Basis function approach for diffractive pattern generation with Dammann vortex metasurfaces

A Multichannel Metasurface for Multiprotocol Quantum Key Distributions

Multiprotocol quantum key distribution (mQKD) enables users to flexibly select protocols for secure quantum communication, though achieving mQKD introduces considerable system complexity and resource demands. Here, we report the first realization of mQKD using a metasurface, which generates multiple hybrid states of photonic spin angular momentum (SAM) and orbital angular momentum (OAM) and distributes them to different users. The incident polarization-entangled photon pair interacts with the metasurface, producing four SAM-OAM hybrid states with high fidelity through spin-orbit conversion. Among these hybrid states, two execute the BB84 protocol, while the other two perform the BBM92 protocol, all demonstrating high secret key rates and low quantum bit error rates. This approach provides a robust, compact solution for generating and distributing SAM-OAM hybrid states and stands out for the remarkable capability of a metasurface in secured information processing.

Monolithic silicon carbide metasurfaces for engineering arbitrary 3D perfect vector vortex beams

Perfect vector vortex beams (PVVBs) can precisely control the light's polarization and phase along tailored intensity profiles, offering significant potential for advanced applications such as optical trapping and optical encryption. Extending PVVBs from 2D to 3D configurations would provide an additional spatial control dimension and enhance their information capacity. However, a compact and low-loss solution to generating 3D PVVBs remains unresolved. Here, we propose and demonstrate the use of monolithic silicon carbide metasurfaces with polarization-dependent phase-only modulation to engineer arbitrary PVVBs in 3D space. We reconstruct the 3D intensity and polarization distributions of PVVBs along customized trajectories, showing their independence from polarization orders and spherical coordinates on the Poincaré sphere. Additionally, we demonstrate a monolithic metasurface that encodes parallel-channel 3D PVVBs for information encryption. The 3D PVVBs generated from minimalist metasurfaces hold great promise for multidimensional micromanipulation and laser micromachining, high-security information processing and high-dimensional quantum entanglement.

Non-Interleaved Shared-Aperture Full-Stokes Metalens via Prior-Knowledge-Driven Inverse Design

Characterization of electromagnetic wave polarization states is critical in various applications of materials, biomedical, and imaging. The emergence of metasurfaces opens up the possibility of implementing highly integrated full-Stokes imagers. Despite rapid development, prevailing schemes on metasurface-based full-Stokes imagers require interleaved or cascaded designs, inevitably resulting in performance deterioration, bulky size, and complicating the imaging procedure due to misalignment. To overcome these challenges, a non-interleaved shared-aperture full-Stokes metalens enabled by the prior-knowledge-driven inverse design methodology is proposed. The metalens can be directly deployed into imagers, performing high-accuracy diffraction-limited full-Stokes imaging without other ancillary components, breaking intrinsic constraints of efficiency and resolution in interleaved design. To demonstrate this, the metalens is integrated into the W-band passive imaging system, as an alternative solution, to perform polarimetric imaging, which reduces the reliance on the high cost and high complexity of the ortho-mode transducer and broadband correlator in traditional polarimetric radiometers. Furthermore, with the assistance of a 3D reconstruction method, the feasibility of multi-polarization information for contactless surface slope measurements is explored. This work may open new paradigms for the full-Stokes imager designing and broaden the applications of metasurface polarimetric imaging.

Optical computing metasurfaces: applications and advances

Integrated photonic devices and artificial intelligence have presented a significant opportunity for the advancement of optical computing in practical applications. Optical computing technology is a unique computing system based on optical devices and computing functions, which significantly differs from the traditional electronic computing technology. On the other hand, optical computing technology offers the advantages such as fast speed, low energy consumption, and high parallelism. Yet there are still challenges such as device integration and portability. In the burgeoning development of micro-nano optics technology, especially the deeply ingrained concept of metasurface technique, it provides an advanced platform for optical computing applications, including edge detection, image or motion recognition, logic computation, and on-chip optical computing. With the aim of providing a comprehensive introduction and perspective for optical computing metasurface applications, we review the recent research advances of optical computing, from nanostructure and computing methods to practical applications. In this work, we review the challenges and analysis of optical computing metasurfaces in engineering field and look forward to the future development trends of optical computing.

