All-silicon nanorod-based Dammann gratings.

Area of Science:

• Optics and Photonics
• Nanotechnology
• Materials Science

Background:

• Established diffractive optical elements (DOEs) like Dammann gratings face fabrication complexity and performance trade-offs.
• Current methods for phase control in DOEs are often intricate and limit efficiency.

Purpose of the Study:

• To introduce a novel nanorod array-based Dammann grating design.
• To demonstrate efficient polarization conversion and phase modulation using nanorod orientation.
• To achieve high diffraction efficiencies for practical applications.

Main Methods:

• Combining geometric phase and depth-based phase modulation principles.
• Theoretical analysis and numerical simulations of nanorod arrays on silicon.
• Fabrication of nanorod-based Dammann gratings and characterization in the C-band.

Main Results:

• Nanorod arrays exhibit strong polarization conversion between circularly polarized states, acting as efficient half-wave plates.
• Phase control of circularly polarized light is achieved by tuning individual nanorod orientation angles.
• Nanorod-based Dammann gratings achieved diffraction efficiencies of 50%-52% in the 1530-1565 nm C-band.
• Uniform 4x4 spot arrays with a 59°x59° extending angle were generated.

Conclusions:

• Nanorod-based Dammann gratings offer a simplified, single-step fabrication process.
• Accurate phase control and strong polarization conversion enable high-performance optical elements.
• These gratings hold potential for diverse applications in optics and telecommunications.