Metamaterials for Analog Image Processing

A research team of Vanderbilt engineers that includes a scientist at Oak Ridge National Laboratory has demonstrated a new ultrathin filter, based on meta­materials, that allows for analog optical image processing. While digital image processing has become the prevailing technique in a variety of science and engineering disci­plines, it requires advanced computers, space to accommodate the computer, and substantial power.

Illustration: The metamaterial differentiates the object – the Vanderbilt logo –, resulting in the edges being selectively imaged. (Source: Vanderbilt U.)

“Most image processing is performed digitally, but optical analog processing has the advantages of being low power and high speed,” said Jason Valentine, associate professor of mechanical engineering and deputy director of the Vander­bilt Institute of Nanoscale Science and Engi­neering. While optical image processing has been performed in the past it generally requires multiple optical lenses resulting in a large system size. The meta­material filter, the first of its kind, differen­tiates the incoming light directly, allowing one to directly image the edges, or boundaries, of the object.

“Edge filtering is a common pre-processing step in object recog­nition, for instance, detecting the edge of a lane for autonomous vehicles. It can also be used for detecting margins of tumors in medical imagining or in classi­fying cell size and type in the case of cell sorting for cancer detection,” Valentine said. The metamaterial filter is based on a two-dimen­sional photonic crystal made from silicon that allows for direct imaging of the edges of an object in all directions. The nano­photonic differen­tiator can be integrated into an optical micro­scope or onto a camera sensor, easily adapting an existing image processing system.

“One of the primary benefits of our approach is the ability to integrate the meta­material with tradi­tional optical systems. As an example, we built an edge detection microscope by simply placing the meta­material filter within a commercial optical microscope,” said You Zhou, a Ph.D. student in the Inter­disciplinary Materials Science Program and one of the four authors. Testing included imaging the cells of onion epidermis, pumpkin stem and pig motor nerve.

The filter also was  integrated with a meta­material-based lens, resulting in a completely flat, and ultrathin optic that can perform edge imaging. This further reduces the size of traditional optical systems used for this purpose. “The key feature is the ability to perform image processing at the speed of light while requiring no input power and doing so in an extremely thin form factor,” Valentine said. “This opens new doors for real-time and high speed optical analog image proces­sing in applications such as machine vision and bio­logical imaging.”

Fabrication of the materials was performed in the Vander­bilt Institute of Nanoscale Science and Engineering and at the Center for Nano­phase Materials Sciences, a Science User Facility at the Oak Ridge National Labora­tory. Ivan Kravchenko, a physicist at ORNL, and Hanyu Zheng, a Ph.D. student in the Electrical Engi­neering Department at Vanderbilt, also are team members. (Source: Vanderbilt U.)

Reference: Y. Zhou et al.: Flat optics for image differentiation, Nat. Phot., online 24 February 2020, DOI: 10.1038/s41566-020-0591-3

Link: Interdisciplinary Materials Science Program, Vanderbilt University, Nashville, USA

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