Visible and near-infrared programmable multi-level diffractive lenses with phase change material Sb₂S₃

Area of Science:

• Optics and Photonics
• Materials Science

Background:

• Flat programmable multi-level diffractive lenses (PMDL) offer advanced optical functionalities.
• Phase change materials (PCMs) are explored for reconfigurable optical devices.
• Sb2S3 exhibits a high refractive index contrast (Δn ∼ 0.6) between amorphous and crystalline states, with low losses in the near-infrared.

Purpose of the Study:

• To investigate the feasibility of Sb2S3-based PMDLs for tunable focusing in the near-infrared and visible spectrum.
• To explore the performance of these lenses at short wavelengths (down to 450 nm), an area not previously studied for reconfigurable PCMs.
• To demonstrate the potential of Sb2S3 as a material for advanced reconfigurable optical devices.

Main Methods:

• Fabrication of PMDLs using Sb2S3 concentric rings with optimized heights embedded in a glass substrate.
• Utilized a modified direct binary search algorithm for optimizing ring heights.
• Characterized lens performance across near-infrared (850 nm) and visible (450 nm) wavelengths.

Main Results:

• Demonstrated effective focus shifting by altering the phase of Sb2S3 between amorphous and crystalline states.
• Achieved good performance in the visible band despite potential losses, due to thin lens designs (∼ 1.5λ to 3λ).
• Successfully designed PMDLs operating at wavelengths from 850 nm to 450 nm.

Conclusions:

• Sb2S3 is a promising material for realizing programmable lenses across a broad spectral range, including short visible wavelengths.
• The developed PMDLs are polarization-insensitive and suitable for applications in dual-functionality devices, optical imaging, and biomedical science.
• This research expands the application scope of phase change materials in optics.