OAM mode multiplexing in weakly guiding ring-core fiber with simplified MIMO-DSP

Area of Science:

• Optical Communications
• Photonics
• Fiber Optics

Background:

• Orbital Angular Momentum (OAM) offers a new dimension for increasing fiber optic communication capacity.
• Current OAM fiber designs often suffer from high crosstalk and require complex digital signal processing (DSP).
• Mode Group Multiplexing (MGM) is a promising technique for enhancing spectral efficiency in optical networks.

Purpose of the Study:

• To present a novel low-loss weakly guiding ring-core fiber for OAM-MGM transmission.
• To demonstrate a fiber design that minimizes inter-modal crosstalk and simplifies signal processing requirements.
• To achieve high spectral efficiency with reduced complexity in optical communication systems.

Main Methods:

• Designed a ring-core fiber with a 0.7% relative refractive index difference supporting 50 radially fundamental modes.
• Achieved effective refractive index differences (Δneff) greater than 10⁻⁴ between most OAM mode groups.
• Investigated the fiber's dispersion and mode area characteristics across the C+L band.

Main Results:

• The fiber supports 50 modes divided into 13 OAM mode groups with low inter-group crosstalk.
• OAM mode groups can be used for MGM without complex multiple-input multiple-output digital signal processing (MIMO-DSP).
• The fiber exhibits low, flat dispersion (14.3–39.7 ps/nm/km) and a large mode area (787.9–841.2 µm²).

Conclusions:

• The proposed ring-core fiber enables efficient OAM-MGM transmission with significantly reduced MIMO-DSP complexity.
• Intra-group modes can carry different data using small-scale MIMO, while inter-group modes can be used without MIMO.
• This fiber design represents a significant advancement towards higher capacity and more manageable optical communication systems.