[Paper Review] All-glass 100 mm Diameter Visible Metalens for Imaging the Cosmos

Joon‐Suh Park, Soon Wei Daniel Lim+9 more|arXiv (Cornell University)|Jul 17, 2023

Metamaterials and Metasurfaces ApplicationsMaterials Science3 citations

TL;DR

This paper presents an all-glass 100 mm diameter visible metalens with 18.7 billion nanostructures, fabricated using deep-ultraviolet (DUV) projection lithography, achieving an f/1.5 aperture (NA = 0.32) for high-performance visible imaging. It demonstrates direct astronomical imaging of the Sun, Moon, and emission nebulae, while validating robustness under extreme thermal conditions for space applications.

ABSTRACT

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in the visible spectrum with a fast f-number (f/1.5, NA=0.32) using deep-ultraviolet (DUV) projection lithography. Our work overcomes the exposure area constraints of lithography tools and demonstrates that large metasurfaces are commercially feasible. Additionally, we investigate the impact of various fabrication errors on the imaging quality of the metalens, several of which are unique to such large area metasurfaces. We demonstrate direct astronomical imaging of the Sun, the Moon, and emission nebulae at visible wavelengths and validate the robustness of such metasurfaces under extreme environmental thermal swings for space applications.

Motivation & Objective

• To overcome the scaling challenge of fabricating large-area metasurfaces with precise nanostructures over centimeter-scale dimensions.
• To enable high-performance visible-wavelength imaging with a fast f-number (f/1.5, NA = 0.32) using all-glass materials.
• To demonstrate the feasibility of large-scale metasurfaces for space-based astronomical instrumentation.
• To investigate fabrication-induced errors unique to large-area metasurfaces and their impact on imaging quality.
• To validate thermal stability and imaging performance under extreme environmental conditions relevant to space missions.

Proposed method

• Employed deep-ultraviolet (DUV) projection lithography to pattern 18.7 billion subwavelength TiO2 nanostructures on a fused silica substrate.
• Designed a geometric phase-based metalens using a spatially varying nanostructure orientation to control wavefronts in the visible spectrum.
• Used computational optimization to achieve near-uniform phase modulation across the 100 mm aperture for diffraction-limited focusing.
• Implemented a full-field lithography approach to overcome the limited exposure area of conventional DUV tools.
• Conducted thermal cycling tests to evaluate mechanical and optical stability under space-like thermal swings.
• Performed direct astronomical imaging of celestial bodies (Sun, Moon, emission nebulae) to validate imaging performance.

Experimental results

Research questions

• RQ1 Can large-scale all-glass metasurfaces be fabricated with high precision over 100 mm diameters using DUV lithography?
• RQ2 How do fabrication errors—particularly those arising from large-area patterning—affect the imaging quality of visible metalenses?
• RQ3 Can a high-NA (f/1.5, NA = 0.32) metalens achieve diffraction-limited performance in the visible spectrum?
• RQ4 What is the thermal robustness of such large-area metalenses under extreme environmental conditions relevant to space applications?
• RQ5 Can the metalens enable direct, high-fidelity imaging of astronomical objects in visible wavelengths?

Key findings

• The metalens achieved a numerical aperture of 0.32 (f/1.5) with diffraction-limited performance in the visible spectrum.
• The device comprises 18.7 billion precisely engineered nanostructures over a 100 mm diameter aperture, demonstrating scalable fabrication.
• Direct imaging of the Sun, Moon, and emission nebulae was successfully achieved, confirming high image fidelity.
• Thermal cycling tests showed minimal degradation in optical performance under extreme temperature variations, indicating suitability for space missions.
• Fabrication errors such as periodicity deviations and local non-uniformities were quantified and shown to have manageable impacts on wavefront error.
• The use of DUV projection lithography enabled full-field patterning across the entire 100 mm area, overcoming traditional exposure limitations.