Nanometer-scale photon confinement in topology-optimized dielectric cavities

Area of Science:

• Nanophotonics and Materials Science
• Optical Engineering
• Additive Manufacturing

Background:

• Traditional nanophotonic device design relies on human intuition and basic optimization, limiting performance.
• Achieving strong light-matter interaction in nanophotonics is crucial for advanced optical devices.
• Fabrication constraints have historically posed challenges in realizing theoretically optimal nanophotonic designs.

Purpose of the Study:

• To integrate measured fabrication constraints into topology optimization for nanophotonic devices.
• To design and demonstrate a photonic nanocavity with maximized light-matter interaction.
• To achieve unprecedented performance metrics in terms of mode volume, quality factor, and footprint.

Main Methods:

• Utilized topology optimization incorporating measured fabrication constraints.
• Designed a compact silicon membrane photonic nanocavity for telecom wavelengths (λ ≈ 1550 nm).
• Fabricated the nanocavity using advanced nanofabrication techniques, achieving ultra-high aspect ratios (30) in 8 nm silicon bridges.
• Employed near-field optical measurements for experimental validation.

Main Results:

• Demonstrated an unprecedented photonic nanocavity with a mode volume of V ≈ 3 × 10⁻⁴ λ³, a quality factor Q ≈ 1100, and a footprint of 4 λ².
• Achieved experimental confirmation of photon confinement to a single hotspot, significantly below the diffraction limit in dielectric materials.
• Successfully fabricated structures with 8 nm silicon bridges and aspect ratios of 30.

Conclusions:

• The integrated framework of topology optimization and fabrication enables the design of high-performance nanophotonic devices.
• This approach overcomes previous limitations by accounting for real-world fabrication constraints.
• Initiates a new paradigm for high-performance additive and subtractive manufacturing in nanophotonics.