Integration Of Metasurfaces Research Articles

Utilizing Metasurfaces for Directional Control of LED Emission

This study provides a detailed modeling and analysis of four different three-dimensional GaN-based LED structures. The results reveal that incorporating DBRs effectively focuses light and enhances the light extraction efficiency (LEE). Additionally, the integration of Metasurface in the Micro-LED+DBRs+M structure allows for precise control of light emission direction and further radiation focusing. Furthermore, in the Micro-LED+DBRs+M2 structure with improved periodic nanocolumns, the light beam can be deflected simultaneously in multiple directions. These findings offer new possibilities for the advancement of LED technology.

Microfluidic Metasurfaces: A New Frontier in Electromagnetic Wave Engineering

AbstractMetasurfaces, as 2D artificial electromagnetic materials, play a pivotal role in manipulating electromagnetic waves by controlling their amplitude, phase, and polarization. Achieving this control involves designing subwavelength meta‐molecules with specific geometries and periodicities. In the context of microfluidic metasurfaces, optical properties can be dynamically modulated by altering either the geometric structure of liquid meta‐molecules or the refractive index of the liquid medium. Leveraging the fluidity of liquid materials, microfluidic metasurfaces exhibit remarkable performance in terms of reconfigurability and flexibility. These properties not only establish a cutting‐edge research area but also broaden the scope of applications for active metasurface devices. Additionally, the integration of metasurfaces within microfluidic systems has led to novel functionalities, including enhanced particle manipulation and sensor technologies. Compared to conventional solid‐material‐based metasurfaces, microfluidic metasurfaces offer greater design freedom, making them advantageous for diverse fields such as electromagnetic absorption, optical sensing, holographic displays, and tunable optical meta‐devices like flat lenses and polarizers. This review provides insights into the characteristics, modulation techniques, and potential applications of microfluidic metasurfaces, illuminating both the current research landscape and promising avenues for further explorations.

Hybrid meta/refractive lens design with an inverse design using physical optics

Hybrid lenses are created by combining metasurface optics with refractive optics, where refractive elements contribute optical power, while metasurfaces correct optical aberrations. We present an algorithm for optimizing metasurface nanostructures within a hybrid lens, allowing flexible interleaving of metasurface and refractive optics in the optical train. To efficiently optimize metasurface nanostructures, we develop a scalar field, ray-wave hybrid propagation method. This method facilitates the propagation of incident and derived adjoint fields through optical elements, enabling effective metasurface optimization within the framework of adjoint gradient optimization. Numerical examples of various lens configurations are presented to illustrate the versatility of the algorithm and showcase the benefits offered by the proposed approach, allowing metasurfaces to be positioned beyond the image space of a lens. Taking a F/2, 40° field-of-view, midwave infrared lens as an example, the lens exhibits an average focusing efficiency of 38% before the integration of metasurfaces. Utilizing the new algorithm to design two metasurfaces—one in the object space and one in the image space—results in significant enhancement of the average focusing efficiency to over 90%. In contrast, a counterpart design with both metasurfaces limited to the image space yields a lower average focusing efficiency of 73%.

Inverse-designed metasurfaces with facile fabrication parameters

Optical metasurfaces are planar nanostructured devices that are industrially attractive in part because they utilize high-throughput microelectronic fabrication techniques for implementation. It is therefore critical to develop design paradigms that can balance the realization of highly efficient wavefront responses together with device manufacturability. We introduce a gradient-based design framework for freeform metasurfaces in which nanoscale elements are explicitly constrained to feature basic shapes, nearly uniform feature sizes, and exceptionally low aspect ratios. In spite of the apparent uniformity of the metasurface geometric features, the devices are able to utilize nonlocal near-field optical coupling to achieve highly efficient and extreme wavefront scattering beyond conventional design methodologies. Utilizing this approach, we design facile high-numerical-aperture devices such as beam deflectors and large-area metalenses capable of diffraction-limited focusing. We anticipate that these concepts can facilitate the design and integration of metasurfaces into monolithic optical systems.

