High-efficiency vertically emitting coupler facilitated by three wave interaction gratings.

Area of Science:

• Integrated Photonics
• Nanophotonics
• Semiconductor Devices

Background:

• Efficient light coupling into photonic integrated circuits is crucial for device performance.
• Traditional grating couplers often require complex structures like bottom reflectors or multiple material layers, increasing fabrication complexity and cost.
• Standard silicon-on-insulator (SOI) technology is widely used, but maximizing coupling efficiency within its constraints remains a challenge.

Purpose of the Study:

• To design and numerically demonstrate a grating coupler with near-unity coupling efficiency for normal incidence.
• To achieve high performance using standard 220-nm-thick SOI technology with simplified fabrication processes.
• To optimize the grating coupler's spectral characteristics, balancing peak efficiency and bandwidth.

Main Methods:

• Designed a grating coupler utilizing three scattering sites per local period to break vertical symmetry.
• Employed adjoint method-based optimization to engineer the coupling spectrum and efficiency.
• Simulated device performance using standard 220-nm-thick SOI fabrication parameters, requiring only two lithography masks.

Main Results:

• Achieved near-unity coupling efficiencies ranging from 93.4% (-0.3 dB) to 98.6% (-0.06 dB).
• Demonstrated 1 dB bandwidths between 8 nm and 48 nm, centered at 1.55 µm.
• The design eliminates the need for bottom reflectors or additional layers, simplifying fabrication.

Conclusions:

• The proposed grating coupler design offers a significant advancement in silicon photonics, enabling highly efficient light coupling.
• The simplified fabrication process using only two masks makes it compatible with standard SOI manufacturing.
• This approach provides a viable solution for high-performance photonic integrated circuits requiring efficient light input.