Far-field sub-diffraction focusing lens based on binary amplitude-phase mask for linearly polarized light

Area of Science:

• Photonics
• Optics
• Nanotechnology

Background:

• Planar lenses offer miniaturization and integration advantages in photonic devices.
• Traditional planar lenses are limited by the diffraction limit, hindering sub-diffraction focusing.
• Super-oscillation offers sub-diffraction focusing but suffers from large sidelobes, limiting applications.

Purpose of the Study:

• To demonstrate a far-field sub-diffraction planar lens with a binary amplitude-phase mask.
• To overcome the limitations of sidelobes and field of view in super-oscillation lenses.
• To achieve long focal length and sub-diffraction focusing with a planar lens design.

Main Methods:

• Design and fabrication of a binary amplitude-phase mask for a planar lens.
• Illumination of the lens with a linearly polarized plane wave at a wavelength of 632.8 nm.
• Characterization of the focal spot size, focal length, and sidelobe levels.

Main Results:

• A long focal length of 148λ (94 µm) was achieved.
• A super-oscillatory focal line width of 0.406λ (full width at half maximum) was realized.
• The planar lens exhibited small sidelobes (max < 22% of central peak) and a wide field of view.

Conclusions:

• The demonstrated binary amplitude-phase planar lens successfully achieves far-field sub-diffraction focusing.
• This design overcomes the significant sidelobe issue associated with super-oscillation, enabling practical applications.
• The approach is extendable to other spectral ranges for long focal length sub-diffraction focusing.