A Semisolid Micromechanical Beam Steering System Based on Micrometa-Lens Arrays

Perfect anomalous refraction metasurfaces empowered half-space optical beam scanning

Metasurface-based optical beam scanning devices are gaining attention in optics and photonics for their potential to revolutionize light detection and ranging systems. However, achieving anomalous refraction with perfect efficiency (>99%) remains challenging, limiting the efficiency and field of view (FOV) of metasurface-based optical beam scanning devices. Here, we introduce a paradigm for achieving perfect anomalous refraction by augmenting longitudinal degrees of freedom arousing a multiple scattering process to optimize symmetry breaking. An all-dielectric quasi-three-dimensional subwavelength structure (Q3D-SWS), composed of a purposely designed multilayer film and a dielectric metasurface separated by a spacer, is proposed to eliminate reflection loss and spurious diffraction, achieving >99% anomalous refraction efficiency. By independently rotating two cascaded Q3D-SWSs, we experimentally showcase half-space optical beam scanning, achieving a FOV of 144° × 144°, with a maximum efficiency exceeding 86%. Our results open new avenues for high-efficiency metasurfaces and advances applications in light detection and ranging systems.

Polarization-controlled metasurface for simultaneous holographic display and three-dimensional depth perception

Simultaneous optical display and depth perception are crucial in many intelligent technologies but are usually realized by separate bulky systems unfriendly to integration. Metasurfaces, artificial two-dimensional optical surfaces with strong light-matter interaction capabilities at deep subwavelength scales, offer a promising approach for manufacturing highly integrated optical devices performing various complex functions. In this work, we report a polarization-multiplexed metasurface that can functionally switch between holographic display and Dammann gratings. By tailoring the incidence polarization, the metasurface can display high-quality holographic images in the Fresnel region or project a uniform spot cloud nearly covering the entire 180° × 180° transmissive space. For the latter, a projection and three-dimensional (3D) reconstruction experiment is conducted to elaborate the potential in retrieving 3D complex spatial information. The current results provide a prominent way to manufacture lightweight and highly-integrated comprehensive imaging systems especially vital for cutting-edge intelligent visual technologies.

A Review of Cascaded Metasurfaces for Advanced Integrated Devices

This paper reviews the field of cascaded metasurfaces, which are advanced optical devices formed by stacking or serially arranging multiple metasurface layers. These structures leverage near-field and far-field electromagnetic (EM) coupling mechanisms to enhance functionalities beyond single-layer metasurfaces. This review comprehensively discusses the physical principles, design methodologies, and applications of cascaded metasurfaces, focusing on both static and dynamic configurations. Near-field-coupled structures create new resonant modes through strong EM interactions, allowing for efficient control of light properties like phase, polarization, and wave propagation. Far-field coupling, achieved through greater interlayer spacing, enables traditional optical methods for design, expanding applications to aberration correction, spectrometers, and retroreflectors. Dynamic configurations include tunable devices that adjust their optical characteristics through mechanical motion, making them valuable for applications in beam steering, varifocal lenses, and holography. This paper concludes with insights into the potential of cascaded metasurfaces to create multifunctional, compact optical systems, setting the stage for future innovations in miniaturized and integrated optical devices.

Dielectric Liquid Microlens Array with Tunable Focal Length Based on Microdroplet Array Created via Dip-Coating Method

A dielectric liquid microlens array (LMA) with a tunable focal length was fabricated by using a microdroplet array generated through the dip-coating method. The process began with treating the octadecyltrichlorosilane (OTS) layer with selective UV/O3 irradiation for 20 min to establish a hydrophilic-hydrophobic patterning surface. The substrate was subsequently immersed in glycerol and then withdrawn at a constant rate to create a microdroplet array. Upon filling the cell with matching oil (SL5267) and placing it within a square array of a 200 μm diameter glycerol microdroplet array, the LMA was produced. The focal length ranged from approximately -0.96 to -0.3 mm within a voltage range of 0 to 60 Vrms. The glycerol microdroplets, characterized by their shapes, sizes, curvatures, and filling factors, can be precisely controlled by designing an OTS patterning or adjusting the dip-coating speed. This approach offers a rapid and high-throughput method for preparation. Our approach to fabricating tunable LMA offers several advantages, including simplicity of fabrication, uniform structural properties, cost-effectiveness, polarization independence, and excellent optical performance. These focus-tunable LMAs hold significant potential for applications in image processing, 3D displays, medical endoscopy, and military technologies.

An ultra-fast method for designing holographic phase shifting surfaces

Holographic phase-shifting surfaces (PSSs) have been proven to offer a cost-effective solution for enabling passive arrays to mechanically steer their beams toward desired directions. However, even though the principle of operation of PSSs is straightforward, designing a PSS is very challenging, because it involves an extremely high computational time, which in turn limits their usage and development. Notably, traditional design approaches of PSSs, with N number of layers that have M different variations of conductive patches, need [Formula: see text] full-wave simulations to be properly characterized. To address these challenges that are associated with the design of PSSs and reduce the needed computational effort, we present here a semi-numerical approach that enables the efficient design of holographic PSSs. Specifically, by representing an N-layer PSS unit-cell as N cascaded networks, where each network represents one layer of the PSS that has M different designs of sub-wavelength resonators, we only need to conduct [Formula: see text] full-wave simulations to collect all the required data needed to analyze the performance of the PSS. In turn, by utilizing the multiplication property of ABCD parameters we can evaluate very efficiently all the [Formula: see text] different combinations that characterize our PSS. To validate the accuracy of our design methodology, a 1-D beam steerable antenna system is designed that is comprised of a circularly polarized holographic metasurface antenna (HMA) and a hybrid PSS, both operating at 30 GHz. Comparisons between our semi-numerical results, full-wave simulations, and measurements demonstrate an angular error of less than [Formula: see text].

Large-Area and Rapid Fabrication of a Microlens Array on a Flexible Substrate for an Integral Imaging 3D Display

A curved integral imaging three-dimensional (3D) display attracts a lot of interest due to its enhanced 3D sense of immersion and wider viewing angle. In this paper, a microlens array (MLA) based on a flexible poly(ethylene terephthalate) (PET) substrate was achieved by a straightforward, rapid, and low-cost technique. The reactive ion etching (RIE) process treated PET/CYTOP covered with a flexible mask to generate a hydrophilic-hydrophobic patterned surface. The well-designed arrays of confined adhesive droplets with a controlled geometry on a hydrophilic-hydrophobic patterned surface were formed using the blade-coating method. A flexible MLA with a diameter of 820 μm, a size of 5.3 cm × 5.1 cm, and a radius of curvature of 25 cm was fabricated and combined with a curved two-dimensional (2D) monitor to realize a lateral viewing range of 6.4 cm at a viewing distance of 25 cm, which is 4 times larger than with flat integral imaging 3D display system. The flexible MLA has the advantages of a controllable lens profile and large pitch, and it can be manufactured on a large scale. In addition, it provides a large viewing angle for the reconstructed 3D image.