Fiber coupler for generating orbital angular momentum modes.

Area of Science:

• Optics and Photonics
• Optical Communications
• Waveguide Technology

Background:

• Orbital angular momentum (OAM) modes offer potential for increased data capacity in optical communications.
• Efficient generation and manipulation of multiple OAM modes in fiber are crucial for practical applications.

Purpose of the Study:

• To propose and demonstrate a novel fiber coupler for generating multiple OAM modes.
• To achieve high-purity OAM mode generation in a compact fiber-based device.
• To explore the potential for all-fiber spatial-mode (de)multiplexing.

Main Methods:

• A fiber coupler design featuring a central ring and four external cores was proposed.
• Coherent input lights were launched into external cores and coupled into the central ring.
• The size of external cores was adjusted to selectively excite high-order OAM modes.
• Polarization state and phase of input lights were optimized to enhance OAM mode quality.

Main Results:

• Generation of 10 OAM modes with odd charge numbers from -9 to +9 was demonstrated.
• Mode purity exceeding 99% was achieved.
• The fiber coupler length was less than 2 mm.
• Selective excitation of high-order OAM modes was confirmed by adjusting external core size.

Conclusions:

• The proposed fiber coupler enables efficient generation of multiple high-purity OAM modes.
• The design is scalable and can be extended for all-fiber spatial-mode (de)multiplexing.
• This technology holds promise for advancing optical communication capacity and functionality.