Third- and fourth-order orbital angular momentum multiplexed amplification with ultra-low differential mode gain

Area of Science:

• Optical Fiber Communications
• Photonics
• Waveguide Engineering

Background:

• Orbital Angular Momentum (OAM) multiplexing offers increased spectral efficiency in optical communications.
• Erbium-doped fibers (EDFs) are crucial for signal amplification in the C-band.
• Achieving low differential mode gain (DMG) is essential for practical OAM mode multiplexing.

Purpose of the Study:

• To design and fabricate a novel ring-core erbium-doped fiber (RC-EDF) capable of supporting and amplifying high-order OAM modes.
• To demonstrate efficient OAM mode multiplexed amplification with ultra-low DMG.
• To investigate the amplification characteristics of conjugate OAM modes.

Main Methods:

• Design and fabrication of a two-layer RC-EDF supporting up to the fourth-order OAM mode.
• Characterization of modal intensity and phase distribution.
• Measurement of modal gain under fundamental mode core pumping.
• Analysis of amplification performance for OAM_±3,1 and OAM_±4,1 modes.

Main Results:

• Demonstrated amplification of third- and fourth-order OAM modes with ultra-low DMG (<1 dB).
• Achieved an average gain of >19 dB for multiplexed OAM modes across the C-band.
• Observed consistent gains for conjugate OAM modes irrespective of simultaneous or separate amplification and pump power.

Conclusions:

• The developed RC-EDF is effective for OAM mode multiplexed amplification.
• Ultra-low DMG is achievable for high-order OAM modes using the proposed fiber structure.
• The findings support the advancement of high-capacity optical communication systems using OAM multiplexing.