Conformable Holographic Metasurfaces

Chiral Metasurface Multifocal Lens in the Terahertz Band Based on Deep Learning

Chiral metasurfaces have garnered significant interest as an emerging field of metamaterials, primarily due to their exceptional capability to manipulate phase distributions at interfaces. However, the on-demand design of chiral metasurface structures remains a challenging task. To address this challenge, this paper introduces a deep learning-based network model for rapid calculation of chiral metasurface structure parameters. The network achieves a mean absolute error (MAE) of 0.025 and enables the design of chiral metasurface structures with a circular dichroism (CD) of 0.41 at a frequency of 1.169 THz. By changing the phase of the chiral metasurface, it is possible to produce not only a monofocal lens but also a multifocal lens. Well-designed chiral metasurface lenses allow us to control the number and position of focal points of the light field. This chiral metasurface, designed using deep learning, demonstrates great multifocal focus characteristics and holds great potential for a wide range of applications in sensing and holography.

On-Chip Optical Trapping with High NA Metasurfaces

Optical trapping of small particles typically requires the use of high NA microscope objectives. Photonic metasurfaces are an attractive alternative to create strongly focused beams for optical trapping applications in an integrated platform. Here, we report on the design, fabrication, and characterization of optical metasurfaces with a numerical aperture up to 1.2 and trapping stiffness greater than 400 pN/μm/W. We demonstrate that these metasurfaces perform as well as microscope objectives with the same numerical aperture. We systematically analyze the impact of the metasurface dimension on the trapping performance and show efficient trapping with metasurfaces with an area as small as 0.001 mm². Finally, we demonstrate the versatility of the platform by designing metasurfaces able to create multisite optical tweezers for the trapping of extended objects.

Two-tier manipulation of holographic information

Here we demonstrate the two-tier manipulation of holographic information using frequency-selective metasurfaces. Our results show that these devices can diffract light efficiently at designed frequency and environmental conditions. By changing the frequency and refractive index of the surrounding environment, the metasurfaces produce two different holographic images. We anticipate that these environmental dependent, frequency-selective metasurfaces will have practical applications in holographic encryption and sensing.

A Metasurface Beam Combiner Based on the Control of Angular Response

Beam combiners are widely used in various optical applications including optical communication and smart detection, which spatially overlap multiple input beams and integrate a output beam with higher intensity, multiple wavelengths, coherent phase, etc. Since conventional beam combiners consist of various optical components with different working principles depending on the properties of incident light, they are usually bulky and have certain restrictions on the incident light. In recent years, metasurfaces have received much attention and become a rapidly developing research field. Their novel mechanisms and flexible structural design provide a promising way to realize miniaturized and integrated components in optical systems. In this paper, we start from studying the ability of metasurfaces to manipulate the incident wavefront, and then propose a metasurface beam combiner in theory that generates an extraordinary refracted beam based on the principle of phase gradient metasurface. This metasurface combines two monochromatic light incidents at different angles with identical polarization but arbitrary amplitudes and initial phases. The combining efficiency, which is defined as the ratio of the power in the combining direction to the total incident power, is 42.4% at the working wavelength of 980 nm. The simulated results indicate that this proposed method is able to simplify the design of optical combiners, making them miniaturized and integrated for smart optical systems.

Non-Layered Gold-Silicon and All-Silicon Frequency-Selective Metasurfaces for Potential Mid-Infrared Sensing Applications

We report simulations on the spectral behavior of non-layered gold-silicon and all-silicon frequency-selective metasurfaces in an asymmetric element configuration in the mid-infrared spectral window of 5-5.8 μm. The non-layered layout is experimentally feasible due to recent technological advances such as nano-imprint and nano-stencil lithography, and the spectral window was chosen due to the multitude of applications in sensing and imaging. The architecture exhibits significant resonance in the window of interest as well as extended tunability by means of variation of cell element sizes and relative coordinates. The results indicate that the proposed metasurface architecture is a viable candidate for mid-infrared absorbers, sensors and imaging systems.

Generation of equine enteroids and enteroid-derived 2D monolayers that are responsive to microbial mimics

Enteroid cultures are three-dimensional in vitro models that reflect the cellular composition and architecture of the small intestine. One limitation with the enteroid conformation is the enclosed lumen, making it difficult to expose the apical surface of the epithelium to experimental treatments. The present study was therefore conducted to generate cultures of equine enteroids and to develop methods for culture of enteroid-derived cells on a two-dimensional plane, enabling easy access to the apical surface of the epithelium. Equine enteroids were established from small intestinal crypts within 7-9 days of culture. Transcriptional analysis of cell type markers confirmed the presence of enterocytes, stem-, Paneth-, proliferative-, enteroendocrine-, goblet- and tuft cells. This cellular composition was maintained over multiple passages, showing that the enteroids can be kept for prolonged periods. The transfer from 3D enteroids to 2D monolayers slightly modified the relative expression levels of the cell type markers, indicating a decrease of goblet- and Paneth cells in the monolayers. Stimulation with the TLR2, 3 and 4 agonists Pam3CSK4, Poly I:C and LPS, respectively, induced the pro-inflammatory cytokines TNF-α and IL-8, while the TLR5 agonist FliC only induced TNF-α. In addition, an up-regulation of TGF-β, IL-33 and IFN-β was recorded after exposure to lipofected Poly I:C that also affected the monolayer integrity. Thus, the equine enteroid-derived 2D monolayers described in the present study show both genetic and functional similarities with the equine intestine making it an interesting in vitro model for studies demanding access to the apical surface, e.g. in studies of host-microbe interactions.

