Coherent few mode demultiplexer realized as a 2D grating coupler array in silicon

Area of Science:

• Photonics and Optical Communications
• Integrated Optics
• Silicon Photonics

Background:

• Few-mode fiber (FMF) enables higher data transmission capacity by supporting multiple spatial modes.
• Efficiently coupling and demultiplexing these modes on-chip is crucial for realizing FMF-based systems.
• Polarization multiplexing further enhances spectral efficiency, requiring advanced mode demultiplexing solutions.

Purpose of the Study:

• To demonstrate an on-chip coherent mode scrambling demultiplexer for polarization-multiplexed few-mode signals.
• To fabricate the device using a standard silicon-on-insulator (SOI) platform.
• To validate its performance in a few-mode division multiplexing transmission experiment.

Main Methods:

• Fabrication of a mode demultiplexer on a silicon-on-insulator platform.
• Integration of 2D grating couplers for dual-polarization few-mode fiber-to-chip coupling.
• Utilization of 4x4 multi-mode interferometers (MMIs) for optical hybrids.

Main Results:

• Achieved experimental peak coupling efficiencies of -5.2 dB (LP01) and -9.0 dB (LP11) at 1570 nm.
• Simulated coupling efficiencies of -3.6 dB (LP01) and -3.3 dB (LP11) at 1550 nm.
• Successfully performed a three LP mode division multiplexing transmission experiment with 32 Gbaud QPSK signals using offline MIMO digital signal processing (DSP).

Conclusions:

• The fabricated on-chip mode demultiplexer is effective for polarization-multiplexed few-mode signals.
• The device enables efficient fiber-to-chip coupling for different spatial modes.
• The results demonstrate the potential for advanced optical communication systems using silicon photonics.