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.
Figure 5. Operation of spin-encoded metaholograms in a broadband range of visible light. The metasurface optimized at 633 nm shows a negligible crosstalk between each image as shown in Figures 3 and 4. In other wavelengths, however, phase deviation (induced by propagation phase shift) causes crosstalk. Also, below 500 nm wavelength, extinction coefficient of a-Si:H is high enough to make the device lossy.
Symmetric spin–orbit interaction (SOI)‐based approaches apply a practical limit on helicity multiplexed metaoptics, i.e., center symmetric information encoding. Contrarily, asymmetric SOI's based on the combination of geometric and propagation phase‐delay approaches can effectively address such limitations for multifunctional multiplexed metaoptics on the cost of design complexities. In this paper, a simple asymmetric SOI‐based technique is realized for multifunctional metaoptics, employing only a single unit cell, breaking the conventional tradeoff between design complexity and efficient asymmetric transmission efficiency. The design approach depends on geometric phase alone, which eases the fabrication challenges and decreases the computational cost associated with previous asymmetric SOI‐based metaoptics. Furthermore, this study utilizes a new, low‐cost CMOS‐compatible material to optimize the proposed single unit cell for low loss and high transmission efficiency over the complete visible domain. On‐axis and off‐axis holographic metasurfaces are designed and integrated with pressure‐sensitive liquid crystal cells to demonstrate actively tunable metaholography with no limitation of center symmetric information encoding. The simple design technique, cost‐effective fabrication, and finger touch‐enabled holographic output switching make this integrated setup a potential candidate for many applications such as smart safety labeling, motion or touch recognition, and interactive displays for impact monitoring of precious artworks and products.
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