Metallic planar lens constructed by double-turn waveguides for sub-diffraction-limit focusing

Area of Science:

• Plasmonics
• Nanophotonics
• Metamaterials

Background:

• Sub-diffraction-limit focusing is crucial for advanced imaging and lithography.
• Existing methods often face challenges with fabrication complexity and resolution limits.

Purpose of the Study:

• To conceptually demonstrate a metallic planar lens capable of sub-diffraction-limit focusing.
• To investigate the use of double-turn waveguides for precise phase modulation.
• To achieve enhanced resolution beyond the conventional diffraction limit.

Main Methods:

• Utilizing surface plasmon polaritons (SPPs) propagating in metal-insulator-metal (MIM) waveguides.
• Employing the finite-difference time-domain (FDTD) numerical method to analyze waveguide parameters and phase delay.
• Designing a planar lens structure with double-turn waveguides for spatial phase modulation.

Main Results:

• Achieved a focal length in agreement with theoretical design.
• Obtained a full-width at half-maximum (FWHM) of 0.446λ, surpassing the diffraction limit.
• Demonstrated robustness of superfocusing performance against minor structural variations.
• Reduced the aspect ratio of nanoslits to 3.33, simplifying fabrication.

Conclusions:

• The proposed metallic planar lens offers a viable approach for super-resolution imaging.
• The design's robustness and simplified fabrication make it suitable for practical applications.
• Potential applications include lithography, integrated optics, and advanced microscopy.