Ultra-low-loss CMOS-compatible waveguide crossing arrays based on multimode Bloch waves and imaginary coupling

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Photonic integrated circuits (PICs) are crucial for modern communication and computing.
• Efficiently routing optical signals within PICs, especially at crossings, remains a significant challenge.
• Minimizing loss and crosstalk at waveguide crossings is essential for scaling PICs.

Purpose of the Study:

• To experimentally demonstrate a novel broadband waveguide crossing array design.
• To achieve ultralow loss and high crosstalk suppression in a CMOS-compatible geometry.
• To enable robust implementation of key components for dense photonic integration.

Main Methods:

• Fabrication of waveguide crossing arrays in a CMOS-compatible silicon-on-insulator (SOI) platform.
• Tailored excitation of a spatial Bloch wave by matching array periodicity to waveguide mode propagation constants.
• Experimental characterization of insertion loss and crosstalk performance across a broadband spectrum.

Main Results:

• Achieved an average ultralow insertion loss of 0.04 dB/crossing (0.9%), converging to 0.033 dB/crossing (0.075%).
• Demonstrated crosstalk suppression exceeding 35 dB.
• Validated the theoretical principle of operation involving Bloch wave excitation and radiative scattering.

Conclusions:

• The demonstrated waveguide crossing arrays offer a robust solution for dense photonic integration.
• The achieved performance metrics significantly advance the state-of-the-art in PIC components.
• This technology paves the way for more complex and efficient optical systems.