Gigahertz-rate-switchable wavefront shaping through integration of metasurfaces with photonic integrated circuit

Gigahertz-rate-switchable wavefront shaping through integration of metasurfaces with photonic integrated circuit

Advancing wavefront shaping with resonant nonlocal metasurfaces: beyond the limitations of lookup tables

Resonant metasurfaces are of paramount importance in addressing the growing demand for reduced thickness and complexity, while ensuring high optical efficiency. This becomes particularly crucial in overcoming fabrication challenges associated with high aspect ratio structures, thereby enabling seamless integration of metasurfaces with electronic components at an advanced level. However, traditional design approaches relying on lookup tables and local field approximations often fail to achieve optimal performance, especially for nonlocal resonant metasurfaces. In this study, we investigate the use of statistical learning optimization techniques for nonlocal resonant metasurfaces, with a specific emphasis on the role of near-field coupling in wavefront shaping beyond single unit cell simulations. Our study achieves significant advancements in the design theoretical conception of resonant metasurfaces. For transmission-based metasurfaces, a beam steering design outperforms the classical design by achieving an impressive efficiency of 80% compared to the previous 23%. Additionally, our optimized extended depth-of-focus (EDOF) metalens yields a remarkable five-fold increase in focal depth, a four-fold enhancement in focusing power compared to conventional designs and an optical resolution superior to 600 cycle/mm across the focus region. Moreover, our study demonstrates remarkable performance with a wavelength-selected beam steering metagrating in reflection, achieving exceptional efficiency surpassing 85%. This far outperforms classical gradient phase distribution approaches, emphasizing the immense potential for groundbreaking applications in the field of resonant metasurfaces.

Broadband low radar cross section antennas based on H‐shaped metasurface

AbstractThis paper presents a novel metasurface antenna element and a novel metasurface antenna array, both of which have broadband low radar cross section (RCS) performance. The antenna element is constructed by two kinds of H‐shaped metasurface unit cells. One kind of H‐shaped metasurface unit cells is properly fed to radiate, and the other unit cells are used to cancel the scattering field from the former. Thus, an integration of metasurface and antenna is performed and broadband low RCS is obtained. Furthermore, a H‐shaped metasurface antenna array is also proposed by deliberately introducing metallic vias for isolation. Both the proposed antenna element and the array have almost the same radiation performance with conventional patch antennas. Numerical calculations and experimental measurements are conducted. The results verify the effectiveness of the proposed novel antennas.

Low-RCS electromagnetic metasurface antenna based on shared-aperture technique

In this paper, a novel shared-aperture method of electromagnetic metasurface and antenna is proposed to obtain low radar-cross-section (RCS) performance. In this method, the low-RCS metasurface is first designed, then this metasurface is combined with traditional antenna to obtain novel low-RCS antenna based on shared-aperture technique. Besides, the analysis and corresponding local structure modification are also conducted to ensure that the antenna has good radiation performance while reducing broadband RCS. Using this method, a dual-layer polarization rotation unit cell is first proposed and its broadband working principle is investigated by both theoretical analysis and numerical comparison. Based on this unit cell, a broadband low-RCS metasurface is constructed. Then an initial shared-aperture metasurface antenna is obtained by substituting the middle cells in the metasurface with traditional patch antenna directly. Through careful analysis of surface current in radiation mode, the gain decrease of this metasurface antenna is revealed. On this basis, a finite removal strategy is put forward and some metasurface cells in the antenna are removed by using the electric current analysis. Consequently, an improved shared-aperture metasurface antenna is proposed. This improved antenna works in a frequency range from 6.3 to 7.48 GHz, which is slightly wider than the traditional patch antenna. Its gain is also higher than that of traditional antenna, with a maximum improvement of 1 dB. Meanwhile, the apparent RCS decreases from 6 to 16 GHz for any polarized incident wave, and the reduction peak is larger than 20 dB. Finally, fabrications and measurements are conducted. The measurement results and numerical calculations are in good agreement. The well-behaved radiation performance and broadband low-RCS property of this metasurface antenna verify the effectiveness of the proposed method. Unlike most of reported design methods of low-RCS antennas directly from traditional antennas, the proposed method adopts reverse thinking to transform scattering optimization into radiation optimization, realizing the integration between metasurface and antenna, thus making low-RCS antenna design easier and faster.

Dynamic Spectral Modulation on Meta-Waveguides Utilizing Liquid Crystal.

The integration of metasurfaces and optical waveguides is gradually attracting the attention of researchers because it allows for more efficient manipulation and guidance of light. However, most of the existing studies focus on passive devices, which lack dynamic modulation. This work utilizes the meta-waveguides with liquid crystal(LC) to modulate the on-chip spectrum, which is the first experimentally verified, to the authors' knowledge. By applying a voltage, the refractive index of the liquid crystal surrounding the meta-waveguides can be tuned, resulting in a blue shift of the spectrum. The simulation shows that the 18.4dB switching ratio can be achieved at 1550nm. The meta-waveguides are prepared using electron beam lithography (EBL), and the improved transmittance of the spectrum in the short wavelength is experimentally verified, which is consistent with the simulation trend. At 1551.64nm wavelength, the device achieves a switching ratio of ≈16dB with an active area of 8µm × 0.4µm. Based on this device, an optoelectronic computing architecture for the Hadamard matrix product and a novel wavelength selection switch are proposed. This work offers a promising avenue for on-chip dynamic modulation in integrated photonics, which has the advantage of a compact active area, fast response time, and low energy consumption compared to conventional thermal-light modulation.

