Efficient low-reflection fully etched vertical free-space grating couplers for suspended silicon photonics

Area of Science:

• Photonics and Optical Engineering
• Materials Science and Nanotechnology

Background:

• Efficient interfacing between integrated silicon photonics and free-space optics is essential for many applications.
• Existing methods often require complex fabrication processes or suffer from significant signal loss and reflection.

Purpose of the Study:

• To design and fabricate a grating coupler compatible with standard silicon photonics fabrication.
• To achieve simultaneous high transmission and low reflection for interfacing suspended silicon photonic membranes with free-space optics.

Main Methods:

• Utilized a two-dimensional shape-optimization followed by a three-dimensional parameterized extrusion for grating coupler design.
• Employed single-step lithography and etching in 220 nm silicon device layers for fabrication.
• Experimentally validated the design through optical characterization, enabling subtraction of other loss sources.

Main Results:

• The designed grating coupler targets -6.6 dB (21.8%) transmission and -27 dB (0.2%) reflection with a 75 nm bandwidth.
• Experimental validation yielded a measured transmission of 19% ± 2% and a reflection of 1.0% ± 0.8% with a 65 nm bandwidth.

Conclusions:

• The developed grating coupler offers a viable solution for efficient, low-loss interfacing between silicon photonic membranes and free-space optics.
• The design's compatibility with single-step fabrication processes makes it attractive for scalable photonic integrated circuit manufacturing.