Metasurfaces perform all-optical image edge detection
Being passive devices, such “computing metasurfaces” perform the mathematical operations without requiring any power, hence they could dramatically slash the power consumption of object recognition systems where edge detection is a pre-requisite. In a paper titled “High-Index Dielectric Metasurfaces Performing Mathematical Operations” published in the Nano Letters, the researchers demonstrate optical metasurfaces composed of dielectric nanobeams, illuminated by light polarized along the beams’ direction.
(right) derivative image of AMOLF logo taken at a wavelength
of 726nm. Credit: AMOLF
When an image is projected onto the transparent metasurface, the transmitted light forms a new image that shows the edges of the original. Effectively, the metasurface performs a mathematical derivative operation on the image which provides a direct probe of edges in the image.
Typically, this edge detection is performed in the digital domain on images captured by a sensor, requiring extra computing steps and implying fundamental speed limitations and high energy consumption. Here, the optical mathematical transformation results from the fact that each spatial frequency that composes the image has a tailored transmission coefficient through the metasurface. This tailored transmission is the result of a complex interference of light as it propagates through the metasurface.
The authors anticipate that such transparent computing metasurfaces could be integrated at sensor level, directly onto a standard CCD or CMOS detector chip to boost the speed of existing imaging processing techniques and lower energy usage, for ultrafast object detection in augmented reality applications.
AMOLF – https://amolf.nl
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