Multi-NA Metalens Array for Compact High-NA Microscopy

TL;DR

This work addresses compact, high-NA fluorescence microscopy in the visible range using CMOS-compatible metalenses. It introduces a three-element, co-planar silicon-rich nitride metalens array designed for a wavelength of about 660 nm with NA values of 0.54, 0.92, and 0.97, enabling within-sample NA benchmarking without objective swaps. The design uses a locally periodic approximation to select unit cells from a library and realize a non-paraxial focusing phase while maintaining high transmission. Fabrication on 4-inch wafers with a 600 nm SRN layer is CMOS-friendly and scalable, enabling wafer-level integration with image sensors. Experimental validation includes diffraction-limited focusing and AF647 ZO-1 imaging of annular cell monolayers, demonstrating NA-dependent sharpening and practical viability for compact bioimaging.

Abstract

We demonstrate a CMOS-compatible silicon-rich nitride metalens array for visible microscopy at 660 nm. Three co-planar elements provide numerical apertures of 0.54, 0.92, and 0.97, enabling within-sample NA benchmarking without objective swaps. Imaging of annular cell monolayers labeled in the AF647 ZO-1 channel shows progressive sharpening of junctional edges and reduced blur with increasing NA, consistent with diffraction-limited scaling. The compact, planar platform supports direct integration with image sensors, offering a practical route to high-NA fluorescence bioimaging in space-constrained, low-cost systems.

Figures (4)

• Figure 1: (a) Woollam ellipsometry showing SRN $n$ (solid) and $k$ (dashed) for recipes R1--R10 on fused silica. (b) Transmission map at $660\,\mathrm{nm}$ for the chosen recipe. (c) Phase $\phi$ at $660\,\mathrm{nm}$ over the same design space. (d) Unit cell with SRN pillar of width $W$, length $L$, height $H$, and pitch $P$; lateral sizes $W,L\in[150\text{--}340]\,\mathrm{nm}$.
• Figure 2: (a) Fabricated metalens chip held by a tweezer; the array location is circled. (b) Optical micrographs of fabricated metalenses on the substrate. (c) SEM of the central lens region resolving the meta-atom lattice (scale bar 5 µm). (d) Wider-area SEM of the array (scale bar 10 µm).
• Figure 3: (a) Overview of the imaging setup. (b) Normalized intensity profiles at focus for NA 0.54, 0.92, and 0.97, showing a narrower main lobe with increasing NA. (c–e) Imaging of a USAF 1951 high-resolution target through the metalens array at different numerical apertures. Higher NA yields crisper group elements and resolves the “2” feature more distinctly. (f) Imaging of a test logo for qualitative verification of NA 0.54 lens.
• Figure 4: (a) Bench setup with the metalens array between relay objectives. (b) Annular cell monolayers on coverslips prior to fluorescence imaging. (c) AF647 ZO-1 fluorescence of the annular ring acquired with the NA 0.54 metalens. (d) Single-cell AF647 ZO-1 fluorescence acquired with the NA 0.92 metalens. (e) Single-cell AF647 ZO-1 fluorescence acquired with the NA 0.97 metalens, showing the highest junctional edge clarity.