Large-area Metasurface Research Articles

Adjoint-Optimized Large Dielectric Metasurface for Enhanced Purcell Factor and Directional Photon Emission.

Extracting photons efficiently from quantum sources, such as atoms, molecules, and quantum dots, is crucial for various nanophotonic systems used in quantum communication, sensing, and computation. To improve the performance of these systems, it is not only necessary to provide an environment that maximizes the number of optical modes, but it is also desirable to guide the extracted light toward specific directions. One way to achieve this goal is to use a large area metasurface that can steer the beam. Previous work has used small aperture devices that are fundamentally limited in their ability to achieve high directivity. This work proposes an adjoint-based topology optimization approach to design a large light extractor that can enhance the spontaneous decay rate of the embedded quantum transition and collimate the extracted photons. With the help of this approach, we present all-dielectric metasurfaces for a quantum transition emitting at λ = 600 nm. These metasurfaces achieve a broadband improvement of spontaneous emission compared to that in the vacuum, reaching a 10× enhancement at the design frequency. Furthermore, they can beam the extracted light into a narrow cone (±10°) along a desired direction that is predefined through their respective design process.

Large-area, omnidirectional metasurface exhibiting unpolarized broadband absorption

Despite the ongoing efforts to design and fabricate large-area metasurface absorbers using cost-effective fabrication processes and low-cost materials, significant challenges persist. In this study, we present an anodized aluminum oxide template-assisted metasurface absorber with an area of 4 cm2, which incorporates glue cylinder arrays, a low-cost nickel layer, and protective glue layers. This device achieved an average absorptivity of approximately 91% (90% in the experiment) in the 200–900 nm wavelength range. The absorption level remained above 80% even at incident angles up to 45°, with calculated and experimental values of 92% and 82%, respectively. Moreover, the absorption is not sensitive to the thickness of the residual glue layers, making it ideal for roll-to-roll nanoimprinting processes. Therefore, the proposed metasurface absorber offers an alternative method for achieving broadband absorption in an effective manner and has great potential for related applications.

Sub-wavelength patterned pulse laser lithography for efficient fabrication of large-area metasurfaces

Rigorously designed sub-micrometer structure arrays are widely used in metasurfaces for light modulation. One of the glaring restrictions is the unavailability of easily accessible fabrication methods to efficiently produce large-area and freely designed structure arrays with nanoscale resolution. We develop a patterned pulse laser lithography (PPLL) approach to create structure arrays with sub-wavelength feature resolution and periods from less than 1 μm to over 15 μm on large-area thin films with substrates under ambient conditions. Separated ultrafast laser pulses with patterned wavefront by quasi-binary phase masks rapidly create periodic ablated/modified structures by high-speed scanning. The gradient intensity boundary and circular polarization of the wavefront weaken diffraction and polarization-dependent asymmetricity effects during light propagation for high uniformity. Structural units of metasurfaces are obtained on metal and inorganic photoresist films, such as antennas, catenaries, and nanogratings. We demonstrate a large-area metasurface (10 × 10 mm2) revealing excellent infrared absorption (3–7 μm), which comprises 250,000 concentric rings and takes only 5 minutes to produce.

End-to-end metasurface inverse design for single-shot multi-channel imaging.

We introduce end-to-end inverse design for multi-channel imaging, in which a nanophotonic frontend is optimized in conjunction with an image-processing backend to extract depth, spectral and polarization channels from a single monochrome image. Unlike diffractive optics, we show that subwavelength-scale "metasurface" designs can easily distinguish similar wavelength and polarization inputs. The proposed technique integrates a single-layer metasurface frontend with an efficient Tikhonov reconstruction backend, without any additional optics except a grayscale sensor. Our method yields multi-channel imaging by spontaneous demultiplexing: the metaoptics front-end separates different channels into distinct spatial domains whose locations on the sensor are optimally discovered by the inverse-design algorithm. We present large-area metasurface designs, compatible with standard lithography, for multi-spectral imaging, depth-spectral imaging, and "all-in-one" spectro-polarimetric-depth imaging with robust reconstruction performance (≲ 10% error with 1% detector noise). In contrast to neural networks, our framework is physically interpretable and does not require large training sets. It can be used to reconstruct arbitrary three-dimensional scenes with full multi-wavelength spectra and polarization textures.

Chemical Vapor Deposition of Spherical Amorphous Selenium Mie Resonators for Infrared Meta-Optics.

Applying direct growth and deposition of optical surfaces holds great promise for the advancement of future nanophotonic technologies. Here, we report on a chemical vapor deposition (CVD) technique for depositing amorphous selenium (a-Se) spheres by desorption of selenium from Bi2Se3 and re-adsorption on the substrate. We utilize this process to grow scalable, large area Se spheres on several substrates and characterize their Mie-resonant response in the mid-infrared (MIR) spectral range. We demonstrate size-tunable Mie resonances spanning the 2-16 μm spectral range for single isolated resonators and large area ensembles. We further demonstrate strong absorption dips of up to 90% in ensembles of particles in a broad MIR range. Finally, we show that ultra-high-Q resonances arise in the case where Se Mie-resonators are coupled to low-loss epsilon-near-zero (ENZ) substrates. These findings demonstrate the enabling potential of amorphous Selenium as a versatile and tunable nanophotonic material that may open up avenues for on-chip MIR spectroscopy, chemical sensing, spectral imaging, and large area metasurface fabrication.

