Broad parameter optimization of polarization-diversity 2D grating couplers for silicon photonics

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Polarization-diversity couplers are vital for integrating optical fibers with silicon waveguides in all-optical circuits.
• Efficient coupling of unknown fiber polarization states to TE-polarized modes is a key challenge.

Purpose of the Study:

• To optimize a 2D photonic crystal grating for coupling single-mode telecom fibers to Silicon-on-Insulator (SOI) waveguides.
• To achieve high and polarization-independent coupling efficiency at 1550 nm.

Main Methods:

• Utilized a full 3D finite difference time domain (FDTD) calculation campaign for rigorous optimization.
• Investigated parameters including etch-depth, hole-radius, and grating-pitch.
• Employed guided-mode expansion to analyze photonic mode dispersion.

Main Results:

• Identified optimal photonic crystal grating parameters for enhanced performance.
• Achieved a mean polarization-averaged coupling efficiency of 48% (-3.2dB).
• Demonstrated marginal dependence on input fiber polarization (48 ± 3%).

Conclusions:

• The optimized grating design significantly improves coupling efficiency and polarization independence.
• 3D-FDTD simulations provide crucial insights into light coupling dynamics, aiding component design.
• The study suggests a resonant guided mode in the photonic crystal is responsible for efficient coupling, enabling faster optimization.