High-efficiency, low-back-reflection, S+C+L band grating couplers compatible with silicon photonics MPW platforms

Area of Science:

• Photonics and Optical Engineering
• Semiconductor Device Fabrication
• Integrated Optics

Background:

• Grating couplers facilitate vertical optical fiber-to-chip connections, but often face bandwidth limitations.
• Silicon photonics multi-project wafer (MPW) platforms offer shallow etching processes that can be leveraged for advanced device design.
• Existing grating coupler designs may lack the bandwidth and fabrication tolerance required for emerging optical communication applications.

Purpose of the Study:

• To design and realize compact focusing grating couplers utilizing silicon photonics MPW platforms.
• To overcome the bandwidth limitations inherent in traditional grating coupler designs.
• To demonstrate high performance and fabrication tolerance for wafer-scale testing applications.

Main Methods:

• Employed an efficient semi-inverse design method to create two focusing grating couplers with minimum feature sizes of 100 and 200 nm.
• Utilized shallow etching processes available in silicon photonics MPW platforms.
• Fabricated devices using a 180-nm deep ultraviolet (DUV) MPW process.

Main Results:

• Achieved theoretical peak coupling efficiencies of -2.1 and -2.5 dB.
• Demonstrated coupling efficiencies greater than -12.4 and -13.3 dB across S-C-L bands.
• Fabricated devices exhibited coupling efficiency better than -10 dB over a 115.5 nm bandwidth.
• Observed coupling efficiency offsets within 1 dB for waveguide width deviations of ±20 nm within the C-band.

Conclusions:

• The developed grating couplers offer significant advantages in MPW compatibility, bandwidth, fabrication tolerance, and low back reflections.
• These devices are highly suitable for wafer-scale in-line testing of silicon photonic chips.
• The grating couplers hold potential for advanced S+C+L band optical communication systems.