Abstract
As the demand for secure digital data continues to increase, image encryption and decryption have recently received tremendous attention. The rapid development of ultrathin metasurfaces has mainly been driven by the desire for the introduction of novel methods with which electromagnetic waves can be manipulated. As a promising application of metasurfaces, metalenses have shown great potential to replace bulky traditional optical devices. In this work, we present that the images produced by a commercially available projector are encrypted by using the color superposition principle, and the fabricated metalens is subsequently utilized to perform image decryption with an incidence made of white light-emitting diodes (LEDs). The correct positions for image decryption are carefully found by three distinct diode lasers as incident light sources. Recent investigations show that high-performance metalenses can be successfully developed once the suitable dielectric material is chosen. As a consequence, our metalens of high performance is composed of hexagon-resonated elements (HREs) made of gallium nitride (GaN) and is capable of resolving line width as small as 870 nm. The metalens with a smaller diameter of 8 μm is numerically simulated with a diffraction-limited focusing efficiency as high as 92%. This work once again shows that GaN metalenses, as future optics, have great prospects in expanding widespread applications in the near future.
Highlights
As the largest system in the human brain, the visual cortex is devoted to the processing of perceived visual images
We have successfully demonstrated images decrypted by the fabricated metalens
The encrypted images can be clearly observed at appropriate z-axis positions, which are carefully inspected by using the lasers as incident light sources
Summary
As the largest system in the human brain, the visual cortex is devoted to the processing of perceived visual images. To realize strong transmission efficiency, dielectric materials have been introduced as being the sub-wavelength building blocks for the fabrication of metasurfaces. In 2017, Chen et al [23] firstly fabricated GaN metalenses capable of on- and off-axis focusing of diffraction limit by using the Pancharatnam–Berry (PB) phase design principle and proposed its feasible application in CMOS image sensor. An integrated-resonant unit element (IRUE) with the PB phase rotational morphology was utilized to construct an achromatic GaN metalens that can continuously eliminate wavelength aberration in the visible spectrum [28]. We have prepared a GaN metalens built up with high-aspect-ratio HREs to perform the capability of encryption and decryption of digital images produced by a projector with white light-emitting diodes (LEDs) as a light source. The diffraction-limited focusing and 1951 United States Air Force (USAF) imaging capacities for the 450-nm-design metalens are sequentially displayed in this work
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