Dimensional variation tolerant silicon-on-insulator directional couplers

Area of Science:

• Photonics and optical engineering
• Integrated optics
• Semiconductor device fabrication

Background:

• Silicon photonics manufacturing processes are susceptible to variations in critical dimensions.
• These variations impact the performance of integrated optical devices, such as directional couplers.
• Existing directional coupler designs often exhibit significant performance deviations due to fabrication tolerances.

Purpose of the Study:

• To design silicon ridge/rib waveguide directional couplers with enhanced tolerance to fabrication variations.
• To quantify the improvement in splitting ratio stability compared to conventional designs.
• To evaluate the broadband performance and spectral dependence of the variation-tolerant couplers.

Main Methods:

• Design of silicon ridge/rib waveguide directional couplers.
• Fabrication using the IMEC Standard Passives process.
• Wafer-scale measurements to assess performance variations.
• Analysis of normalized standard deviation in the per-length coupling coefficient.

Main Results:

• The variation-tolerant directional couplers exhibit a normalized standard deviation in the coupling coefficient up to 4 times smaller than strip waveguide designs.
• These couplers demonstrate superior broadband performance.
• The deviation in the coupling coefficient shows the lowest spectral dependence among the tested designs.

Conclusions:

• Silicon ridge/rib waveguide directional couplers can be designed for simultaneous tolerance to multiple fabrication variations.
• The developed designs offer significant improvements in splitting ratio stability and spectral performance.
• This advancement is crucial for reliable and high-performance silicon photonic integrated circuits.