Nanoantenna induced liquid crystal alignment for high performance tunable metasurface.

Liquid crystal (LC) based spatial light modulators (SLMs) are a type of versatile device capable of arbitrarily reconfiguring the wavefront of light. For current commercial LC-SLM devices, the large pixel size limits their application to diffractive optics and 3D holographic displays. Pixel miniaturization of these devices is challenging due to emerging inter-pixel crosstalk, ultimately linked to the thick LC layer necessary for full phase (or amplitude) control. Integration of metasurfaces, i.e., 2D arrangements of resonant nanoantennas, with thin LC has emerged as a promising platform to boost light modulation, enabling realization of sub-wavelength pixel size SLMs with full phase (or amplitude) control. In most devices realized so far, however, the presence of an alignment layer, necessary to induce a preferential initial LC orientation, increases the voltage requirement for resonance tuning and reduces the efficiency of light modulation, something that accentuates for an ultra-thin (e.g., submicron) metasurface-LC cell. Here, we present an alternative strategy by which the LC molecular alignment is purely controlled by the periodicity and geometry of the nanoantenna without any additional alignment layer. The nanoantennas are specifically designed for the double purpose of sustaining optical resonances that are used for light modulation and to, simultaneously, induce the required LC pre-alignment. The proposed device structure allows lower voltage and reduced switching times (sub-millisecond) compared to devices including the alignment layer. This novel strategy thus helps to improve the performance of these miniaturized-pixel devices, which have emerged as one of the potential candidates for the next generation of products in a wide range of applications, from virtual/augmented reality (VR/AR) and solid-state light detection and ranging (LiDAR), to 3D holographic displays and beyond.

Dual-Functional Tunable Metasurface for Meta-Axicon with a Variable Depth of Focus and Continuous-Zoom Metalens.

Optical metasurfaces have been widely investigated for their versatile ability to manipulate wavefront and miniaturize traditional optical components into ultrathin planar devices. The integration of metasurfaces with multifunctionality and tunability has fundamentally transformed optics with unprecedented control over light propagation and manipulation. This study introduces a pioneering framework for the development of tunable metasurfaces with multifunctionality, and an example of a tunable metasurface of dual functionalities is proposed and numerically verified as one of the tunable meta-axicon for generating Bessel beams with a variable depth of focus (DOF) and a continuous-zoom metalens. Specifically, this design achieves dual-functional phase modulation by helicity-multiplexing from the combination of the geometric phase as well as the propagation phase and realizes tunability for both functionalities through rotational actuation between double metasurface layers. As a result, dual functionalities with continuous tunability of the proposed TiO2 metasurface are enabled independently for the left and right circularly polarized (LCP and RCP) incidences at 532 nm. Specifically, LCP light triggers the metasurface to function as a tunable axicon, generating non-diffracting Bessel beams with variable numerical apertures (NA) and DOFs. Conversely, the RCP incidence induces it to operate as a continuous-zoom metalens and generates variable spherical wavefront focusing on diverse focal lengths. This study not only initially implements the design of tunable meta-axicon, but also achieves the integration of such a tunable meta-axicon and continuous-zoom metalens within a single metasurface configuration. The proposed device could find potential applications in biological imaging, microscopic measurement, laser fabrication, optical manipulation, multi-plane imaging, depth estimation, optical data storage, etc.

A Review of Optical Tweezers with Metasurfaces

Optical tweezers (OTs) have made significant progress in recent years, realizing the non-contact optical manipulation of target objects through the interaction between light and matter. In addition to trapping particles with the intensity gradient of the beam, a series of complex optical elements are required to properly modulate the beams to expand the operation of optical manipulation. The development of metasurfaces alleviates this problem. Due to the merits of miniaturization, planarization, multi-function, and integration of metasurfaces, these kinds of novel devices have been applied in OT systems. Metasurface devices have been used to replace traditional objective lenses, achieving device integration and even obtaining multi-function of OTs with unique optical properties in applications. OTs with metasurfaces have developed rapidly, and a great deal of work has been carried out on OTs with metasurfaces, as well as discussions on their practical applications. In this review, we regard the latest progress in the field of OTs with metasurfaces. We classify OTs with metasurface and summarize the new impetus brought by metasurfaces for the development of OTs.

