Ultra-compact bent multimode silicon waveguide with ultralow inter-mode crosstalk.

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Multimode waveguides are crucial for integrated photonics.
• Achieving sharp bends in silicon waveguides without performance degradation is challenging.
• Existing solutions for sharp bends often require larger footprints.

Purpose of the Study:

• To propose and demonstrate a sharply bent multimode silicon waveguide.
• To achieve low insertion loss and inter-mode crosstalk in a compact waveguide bend.
• To utilize mode converters and particle swarm optimization for waveguide geometry engineering.

Main Methods:

• Designing a sharply bent multimode silicon waveguide using mode converters.
• Employing particle swarm optimization to optimize the waveguide geometry.
• Fabricating the device on a silicon-on-insulator platform using standard lithography and etching.
• Experimentally characterizing the waveguide bend's performance, including insertion loss and inter-mode crosstalk.

Main Results:

• Demonstrated a sharply bent multimode silicon waveguide with a 5 μm bend radius.
• Achieved insertion loss below 0.2 dB and inter-mode crosstalk below -22 dB across the 1500-1600 nm wavelength range.
• Obtained performance comparable to conventional schemes with a 40 μm bend radius.
• Fabrication required only one lithography/etching step without additional processes.

Conclusions:

• The proposed mode converter-based multimode bend offers a highly efficient solution for compact silicon photonic circuits.
• This approach significantly reduces the footprint of waveguide bends while maintaining excellent optical performance.
• The demonstrated technology is compatible with standard silicon photonics fabrication, paving the way for miniaturized optical devices.