Asymmetric metasurface photodetectors for single-shot quantitative phase imaging

TL;DR

This paper introduces asymmetric metasurface photodetectors that enable single-shot quantitative phase imaging without complex optical setups, offering a compact and efficient solution for biomedical and surface profiling applications.

Contribution

The work presents a novel angle-sensitive photodetector design using plasmonic metasurfaces, allowing direct phase object visualization and single-shot quantitative phase imaging.

Findings

Achieved phase contrast detection below 10 mrad.

Demonstrated angle-sensitive responsivity with metasurface-coated photodetectors.

Enabled single-shot quantitative phase imaging with a custom reconstruction algorithm.

Abstract

The visualization of pure phase objects by wavefront sensing has important applications ranging from surface profiling to biomedical microscopy, and generally requires bulky and complicated setups involving optical spatial filtering, interferometry, or structured illumination. Here we introduce a new type of image sensors that are uniquely sensitive to the local direction of light propagation, based on standard photodetectors coated with a specially designed plasmonic metasurface that creates an asymmetric dependence of responsivity on angle of incidence around the surface normal. The metasurface design, fabrication, and angle-sensitive operation are demonstrated using a simple photoconductive detector platform. The measurement results, combined with computational imaging calculations, are then used to show that a standard camera or microscope based on these metasurface pixels can directly visualize phase objects without any additional optical elements, with state-of-the-art minimum detectable phase contrasts below 10 mrad. Furthermore, the combination of sensors with equal and opposite angular response on the same pixel array can be used to perform quantitative phase imaging in a single shot, with a customized reconstruction algorithm which is also developed in this work. By virtue of its system miniaturization and measurement simplicity, the phase imaging approach enabled by these devices is particularly significant for applications involving space-constrained and portable setups (such as point-of-care imaging and endoscopy) and measurements involving freely moving objects.