Water-Immersed GaP Huygens' Meta-Optics for Visible Structured Light Generation.

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Underwater photonics is crucial for biomedical imaging, analysis, and communication networks like the Internet of Underwater Things (IoUT).
• Structured light offers advanced capabilities for underwater sensing and signal transmission, but realizing compact, robust water-immersed photonic devices is difficult.
• Existing dielectric metasurfaces for underwater applications face challenges such as liquid instability, limited phase modulation, and sensitivity to fabrication errors.

Purpose of the Study:

• To demonstrate ultrathin, stable, water-immersed metasurfaces for generating structured light in the visible spectrum.
• To overcome the limitations of current underwater photonic devices by enhancing stability, fabrication tolerance, and phase modulation capabilities.

Main Methods:

• Fabrication of ultrathin metasurfaces using gallium phosphide (GaP) Huygens' integrated resonance units (HIRUs).
• Leveraging GaP's high refractive index and low optical loss.
• Integration of forward and inverse design strategies to achieve planar geometry and enhanced fabrication tolerance.

Main Results:

• Demonstration of stable, water-immersed GaP metasurfaces with planar geometry (approximately 1/5 of the operating wavelength).
• Metasurfaces exhibit enhanced fabrication tolerance and stable operation in liquid environments.
• Successful generation of various structured light beams in water, including abruptly autofocusing (AAF) beams, Bessel beams, optical vortices, and Gaussian focusing beams.

Conclusions:

• The developed GaP metasurfaces provide a scalable and reliable platform for underwater nanophotonics.
• This technology enables advanced underwater sensing, imaging, and communication for applications like the Internet of Underwater Things (IoUT).
• The study overcomes key challenges in realizing robust and efficient underwater photonic devices.