Mold-free self-assembled scalable microlens arrays with ultrasmooth surface and record-high resolution

Achieving precise dual-modulation of polarization and phase using a broadband terahertz single-cell metasurface

This paper proposes a reflective metasurface composed of a single unit structure, yet capable of achieving precise control of two degrees of freedom. By grooving two orthogonal slots on the copper ring, it enables the independent conversion of the two orthogonal components of the incident waves. Consequently, incident linearly-polarized waves can be rotated by an arbitrary angle. For circularly-polarized waves, the handedness will be reversed; furthermore, the phase of the reflected wave can cover the full 2π range by rotating the unit cells in a manner similar to that of the Pancharatnam-Berry (PB) phase metasurface. Rigorous theoretical analyses are provided. Numerical validation demonstrates that the cross-polarization reflectance of the metasurface exceeds 0.7 within the frequency range of 0.7044 to 2.0859 THz, corresponding to nearly 100% relative bandwidth. The modulation accuracy of the polarization angle can reach within 1 degree. The proposed metasurface may find applications in communication, imaging, sensing, and other fields.

High-Throughput Growth of Armored Perovskite Single Crystal Fibers for Pixelated Arrays

The poor machinability of halide perovskite crystals severely hampered their practical applications. Here a high-throughput growth method is reported for armored perovskite single-crystal fibers (SCFs). The mold-embedded melt growth (MEG) method provides each SCF with a capillary quartz shell, thus guaranteeing their integrality when cutting and polishing. Hundreds of perovskite SCFs, exemplified by CsPbBr3, CsPbCl3, and CsPbBr2.5I0.5, with customized dimensions (inner diameters of 150-1000 µm and length of several centimeters), are grown in one batch, with all the SCFs bearing homogeneity in shape, orientation, and optical/electronic properties. Versatile assembly protocols are proposed to directly integrate the SCFs into arrays. The assembled array detectors demonstrated low-level dark currents (< 1 nA) with negligible drift, low detection limit (< 44.84 nGy s-1), and high sensitivity (61147 µC Gy-1 cm-2). Moreover, the SCFs as isolated pixels are free of signal crosstalk while showing uniform X-ray photocurrents, which is in favor of high spatial resolution X-ray imaging. As both MEG and the assembly of SCFs involve none sophisticated processes limiting the scalable fabrication, the strategy is considered to meet the preconditions of high-throughput productions.

A Rapid Fabrication Method of Large-Area MLAs with Variable Curvature for Retroreflectors Based on Thermal Reflow

Retroreflectors are an important optical component, but current retroreflector structures and manufacturing processes are relatively complex. This paper proposes a rapid, low-cost, large-area method for fabricating retroreflectors based on microlens arrays. Tunable microlens arrays with adjustable curvature, fill factor, and sizes were prepared using photolithography and thermal reflow techniques. Subsequently, a two-step nanoimprinting process was used to create a flexible reverse mold and transfer the structure onto the desired substrate. The microlens arrays, with a diameter of 30 μm, a period of 33 μm, a curvature radius ranging from 15.5 to 18.8 μm, and a fill factor ranging from 75.1% to 88.8%, were fabricated this way. In addition, the method also fabricated microlens arrays with diameters ranging from 10 to 80 μm. Retroreflectors were made by sputtering a layer of silver on the MLAs as a reflecting layer, and tests showed that the microlens-based retroreflector exhibited superior retroreflective performance with a wide-angle response of ±75°. Microlens-based retroreflectors have the advantages of simple operation and controllable profiles. The fabrication method in this paper is suitable for large-scale production, providing a new approach to retroreflector design.

Ultrahigh precision laser nanoprinting based on defect-compensated digital holography for fast-fabricating optical metalenses

The 3D structured light field manipulated by a digital-micromirror-device (DMD)-based digital hologram has demonstrated its superiority in fast-fabricating stereo nanostructures. However, this technique intrinsically suffers from defects of light intensity in generating modulated focal spots, which prevents from achieving high-precision micro/nanodevices. In this Letter, we have demonstrated a compensation approach based on adapting spatial voxel density for fabricating optical metalenses with ultrahigh precision. The modulated focal spot experiences intensity fluctuations of up to 3% by changing the spatial position, leading to a 20% variation of the structural dimension in fabrication. By altering the voxel density to improve the uniformity of the laser cumulative exposure dosage over the fabrication region, we achieved an increased dimensional uniformity from 94.4% to 97.6% in fabricated pillars. This approach enables fast fabrication of metalenses capable of sub-diffraction focusing of 0.44λ/NA with the increased mainlobe-sidelobe ratio from 1:0.34 to 1:0.14. A 6 × 5 supercritical lens array is fabricated within 2 min, paving a way for the fast fabrication of large-scale photonic devices.

Review of Droplet Printing Technologies for Flexible Electronic Devices: Materials, Control, and Applications

Flexible devices have extensive applications in areas including wearable sensors, healthcare, smart packaging, energy, automotive and aerospace sectors, and other related fields. Droplet printing technology can be utilized to print flexible electronic components with micro/nanostructures on various scales, exhibiting good compatibility and wide material applicability for device production. This paper provides a comprehensive review of the current research status of droplet printing technologies and their applications across various domains, aiming to offer a valuable reference for researchers in related areas.

Circular-target-style bifocal zoom metalens

Optical zoom plays an important role in realizing high-quality image magnification, especially in photography, telescopes, microscopes, etc. Compared to traditional bulky zoom lenses, the high versatility and flexibility of metalens design provide opportunities for modern electronic and photonic systems with demands for miniature and lightweight optical zoom. Here, we propose an ultra-thin, lightweight and compact bifocal zoom metalens, which consists of a conventional circular sub-aperture and a sparse annular sub-aperture with different focal lengths. The imaging resolutions of such single zoom metalens with 164 lp/mm and 117 lp/mm at magnifications of 1× and 2× have been numerically and experimentally demonstrated, respectively. Furthermore, clear zoom images of a dragonfly wing pattern have been also achieved using this zoom metalens, showing its distinctive aspect in biological imaging. Our results provide an approach for potential applications in integrated optical systems, miniaturized imaging devices, and wearable devices.