Integer multi-wavelength gradient phase metagrating for perfect refraction: Phase choice freedom in supercella)

Area of Science:

• Acoustics
• Metamaterials
• Nanophotonics

Background:

• Phase gradient metagratings (PGMs) manipulate wavefronts using supercell phase increments and grating diffraction.
• Conventional PGMs are limited to single-frequency operation due to precise subcell resonance tuning.
• Existing designs focus on a 2π phase increment, neglecting broader phase choice possibilities.

Purpose of the Study:

• To overcome the single-frequency limitation of conventional PGMs.
• To explore the use of multi-2π phase increments in PGM supercells for multi-wavelength operation.
• To design and demonstrate a PGM capable of functioning at multiple wavelengths.

Main Methods:

• Investigated the freedom of phase choice within PGM supercells, specifically exploring multi-2π increments.
• Developed a collaborative mechanism involving surface impedance matching and multi-wavelength subcells.
• Designed and fabricated a supercell with eight curved pipes for two-wavelength operation.

Main Results:

• Achieved a linear adjacent phase gradient of 0.25π at 3430 Hz with near-perfect transmission due to impedance matching.
• Demonstrated consistent refraction direction at both the fundamental frequency (3430 Hz) and its double (6860 Hz).
• Validated the multi-wavelength functionality of the designed PGM.

Conclusions:

• The phase choice freedom in supercells enables the design of multi-wavelength PGMs.
• The proposed design strategy and experimental fabrication offer a pathway for advanced multi-wavelength metasurfaces and metagratings.
• This work expands the operational capabilities of PGMs beyond single-frequency applications.