Metasurfaces integrated with a single-mode waveguide array for off-chip wavefront shaping.

Integration of metasurfaces and SOI (silicon-on-insulator) chips can leverage the advantages of both metamaterials and silicon photonics, enabling novel light shaping functionalities in planar, compact devices that are compatible with CMOS (complementary metal-oxide-semiconductor) production. To facilitate light extraction from a two-dimensional metasurface vertically into free space, the established approach is to use a wide waveguide. However, the multi-modal feature of such wide waveguides can render the device vulnerable to mode distortion. Here, we propose a different approach, where an array of narrow, single-mode waveguides is used instead of a wide, multi-mode waveguide. This approach tolerates nano-scatterers with a relatively high scattering efficiency, for example Si nanopillars that are in direct contact with the waveguides. Two example devices are designed and numerically studied as demonstrations: the first being a beam deflector that deflects light into the same direction regardless of the direction of input light, and the second being a light-focusing metalens. This work shows a straightforward approach of metasurface-SOI chip integration, which could be useful for emerging applications such as metalens arrays and neural probes that require off-chip light shaping from relatively small metasurfaces.

Interparticle-Coupled Metasurface for Infrared Plasmonic Absorption

Plasmonic metasurfaces operating in the long-wavelength infrared region (LWIR) are primarily employed for bio-sensing and imaging applications. The key factor affecting the capability of LWIR metasurfaces is absorption efficiency, whereas significant advances have been made to attain higher absorption intensities, using metal-insulator-metal (MIM) stack structures, which require a complex nanofabrication process and repetition of the patterning process to develop each layer. This study experimentally demonstrates the integration of metasurfaces with plasmonic resonators. The metasurfaces and plasmonic resonators are developed through electron beam lithography (EBL) on the same plane of the Silicon substrate. The fabricated prototype has broad incident angle stability at a bandwidth of 2μm with near-perfect absorption at 8μm resonance wavelength when characterized through the Attenuated Total Reflectance - Fourier Transforms Infrared Spectroscopy (ATR-FTIR) setup. The metasurface device achieves tunable resonance behavior when the incident angles reach up to 70°. The proposed integration of metasurface with plasmonic resonators are well-suited for enhanced biosensing applications with metasurface devices.

Static Beam Steering by Applying Metasurfaces on Photonic-Crystal Surface-Emitting Lasers

Photonic-crystal surface-emitting laser (PCSEL) holds promise for laser beam with high efficacy while retain the small divergence angle, being now all the rage as laser source in modern opto-electronic technologies to replace edge emitting lasers and vertical-cavity surface-emitting lasers (VCSELs). Arbitrary beam shaping and deflection of VCSELs with ultra-thin flat optics, aka metasurfaces, has recently demonstrated, making possibility to realize a compact system in many technologies. However, the large divergence angle and limited output power at single fundamental mode of the VCSEL limits its application. Here, we report the static steering of laser beam with high efficiency and near 1° divergence angle by shining the laser beam of the PCSEL through the metasurface array placed on top. The small divergence angle is contributed from PCSEL. On the other hand, the metasurface array offers the higher efficiency beam deflection, without considering additional collimating or focusing. This provides highly flexible platform and is capable to manipulate the laser emission through the design of the metasurfaces and the PCSELs. Moreover, the beam proprieties can be further modified for specific application through the metasurfaces. The integration of metasurface with PCSEL provides the compact and collimated laser source, promising more accurate generation of versatile laser sources on demand for automotive ultra-compact light detection and ranging (LiDAR), depth sensing, optical communication, etc.

All‐In‐One Integrated Multifunctional Broadband Metasurface for Analogue Signal Processing, Polarization Conversion, Beam Manipulation, and Near‐Field Sensing

AbstractProgrammable metasurface, or reconfigurable intelligent surface is one of the most promising strategies to enhance communication and sensing capacities via arrays of reconfigurable meta‐atoms. The functionalities of conventional programmable metasurfaces are usually limited, and active meta‐atoms are connected with steering‐logic board through cables, which makes the whole system inconvenient for installation and stable use. Here an all‐in‐one integrated multifunctional metasurface for various application purpose is proposed. The integration of metasurface and steering‐logic board produces an all‐in‐one system, which makes it compact, low profile, and stable. The novel meta‐atom structure provides all‐in‐one functionalities, including 1) dispersion‐reconfigurable spatial phaser for analogue signal processing, 2) polarization conversion, 3) beam steering and orbital angular momentum generation for high‐speed communication and, 4) near‐field scanning for sensing. The proposed metasurface also has a broadband property, which is operating from 9.5 to 10.5 GHz with 10% relative bandwidth. Such a design integrates functionalities of signal processing, communication, and sensing in a single programmable metasurface, which makes it especially useful for integrated sensing and communication toward next‐generation wireless networks.

