Matched Filtering for MIMO Coherent Optical Communications with Mode-Dependent Loss Channels

Area of Science:

• Optical Communications
• Signal Processing
• Digital Communications

Background:

• Digital signal processors (DSP) are widely used for equalizing coherent optical communication systems employing spatial division multiplexing (SDM).
• Existing DSP approaches often neglect the impact of mode-dependent loss (MDL), a critical factor in SDM systems.
• Linear multiple-input multiple-output (MIMO) receivers are essential for advanced optical communication architectures.

Purpose of the Study:

• To develop and analyze a linear MIMO receiver for coherent SDM optical systems that optimizes minimum mean square error (MMSE).
• To investigate the system performance without prior assumptions on receiver oversampling or analog front-end limitations.
• To evaluate the influence of the transmitter's roll-off factor on system performance.

Main Methods:

• Design of a linear MIMO receiver focused on MMSE optimization for coherent SDM systems.
• Analysis of a simple match filter (MF) based MIMO receiver's capability to eliminate inter-symbol interference (ISI) and crosstalk.
• Numerical simulations evaluating a fractionally-spaced equalizer (FSE) MIMO receiver in MDL-impaired channels using novel signal-to-noise and distortion ratio (SNDR) loss metrics.

Main Results:

• Demonstrated that a MF-based MIMO receiver can completely eliminate ISI and crosstalk in SDM systems when MDL is negligible.
• Quantified the performance degradation in MDL-impaired channels using SNDR loss.
• Showcased performance improvements achievable by increasing the transmitter roll-off factor.

Conclusions:

• The proposed linear MIMO receiver framework effectively addresses equalization challenges in coherent SDM optical systems, even with non-negligible MDL.
• The study highlights the trade-offs between system parameters like the roll-off factor and performance metrics.
• This research provides valuable insights for designing robust optical receivers in advanced SDM communication networks.