Single-shot deterministic complex amplitude imaging with a single-layer metalens

Conventional imaging systems can only capture light intensity. Meanwhile, the lost phase information may be critical for a variety of applications such as label-free microscopy and optical metrology. Existing phase retrieval techniques typically require a bulky setup, multiframe measurements, or prior information of the target scene. Here, we proposed an extremely compact system for complex amplitude imaging, leveraging the extreme versatility of a single-layer metalens to generate spatially multiplexed and polarization phase-shifted point spread functions. Combining the metalens with a polarization camera, the system can simultaneously record four polarization shearing interference patterns along both in-plane directions, thus allowing the deterministic reconstruction of the complex amplitude light field in a single shot. Using an incoherent light-emitting diode as the illumination, we experimentally demonstrated speckle-noise-free complex amplitude imaging for both static and moving objects with tailored magnification ratio and field of view. The miniaturized and robust system may open the door for complex amplitude imaging in portable devices for point-of-care applications.

Efficient fabrication of infrared antireflective microstructures on a curved Diamond-ZnS composite surface by using femtosecond Bessel-like beams

Antireflective microstructures fabricated using femtosecond laser possess wide-ranging applicability and high stability across different spectral bands. However, due to the limited aspect ratio of the focused light field, traditional femtosecond laser manufacturing faces challenges in efficiently fabricating antireflective microstructures with high aspect ratio and small period, which are essential for antireflection, on curved surfaces. In this study, we present a robust and efficient method for fabricating high-aspect-ratio and basal surface insensitive antireflective microstructures using a spatially shaped Bessel-like beam. Based on theoretical simulation, a redesigned telescopic system is proposed to flexibly equalize the intensity of the Bessel beam along its propagation direction, facilitating the fabrication of antireflective subwavelength structures on the entire convex lens. The fabricated microstructures, featuring a width of less than 2 µm and a depth of 1 µm, enhance transmittance from 75% to 85% on Diamond-ZnS composite material (D-ZnS) surfaces. Our approach enables the creation of high aspect ratio subwavelength structures with a z-position difference exceeding 600 µm. This practical, efficient, and cost-effective method is facilitated for producing antireflective surfaces on aero-optical components utilized in aviation.

Realizing depth measurement and edge detection based on a single metasurface

How to simultaneously obtain the depth, edge, and other light information of the scene to accurately perceive the physical world is an important issue for imaging systems. However, such tasks usually require bulky optical components and active illumination methods. Here, we design and experimentally validate a single geometric metasurface that can achieve depth measurement or edge detection under incoherent or coherent light respectively. Double helix point source function is utilized, and three verification experiments are carried out, including double-helix beam calibration, 2D object and 3D object detection, respectively. Additionally, two-dimensional edge detection can also be achieved. This compact imaging system can enable new applications in various fields, from machine vision to microscopy.

Advances in Meta-Optics and Metasurfaces: Fundamentals and Applications

Meta-optics based on metasurfaces that interact strongly with light has been an active area of research in recent years. The development of meta-optics has always been driven by human's pursuits of the ultimate miniaturization of optical elements, on-demand design and control of light beams, and processing hidden modalities of light. Underpinned by meta-optical physics, meta-optical devices have produced potentially disruptive applications in light manipulation and ultra-light optics. Among them, optical metalens are most fundamental and prominent meta-devices, owing to their powerful abilities in advanced imaging and image processing, and their novel functionalities in light manipulation. This review focuses on recent advances in the fundamentals and applications of the field defined by excavating new optical physics and breaking the limitations of light manipulation. In addition, we have deeply explored the metalenses and metalens-based devices with novel functionalities, and their applications in computational imaging and image processing. We also provide an outlook on this active field in the end.