Maximizing Archimedes spiral packing density area.

Area of Science:

• Photonics
• Integrated Optics
• Waveguide Design

Background:

• Archimedes spiral delay lines are crucial for compact photonic integrated circuits.
• Achieving high packing density requires minimizing waveguide separation.
• Evanescent coupling in closely spaced waveguides can lead to unwanted resonance effects.

Purpose of the Study:

• To experimentally demonstrate a broadband Archimedes spiral delay line with high packing density on a silicon photonic platform.
• To investigate and mitigate resonance phenomena caused by evanescent coupling in spiral waveguides.
• To introduce a metric for evaluating the packing efficiency of spiral delay line designs.

Main Methods:

• Optimizing the gap between adjacent waveguides in the spiral configuration to sub-micron scales.
• Developing an analytical model for the resonance phenomenon in simple spirals.
• Minimizing resonance by ensuring different propagation constants (β) in adjacent waveguides.
• Fabricating and testing spiral waveguides with varying lengths and separation gaps.

Main Results:

• Demonstrated a broadband Archimedes spiral delay line with high packing density.
• Successfully mitigated resonance effects through careful waveguide design and propagation constant management.
• Introduced the Linear Density Figure of Merit (LDFM) to quantify packing efficiency.
• Achieved an optimal design with a length of 1.4mm occupying 60×60µm, yielding an LDFM of 388 km⁻¹.

Conclusions:

• High packing density in Archimedes spiral delay lines is achievable on silicon photonics.
• Controlling evanescent coupling and waveguide properties is key to mitigating resonance.
• The developed LDFM provides a valuable metric for comparing spiral delay line designs.