Digital Frequency-Domain MIMO Equalizer Enabling Six-LP-Mode Strong-Coupling IM/DD MDM Optical Transmission System.

Area of Science:

• Optical communications engineering
• Signal processing for optical networks

Background:

• Mode division multiplexing (MDM) enhances capacity in short-reach optical systems like data centers.
• Mode coupling in MDM systems degrades signal quality, necessitating solutions like weakly coupled components or optical MIMO equalizers.

Purpose of the Study:

• To explore pure digital signal processing (DSP) for mode decoupling in intensity modulation/direct detection (IM/DD) MDM systems with strong mode coupling.
• To propose and verify a frequency-domain multiple-input-multiple-output (MIMO) equalizer for compensating modal interference.

Main Methods:

• Numerical simulations to verify the signal recovery capability of the frequency-domain MIMO equalizer.
• Experimental demonstration of a six-linear-polarized (LP) mode strong-coupling IM/DD MDM system over 10 km of few-mode fiber.
• Utilizing a pair of strong-coupling mode multiplexers/demultiplexers.

Main Results:

• Successful transmission of on-off-key (OOK) signals in a challenging six-LP-mode strong-coupling MDM IM/DD system.
• All modes' OOK signals were recovered with a hard-decision forward error correction threshold of 8.3 × 10-3.
• Demonstrated the effectiveness of the frequency-domain MIMO equalizer in mitigating modal interference.

Conclusions:

• The proposed frequency-domain MIMO equalizer, implemented via DSP, effectively compensates for modal interference in strong-coupling MDM IM/DD systems.
• This DSP-based approach offers a flexible and practical alternative for enhancing short-reach communication systems.
• The method holds potential for advancing the practical application of MDM techniques in future optical networks.