Session: Research Posters

Paper Number: 120289

120289 - From Leafhopper to Camouflage and Display 

Methods and media that enable camouflaging and displaying patterns by manipulating nano/microstructures set the foundations of data storage, display technology, anticounterfeiting and encryption. Enormous efforts have been put forward to address this challenge from the optical perspective. For example, metasurfaces and biomimicry optical gratings have been designed to tailor optical wavefronts to store images and videos. Information and images stored with these approaches are camouflaged in the sense that they cannot be directly retrieved by naked eyes (or with microscopes) but require illumination with specific wavelengths/polarizations or certain periods of ultraviolent exposure to be displayed. However, unlike the electronic approach like hard disk drives, where each bit can be simply chosen between states 0 and 1, the optical approaches rely on sophisticated ‘meta-atoms’, which are usually designed by Gerchberg-Saxton algorithm iteratively or by the point-source algorithm, to precisely alter the phase of wavefronts. Such a phase matching process requires these ‘meta-atoms’ to be individually designed, precisely fabricated, and illuminated by coherent or polarized light sources, for example lasers. Hence the fabrication capability limits such structures to be scaled up or down to fit different applications, and the availability of light sources constrains the working wavelengths. 

 

Here we design and demonstrate a pair of micro-sized pixel twins inspired by the leafhopper-produced brochosome structures - hollow spherical structures with distributed open pores bridging the inner and outer surfaces - to conceal binary data/images in visible range and display them in the infrared range via thermal excitation, which releases the constrains of external light sources. These brochosome-like pixel (BLP) twins are featured with either open pores (op-BLPs) or closed pores (cp-BLPs). We demonstrated that op-BLPs showed a 2.5 times stronger infrared emission capability compared to cp-BLPs, which enables them forming a binary 0-1 pair under thermal excitation. This allows us to display patterns/images binarily and retrieve under infrared cameras. At the same time, the BLPs share similar scattering behavior in visible range that ensures they are not easily distinguishable by human eyes, which serves as the camouflage mechanism. To our best knowledge, this is the first time that a pair of microscopic structures are designed to be distinguishable in the IR range but indistinguishable in the shorter visible range, even though the shorter wavelength provides a finer spatial resolution, according to the Rayleigh criterion.

 

Specifically, BLPs were modelled in SolidWorks, a computer-aided designing software, and the 3D models of BLPs are used in both the simulation and fabrication. The infrared emission and visible scattering behaviors of the BLPs were characterized respectively by their absorption cross sections and bi-directional scattering distribution functions and optimized through finite difference time domain simulations. Furthermore, BLP arrays of both kinds were fabricated through the two-photon polymerization 3D printing methods. The fabricated samples were examined under an infrared thermal mapping microscopy and a visible microscopy to verify their infrared contrast, as well as visible indistinguishability. Finally, as a proof of concept, QR codes arranged with the BLPs were fabricated to demonstrate the proposed visible camouflage and infrared display effect.

 

In conclusion, inspired by leafhopper-generated brochosomes, we have designed a pair of BLP twins with either open pores or closed pores to represent a pair of binary states in the infrared range but share similar appearances in visible range. Such a wavelength-dependent distinguishability of the two kinds of pixels sets the foundation for the visible camouflage and infrared display. Ultimately, the designed BLPs allow encoding of data in a pixel-by-pixel manner, and only require conventional thermal excitation for data extraction. This provides a new method of encrypted data storage or other technologies requiring selective visibility.

Presenting Author: Zhuo Li Carnegie Mellon University

Presenting Author Biography: Mr. Zhuo Li is currently a Ph.D. candidate in the Nano Energy Lab, at the Department of Mechanical Engineering, Carnegie Mellon University (CMU). Before joining CMU, he received the bachelor's degree in Physics (2019) form University of Chinese Academy of Sciences, Beijing, China. He also received the Master's degree in Mechanical Engineering (2021) from CMU on the way of persuing the Ph.D. degree. Zhuo has a board research interest in the optical and photonic disciplines, including optical active particle/surfaces, metasurfaces, thermal plasmonics, and infrared emission/detection in the nanoscale. His research extensively involves a variety of numerical techniques, including the finite-difference time-domain (FDTD) method and finite element method (FEM).

Authors:

Zhuo Li Carnegie Mellon University
Sheng Shen Carnegie Mellon University
Hyeong Seok Yun Carnegie Mellon University