the negative curvature ring-core fiber.
• Vacuum drawing techniques for central cane and fiber preform fabrication.
• Experimental testing of donut facula formation and loss measurements for OAM modes.

Main Results:

• Demonstrated that outer tube thickness can be used to confine target modes and filter unwanted ones.
• Successfully fabricated the negative curvature ring-core fiber using vacuumization methods.
• Determined that a fiber length of 15-20 m is required to form a donut facula.
• Achieved low propagation losses for OAM modes: 0.30 dB/m for OAM+1,1, 0.36 dB/m for OAM+2,1, 0.37 dB/m for OAM+3,1, and 0.42 dB/m for OAM+4,1.

Conclusions:

• Negative curvature ring-core fiber provides an effective platform for achieving strong light confinement.
• The outer tube thickness is a critical parameter for selective mode filtering in this fiber design.
• The fabricated fiber exhibits low loss for high-order orbital angular momentum modes, suitable for advanced optical applications.