High positional freedom SOI subwavelength grating coupler (SWG) for 300 mm foundry fabrication

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Nanofabrication

Background:

• Grating couplers are essential for interfacing optical fibers with integrated photonic circuits.
• Existing grating couplers often require precise alignment, increasing manufacturing and assembly costs.
• Subwavelength gratings (SWGs) offer design flexibility for improved performance.

Purpose of the Study:

• To design and fabricate a high-performance grating coupler with enhanced positional freedom.
• To achieve efficient coupling of 1550 nm TE-polarized light into silicon-on-insulator waveguides.
• To demonstrate a fabrication process compatible with standard CMOS technology.

Main Methods:

• Design of an apodized, single etch-step subwavelength grating (SWG) structure.
• Utilized a 220 nm silicon-on-insulator (SOI) platform with a 2μm buried oxide (BOX) layer.
• Fabrication in a 300 mm CMOS foundry.

Main Results:

• Achieved a maximum coupling efficiency of -7.49 dB (17.8%).
• Measured a -1 dB bandwidth of approximately 14 nm and a -3 dB bandwidth of 29.5 nm.
• Demonstrated a record -1 dB single mode fiber lateral alignment tolerance of 21.4 μm × 10.1 μm.

Conclusions:

• The developed SWG grating coupler offers a significant improvement in alignment tolerance for fiber-to-chip coupling.
• The high coupling efficiency and bandwidth make it suitable for various integrated photonic applications.
• CMOS-compatible fabrication enables scalable and cost-effective production.