Differential mode-gain equalization for FM-EDFA with real-time on-demand mode pumping via spatial light modulator

Area of Science:

• Optical Communications
• Fiber Optics
• Photonics

Background:

• Mode division multiplexing (MDM) is crucial for increasing fiber optic communication capacity.
• Few-mode fiber amplifiers (FM-EDFAs) are essential components for MDM systems.
• Controlling differential modal gain (DMG) is a key challenge in FM-EDFA development.

Purpose of the Study:

• To demonstrate a real-time, on-demand mode-pumped FM-EDFA.
• To achieve reconfigurable differential mode gain control.
• To analyze the impact of different pump modes on gain characteristics.

Main Methods:

• Development of a 980 nm high-order mode excitation platform using a spatial light modulator (SLM).
• Online conversion of single-mode pump laser output into various higher-order modes (LP11a, LP11b, LP21a, LP21b, LP02).
• Analysis of gain characteristics under individual and mode-multiplexed amplification with different pump modes.

Main Results:

• Achieved an average gain of 21.21 dB with a low DMG of 0.335 dB at 1550 nm using LP02 pump mode.
• Maintained DMG below 0.77 dB for signal input variations from -20 to -10 dBm.
• Obtained an average gain of 20.86 dB with DMG < 2.47 dB over the C-band for 8 amplified wavelength channels.
• Observed significant DMG differences when using azimuthal-dependent pumps.

Conclusions:

• The developed FM-EDFA with reconfigurable mode control enables effective DMG equalization.
• This technology supports the expansion of MDM transmission to more channels and longer distances.
• The findings provide valuable guidance for future MDM system development.