Optical Fiber-Integrated Metasurfaces: An Emerging Platform for Multiple Optical Applications.

The advent of metasurface technology has revolutionized the field of optics and photonics in recent years due to its capability of engineering optical wavefronts with well-patterned nanostructures at subwavelength scale. Meanwhile, inspired and benefited from the tremendous success of the “lab-on-fiber” concept, the integration of metasurface with optical fibers has drawn particular interest in the last decade, which establishes a novel technological platform towards the development of “all-in-fiber” metasurface-based devices. Thereby, this review aims to present and summarize the optical fiber-integrated metasurfaces with the current state of the art. The application scenarios of the optical fiber metasurface-based devices are well classified and discussed accordingly, with a brief explanation of physical fundamentals and design methods. The key fabrication methods corresponding to various optical fiber metasurfaces are summarized and compared. Furthermore, the challenges and potential future research directions of optical fiber metasurfaces are addressed to further leverage the flexibility and versatility of meta-fiber-based devices. It is believed that the optical fiber metasurfaces, as a novel all-around technological platform, will be exploited for a large range of applications in telecommunication, sensing, imaging, and biomedicine.

MEMS-tunable dielectric metasurface lens using thin-film PZT for large displacements at low voltages.

Tunable focusing is a desired property in a wide range of optical imaging and sensing technologies but has tended to require bulky components that cannot be integrated on-chip and have slow actuation speeds. Recently, integration of metasurfaces into electrostatic micro-electromechanical system (MEMS) architectures has shown potential to overcome these challenges but has offered limited out-of-plane displacement range while requiring large voltages. We demonstrate for the first time, to the best of our knowledge, a movable metasurface lens actuated by integrated thin-film PZT MEMS, which has the advantage of offering large displacements at low voltages. An out-of-plane displacement of a metasurface in the range of 7.2 μm is demonstrated under a voltage application of 23 V. This is roughly twice the displacement at a quarter of the voltage of state of the art electrostatic out-of-plane actuation of metasurfaces. Using this tunability, we demonstrate a varifocal lens doublet with a focal shift of the order of 250 μm at the wavelength 1.55μm. The thin-film PZT MEMS-metasurface is a promising platform for miniaturized varifocal components.

Metasurfaces 2.0: Laser-integrated and with vector field control

The past decade has witnessed the rapid development of metasurfaces. In this paper, we outline our thinking on what we regard as two important trends in metasurface research, namely, the continual improvement in the light field modulation capacity of metasurfaces and the integration of metasurfaces with other devices to achieve fully contained optical systems. We first describe one of the fastest growing branches of the former, which is known as metasurface-based vectorial holography. This aims to control the wavefront and the polarization state of a light beam simultaneously. In comparison with single function devices, i.e., those that modulate the wavefront or polarization but not both, metasurface vectorial holography represents a significant improvement in our ability to modulate light fields. We then discuss the integration of metasurfaces with lasers for the goal of direct modulation of the polarization of the output beam or for the generation of beams with tailored orbital angular momenta. Two methods for doing so are discussed, namely, on-facet integration and in-cavity integration. We hope this Perspective will provide readers with new insights and thus help extend applications of metasurface-based optical devices.

Electro-optic lithium niobate metasurfaces

Many applications of metasurfaces require an ability to dynamically change their properties in the time domain. Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of metasurfaces with optoelectronic devices. In this work, we propose and experimentally demonstrate an electro-optic lithium niobate (EO-LN) metasurface that shows dynamic modulations to phase retardation of transmitted light. Quasi-bound states in the continuum (QBIC) are observed from this metasurface. By applying external electric voltages, the refractive index of lithium niobate (LN) is changed by Pockels EO nonlinearity, leading to efficient phase modulations to the transmitted light around the QBIC wavelength. The EO-LN metasurface developed in this study opens up new routes for potential applications in the field of displaying, pulse shaping, and spatial light modulating.