All-fiber stable orbital angular momentum beam generation and propagation

Area of Science:

• Optical communications
• Photonics
• Fiber optics

Background:

• Orbital angular momentum (OAM) multiplexing offers increased data capacity.
• Generating and maintaining OAM beams in fiber systems remains challenging.
• Existing methods often lack stability or require complex setups.

Purpose of the Study:

• To propose and demonstrate a stable all-fiber scheme for generating and propagating orbital angular momentum (OAM) beams.
• To develop a system compatible with mode division multiplexing (MDM) applications.
• To achieve high-purity OAM beam propagation over a wide bandwidth.

Main Methods:

• Utilized a self-designed graded-index few-mode fiber (GI-FMF).
• Employed a mode selection coupler (MSC) for efficient fundamental-to-OAM mode conversion.
• Leveraged phase matching conditions for selective mode excitation.
• Designed GI-FMF to break mode degeneracy for stable propagation.

Main Results:

• Successfully implemented an all-fiber device for stable OAM (|l|=1) generation and propagation.
• Achieved OAM beam propagation with approximately 95% mode purity.
• Demonstrated a wide operational bandwidth of 100 nm.
• Confirmed stable propagation of selectively excited OAM modes.

Conclusions:

• The proposed all-fiber scheme enables stable generation and propagation of OAM beams.
• The developed GI-FMF and MSC provide high mode purity and a broad bandwidth.
• This technology is promising for advancing wide-bandwidth OAM mode division multiplexed applications.