Two-dimensional grating coupler on silicon with a high coupling efficiency and a low polarization-dependent loss

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Two-dimensional grating couplers are crucial for silicon photonic integrated circuits, enabling efficient light coupling between optical fibers and chip-based waveguides.
• Achieving high coupling efficiency while minimizing polarization-dependent loss (PDL) is essential for robust optical communication systems.

Purpose of the Study:

• To design and demonstrate a novel two-dimensional grating coupler with high coupling efficiency and low PDL.
• To reduce polarization-dependent loss using specific grating scatter and lattice structures.
• To enhance coupling loss performance with a metal mirror configuration.

Main Methods:

• Utilized two crossing ellipses as the grating scatter element.
• Employed a diamond-like grating lattice to minimize polarization-dependent loss.
• Integrated a metal mirror to further decrease coupling loss.

Main Results:

• Achieved a theoretical coupling loss of -1.73 dB at 1310 nm.
• Experimentally demonstrated a coupling loss of -2.37 dB with a 1 dB coupling bandwidth of 29 nm.
• Measured PDL below 0.2 dB over a 78 nm wavelength range.

Conclusions:

• The proposed 2D grating coupler effectively achieves high coupling efficiency and low PDL.
• The design, incorporating crossing ellipses and a metal mirror, offers a robust solution for silicon photonics.
• The configuration facilitates wafer-scale processing and simplified fiber alignment.