MATCH

Multicore fibers are a promising route to scale optical capacity beyond the limits of single-mode fibers. However, conventional weakly coupled MCFs require high-dimensional MIMO equalization, which increases DSP complexity, power consumption, and latency.

Randomly-Coupled MCFs (RC-MCFs) behave differently:

• Optical power couples rapidly and randomly among cores
• This random coupling averages out differential delays
• The channel becomes effectively memoryless over long distances
• As a result, the required MIMO equalization collapses to a much smaller dimension, reducing DSP load dramatically

This makes RC-MCFs attractive for energy-efficient, scalable SDM systems, and also opens new possibilities for joint communication and sensing, since all cores experience similar perturbations.

Our work at INT investigates these properties experimentally and develops DSP methods tailored to strongly coupled fiber systems.

Our Role in MATCH

We study the performance of RC-MCFs under realistic conditions by building a full coherent transmission chain. This includes:

• Generation of high-baud-rate QPSK/16QAM waveforms using an AWG
• IQ modulation and optical upconversion
• Transmission over standard SMF (baseline) and later over RC-MCF samples
• Coherent detection using a high-speed oscilloscope

The captured I/Q traces are processed using an offline DSP chain featuring:

• Resampling and normalization
• I/Q deskewing
• Blind CMA equalization
• Carrier-frequency-offset estimation
• Decision-Directed (DD) equalization
• Viterbi–Viterbi phase recovery

This platform allows us to study:

• Equalizer tap spread in strongly coupled channels
• Core-to-core mixing dynamics
• Capacity limits and mode-coupling statistics

These measurements are essential for validating theoretical models and for developing reduced-complexity DSP for RC-MCFs.

Distributed sensing techniques typically require high-power probe signals because backscattered reflections are extremely weak. However:

• High power causes nonlinear impairments and degrades data traffic
• Low power preserves data but yields poor sensing SNR unless heavy averaging is used

This trade-off limits simultaneous sensing and communication in standard fibers.

Together with our MATCH partners, we investigate whether the strong random coupling in RC-MCFs can provide:

• Enhanced sensitivity to environmental perturbations
• Access to distributed sensing information across multiple cores
• Sensing without compromising communication quality

This forms the basis for simultaneous high-speed transmission and distributed monitoring in the same fiber.

Through this project, INT aims to deliver:

• Experimental verification of high-speed coherent transmission in RC-MCFs
• Improved models of random mode coupling and its impact on DSP
• Demonstrations of joint communication and sensing in multicore fiber platforms
• Energy-efficient DSP algorithms optimized for strongly coupled SDM systems