Polarization-independent grating coupler for micrometric silicon rib waveguides

Area of Science:

• Photonics
• Integrated Optics
• Nanophotonics

Background:

• Grating couplers are essential for efficient fiber-chip coupling in photonic integrated circuits.
• Existing grating couplers exhibit strong polarization dependence, hindering dual-polarization applications.
• Silicon-on-insulator (SOI) technology is a leading platform for integrated photonics.

Purpose of the Study:

• To propose and demonstrate a polarization-independent grating coupler for thick rib SOI waveguides.
• To enhance the practical implementation of dual-polarization grating couplers.
• To achieve high coupling efficiency and directivity.

Main Methods:

• Design of grating pitch and duty cycle for polarization independence.
• Optimization without altering the bottom oxide thickness for simplified fabrication.
• Integration of a high reflectivity layer beneath the bottom oxide.
• Selective removal of the silicon substrate to enhance directivity.

Main Results:

• Demonstration of the first polarization-independent grating coupler for thick rib SOI waveguides.
• Achieved dual-polarization coupling efficiency of -2.8 dB.
• Simplified fabrication process by maintaining constant bottom oxide thickness.

Conclusions:

• The proposed grating coupler overcomes the polarization dependence limitations of conventional devices.
• This technology enables efficient dual-polarization fiber-chip coupling on SOI platforms.
• The simplified design facilitates practical integration into photonic systems.