Very sharp adiabatic bends based on an inverse design

Area of Science:

• Photonics and optical engineering
• Metamaterials and nanophotonics

Background:

• Adiabatic optical wave propagation is crucial for integrated photonic circuits.
• Achieving sharp bends in multimode waveguides with low loss and high mode selectivity is challenging.
• Existing waveguide designs often require large footprints, limiting miniaturization.

Purpose of the Study:

• To demonstrate ultra-sharp 90° micro-bends for adiabatic optical wave propagation in multimode waveguides.
• To design and fabricate compact bending structures using inverse design and digital waveguide metastructures.
• To achieve low insertion loss and high suppression ratios for the fundamental mode.

Main Methods:

• Utilized an inverse design method to create novel waveguide metastructures.
• Fabricated the designed micro-bend structures on a silicon-on-insulator (SOI) platform.
• Characterized the optical performance, including transmission loss and mode suppression, via experimental measurements and numerical simulations.

Main Results:

• Demonstrated 90° micro-bends with footprints as small as 2.6 μm × 2.6 μm.
• Achieved low insertion loss of ~1 dB for the TE00 mode in 2 μm wide waveguides with 1 μm bending radii.
• Obtained a suppression ratio of >20 dB for higher-order modes.
• Measured transmission spectra consistent with numerical simulations over a 40 nm bandwidth.

Conclusions:

• The inverse design method successfully created compact and efficient micro-bend structures for optical waveguides.
• These digital waveguide metastructures enable adiabatic wave propagation around sharp corners with excellent mode control.
• The fabricated devices show great potential for miniaturizing integrated photonic circuits and advanced optical systems.