Holographic metasurface gas sensors for instantaneous visual alarms

Abstract

The rapid detection of biological and chemical substances in real time is particularly important for public health and environmental monitoring and in the military sector. If the process of substance detection to visual reporting can be implemented into a single miniaturized sensor, there could be a profound impact on practical applications. Here, we propose a compact sensor platform that integrates liquid crystals (LCs) and holographic metasurfaces to autonomously sense the existence of a volatile gas and provide an immediate visual holographic alarm. By combining the advantage of the rapid responses to gases realized by LCs with the compactness of holographic metasurfaces, we develop ultracompact gas sensors without additional complex instruments or machinery to report the visual information of gas detection. To prove the applicability of the compact sensors, we demonstrate a metasurface-integrated gas sensor on safety goggles via a one-step nanocasting process that is attachable to flat, curved, and flexible surfaces.

Pixelated bifunctional metasurface-driven dynamic vectorial holographic color prints for photonic security platform

“…The LC orientation changes induce an effective refractive index (∆ n eff ) shift; where n e and n o are the extraordinary and ordinary reflective index of the LCs, respectively, and θ = 0° represents the tangential orientation with respect to the rubbing direction. As a result, the LC cell can be used as a phase retarder where the phase retardation τ [rad] can be determined as where t is the thickness of the LC cell, and λ is the wavelength of the transmitted light 43 , 44 . The LC-integrated metasurface device is designed as to exhibit a specific polarization changing trajectory, when the light propagates through the LC medium (Fig.…”

“…Previously demonstrated dual-display devices that perform color printing and holography were limited to exhibiting only two pieces of information, whereas the device proposed here is able to produce fully polarized holographic images, so that much more information can be encoded into a single device. Furthermore, in order to simplify the polarization-sorting process with a simple application of electrical bias for the fully polarized holograms, a liquid crystal (LC) modulator is used instead of the combination of a polarizer and retarder 43 , 44 . This electrically tunable optical security platform aims to advance two-level encryption.…”

Geometric and physical configurations of meta‐atoms for advanced metasurface holography

“…Different geometries of meta‐atoms can be researched in innovative ways to produce multiplexed holography and dual‐mode metasurfaces. With the superior functionalities compared to conventional devices, metasurface holography will continue to mature and be able to produce real‐life applications 132–136 such as virtual/augmented reality devices, data storage, and security.…”

Chiroptical Metasurfaces: Principles, Classification, and Applications

“…Moreover, metasurfaces are much easier to fabricate due to their planar nature. To fully take advantage of metasurfaces, various applications have been studied, such as metaholograms [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ], metalenses [ 21 , 22 , 23 , 24 ], absorbers [ 25 , 26 , 27 ], structural colors [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], beam splitters [ 37 , 38 , 39 ], optical diodes [ 40 , 41 ], LiDAR applications [ 42 , 43 ], wide bandwith antennas [ 44 , 45 , 46 , 47 , 48 , 49 , 50 ], on-chip antennas [ 51 , 52 , 53 ], and MIMO and SAR antennas [ 54 , 55 , 56 ]. In particular, due to their ability to enhance chiral signals by field localization, chiral material sensing based on metasurfaces has sparked significant attention in recent years.…”