Inverse Design of Multi-Wavelength Achromatic Metalens Integrated On-Chip with Planar Waveguide

Area of Science:

• Photonics
• Nanotechnology
• Optical Engineering

Background:

• Waveguide-integrated metasurfaces are key for miniaturized on-chip optical systems.
• Achromatic metalenses are crucial for single-molecule fluorescence sensing, requiring high numerical aperture (NA) and consistent focal overlap across wavelengths.
• Designing multi-wavelength, high-NA integrated metalenses is challenging due to guided mode wavelength dependency.

Purpose of the Study:

• To present an inverse design framework for creating integrated achromatic metalenses.
• To achieve diffraction-limited focusing at three wavelengths with unity NA for enhanced optical sensing.
• To overcome the limitations of conventional designs in efficiency and sidelobe suppression.

Main Methods:

• Utilized an inverse design framework to optimize silicon nitride nanofin geometries and positions on a slab waveguide.
• Simultaneously optimized nanofin parameters for multi-wavelength focusing.
• Conducted numerical analysis to evaluate focusing performance and molecule detection efficiency.

Main Results:

• Achieved diffraction-limited focusing at three wavelengths with unity NA using the inverse-designed metalens.
• Demonstrated superior focusing efficiency and sidelobe suppression compared to conventional segmented designs.
• Showcased high molecule detection efficiency suitable for epi-fluorescence single-molecule sensing.

Conclusions:

• Inverse-designed metalenses offer a powerful platform for ultracompact on-chip optical systems.
• This approach enables efficient multi-wavelength focusing critical for advanced fluorescence spectroscopy and sensing.
• Highlights potential for applications in augmented reality, optical trapping, and other integrated photonic devices.