Divergence-degenerate spatial multiplexing towards future ultrahigh capacity, low error-rate optical communications

Area of Science:

• Optics and Photonics
• Optical Communications
• Information Theory

Background:

• Spatial mode (de)multiplexing using orbital angular momentum (OAM) beams is crucial for increasing bandwidth in optical communication.
• The divergence of OAM modes increases with mode order, limiting the number of addressable spatial channels.
• Existing methods face challenges in scaling capacity due to mode divergence and propagation inconsistencies.

Purpose of the Study:

• To introduce a novel set of multi-vortex geometric beams (MVGBs) as high-dimensional information carriers for free-space optical communication.
• To overcome the limitations of OAM mode divergence and enhance the capacity of optical communication systems.
• To demonstrate the feasibility of MVGBs for increasing the number of addressable spatial channels.

Main Methods:

• Developed a new modal basis set of multi-vortex geometric beams (MVGBs).
• Utilized three independent degrees of freedom (DoFs): central OAM, sub-beam OAM, and coherent-state phase.
• Experimentally realized tri-DoF MVGB mode (de)multiplexing and data transmission using conjugated modulation.

Main Results:

• MVGBs exhibit high divergence degeneracy and consistent propagation behaviors across all spatial modes.
• Predicted increase in addressable spatial channels by two orders of magnitude compared to OAM basis.
• Experimental demonstration showed lower error rates for MVGBs compared to OAM basis, especially concerning center offset and background noise.

Conclusions:

• MVGBs offer a promising solution for high-dimensional information carriers in free-space optical communication.
• The proposed modal basis significantly enhances the capacity and robustness of optical communication systems.
• This work lays the foundation for next-generation large-scale dense data communication.