Reconfigurable time-frequency division multiplexing metasurface: giving a helping hand to high signal-to-noise ratio and high data holographic imaging

A holographic imaging system based on reconfigurable time-frequency division multiplexing metasurface (RTFDMM) has been designed, in an attempt to address the problems of insufficient flexibility, low signal-to-noise ratio (SNR), and low data of traditional metasurface imaging devices. The modified Gerchberg-Saxton (MGS) algorithm in the front end of this system has been proposed to calculate the phase distribution required by the diffraction metasurface at the back end. The 1-bit low loss reconfigurable metasurface has been desiged in X-band. To obtain the best imaging results, the appropriate ranges of imazging distance, pixel size and resolution ratio are given by adjusting the phase distribution of metasurface. Based on the MGS algorithm and the 1-bit metasurface, the high-quality imaging system has been successfully established through the time-frequency division multiplexing (TFDM) technology. The high SNR imaging can be generated with the expansion of the time domain, while the high data imaging can be yielded with the quantization of the frequency domain. The proof-of-concept has demonstrated that the high data, high SNR, and high flexibility of the RTFDMM are critical technologies for the advancement of detection imaging equipment. Therefore, there are great possibilities for RTFDMM holographic imaging system to be applied in the intelligent detection platform in the future.

Programmable nonreciprocal meta-prism

Optical prisms are made of glass and map temporal frequencies into spatial frequencies by decomposing incident white light into its constituent colors and refract them into different directions. Conventional prisms suffer from their volumetric bulky and heavy structure and their material parameters are dictated by the Lorentz reciprocity theorem. Considering various applications of prisms in wave engineering and their growing applications in the invisible spectrum and antenna applications, there is a demand for compact apparatuses that are capable of providing prism functionality in a reconfigurable manner, with a nonreciprocal/reciprocal response. Here, we propose a nonreciprocal metasurface-based prism constituted of an array of phase- and amplitude-gradient frequency-dependent spatially variant radiating super-cells. In conventional optical prisms, nonreciprocal devices and metamaterials, the spatial decomposition and nonreciprocity functions are fixed and noneditable. Here, we present a programmable metasurface integrated with amplifiers to realize controllable nonreciprocal spatial decomposition, where each frequency component of the incident polychromatic wave can be transmitted under an arbitrary and programmable angle of transmission with a desired transmission gain. Such a polychromatic metasurface prism is constituted of frequency-dependent spatially variant transistor-based phase shifters and amplifiers for the spatial decomposition of the wave components. Interesting features include three-dimensional prism functionality with programmable angles of refraction, power amplification, and directive and diverse radiation beams. Furthermore, the metasurface prism can be digitally controlled via a field- programmable gate array (FPGA), making the metasurface a suitable solution for radars, holography applications, and wireless telecommunication systems.

Embedded Metal Oxide Plasmonics Using Local Plasma Oxidation of AZO for Planar Metasurfaces

New methods for achieving high-quality conducting oxide metasurfaces are of great importance for a range of emerging applications from infrared thermal control coatings to epsilon-near-zero nonlinear optics. This work demonstrates the viability of plasma patterning as a technique to selectively and locally modulate the carrier density in planar Al-doped ZnO (AZO) metasurfaces without any associated topographical surface profile. This technique stands in strong contrast to conventional physical patterning which results in nonplanar textured surfaces. The approach can open up a new route to form novel photonic devices with planar metasurfaces, for example, antireflective coatings and multi-layer devices. To demonstrate the performance of the carrier-modulated AZO metasurfaces, two types of devices are realized using the demonstrated plasma patterning. A metasurface optical solar reflector is shown to produce infrared emissivity equivalent to a conventional etched design. Second, a multiband metasurface is achieved by integrating a Au visible-range metasurface on top of the planar AZO infrared metasurface. Independent control of spectral bands without significant cross-talk between infrared and visible functionalities is achieved. Local carrier tuning of conducting oxide films offers a conceptually new approach for oxide-based photonics and nanoelectronics and opens up new routes for integrated planar metasurfaces in optical technology.

Metasurface-based contact lenses for color vision deficiency

We embed large-scale, plasmonic metasurfaces into off-the-shelf rigid gas permeable contact lenses and study their ability to serve as visual aids for color vision deficiency. In this study, we specifically address deuteranomaly, which is the most common class of color vision deficiency. This condition is caused by a redshift of the medium-type cone photoreceptor and leads to ambiguity in the color perception of red and green and their combinations. The effect of the metasurface-based contact lenses on the color perception was simulated using Commission Internationale de l'Eclairage (CIE) color spaces and conventional models of the human color-sensitive photoreceptors. Comparison between normal color vision and uncorrected and corrected deuteranomaly by the proposed element demonstrates the ability offered by the nanostructured contact lens to shift back incorrectly perceived pigments closer to the original pigments. The maximal improvement in the color perception error before and after the proposed correction for deuteranomaly is up to a factor of $\sim{10}$∼10. In addition, an Ishihara-based color test was also simulated, showing the contrast restoration achieved by the element, for deuteranomaly conditions.

Holography Using Curved Metasurfaces

In this work, we demonstrate nonflat metasurface holograms with applications in imaging, sensing, and anticounterfeiting. For these holograms, the image and its symmetry properties, with respect to the polarization of the light, depend on the specific shape of the substrate. Additionally, the sensitivity of the holographic image to the substrate shape can be engineered by distributing the phase information into determined areas of the metasurface.