Intensity-asymmetric wavefront shaping in nonlocal meta-lens

Area of Science:

• Photonics and optical engineering
• Materials science
• Nonlinear optics

Background:

• Asymmetric wavefront shaping is crucial for advanced photonic functionalities like unidirectional transmission and nonreciprocal light control.
• Achieving these functionalities in passive nonlinear metasurfaces is challenging due to trade-offs in nonlinear efficiency, phase modulation, and directional asymmetry, especially on low-index substrates.

Purpose of the Study:

• To propose and demonstrate a novel meta-lens design for effective asymmetric wavefront shaping.
• To overcome the limitations of existing metasurfaces by integrating local and nonlocal resonances.
• To achieve strong directional response and high nonlinear efficiency on low-index substrates.

Main Methods:

• A hybrid meta-lens design integrating local Mie-type resonances with nonlocal quasi-bound states in the continuum.
• Utilizing substrate-induced asymmetry without additional layers.
• Experimental characterization of directional focusing at fundamental, second, and third harmonic wavelengths.

Main Results:

• The proposed meta-lens exhibits a strong directional response originating from silica substrate-induced asymmetries.
• High nonlinear efficiency and robust phase modulation are preserved.
• A maximum forward-to-backward power ratio exceeding 10 dB was experimentally demonstrated for directional focusing.

Conclusions:

• The developed hybrid meta-lens effectively achieves asymmetric wavefront shaping and nonreciprocal light control.
• This design offers a pathway to overcome existing trade-offs in metasurface functionalities.
• The work presents new opportunities for applications in nonreciprocal LIDAR and optical computing.