Imaging-based spectrometer-less optofluidic biosensors based on dielectric metasurfaces for detecting extracellular vesicles

Biosensors are indispensable tools for public, global, and personalized healthcare as they provide tests that can be used from early disease detection and treatment monitoring to preventing pandemics. We introduce single-wavelength imaging biosensors capable of reconstructing spectral shift information induced by biomarkers dynamically using an advanced data processing technique based on an optimal linear estimator. Our method achieves superior sensitivity without wavelength scanning or spectroscopy instruments. We engineered diatomic dielectric metasurfaces supporting bound states in the continuum that allows high-quality resonances with accessible near-fields by in-plane symmetry breaking. The large-area metasurface chips are configured as microarrays and integrated with microfluidics on an imaging platform for real-time detection of breast cancer extracellular vesicles encompassing exosomes. The optofluidic system has high sensing performance with nearly 70 1/RIU figure-of-merit enabling detection of on average 0.41 nanoparticle/µm2 and real-time measurements of extracellular vesicles binding from down to 204 femtomolar solutions. Our biosensors provide the robustness of spectrometric approaches while substituting complex instrumentation with a single-wavelength light source and a complementary-metal-oxide-semiconductor camera, paving the way toward miniaturized devices for point-of-care diagnostics.

Large-area all-dielectric metasurface fabricated by an anodized aluminum oxide template

Transmissive metasurfaces formed by high-index dielectric materials have received great attention due to its potential in holograms, deflectors, beam converters, and flat lenses. However, a key challenge of all-dielectric metasurfaces is the limited scale and high cost in fabrication, such as electron beam lithography (EBL) and focused ion beam (FIB) lithography. In this paper, for the first time to our knowledge, an anodized aluminum oxide (AAO) template is combined with titanium dioxide (TiO2) metasurface fabrication with advantages of large area (>2cm2) and low cost. Using the ordered anodized aluminum oxide (AAO) as an evaporation mask, a TiO2 nanocylinder array is deposited through the AAO mask onto the SiO2 substrate. Electric and magnetic dipole resonances of TiO2 metasurface appear in the visible spectrum. Furthermore, we demonstrate the interaction of the CsPbBr1.5I1.5 quantum dot (QD) emission with magnetic dipole (MD) resonance of TiO2 metasurface. Our results reveal that the metasurface exhibits remarkable photoluminescence (PL) enhancement of 25%. Up to now, a TiO2 metasurface with 2.25-cm2-large area using AAO template method has never been attempted. Different from the metasurfaces fabricated by FIB and EBL, our method offers great ease for large-area metasurface fabrication, which is convenient for metasurface researchers and avoids costly facilities.

Low-loss, centimeter-scale plasmonic metasurface for ultrafast optoelectronics

Plasmonics can dramatically improve the radiative properties of fluorescent materials by precisely tailoring the local density of states, but has largely been dismissed for practical optoelectronic applications due to losses and lack of scalability to macroscopic areas. Here, we demonstrate a low-loss plasmonic metasurface that can collect fast-modulated light with a 3 dB bandwidth exceeding 14 GHz and a 120º acceptance angle and convert it to a directional source with, to the best of our knowledge, a record-high overall efficiency of ∼ 30 % . This large-area metasurface composed of fluorescent dye coupled to nanopatch antennas, exhibits a 910-fold increase in the overall fluorescence and a 133-fold emission rate enhancement—values previously only observable for isolated, highly optimized single nanostructures. Critical for future applications ranging from optoelectronics to biosensing, this metasurface was created over macroscopic areas with scalable techniques and the performance was validated over centimeter-scale regions. In particular, we believe this approach shows promise for the burgeoning field of visible/near-infrared wireless communications, where radical new designs and materials are needed for ultrafast, efficient, omnidirectional detectors and incoherent sources.

Large-area, low-cost near-infrared meta-surface reflector based on a pixelated two-dimensional silicon disk array.

All-dielectric meta-surfaces composed of dielectric meta-atoms with electric and magnetic multipole resonances provide a low loss alternative to plasmonic meta-surfaces in some optical research fields such as meta-lens and meta-surface holography. We utilize the digital holography lithography technique to obtain the large area meta-surface perfect reflector made of high refractive index and low loss silicon discs arrays, with the capability to delicately control the optical response in the near infrared spectrum. Three types of meta-surface reflectors (discs, truncated cones and diamond-shaped discs) were fabricated, which correspondingly exhibited nearly 1 peak reflectance and greater than 97% average reflectance in their respective perfect reflectance spectral regions. Digital holography lithography only takes 4 min to fabricate millions of photoresist disks over an area of 100 mm2, which is high processing efficiency and low cost. The fabrication strategy opens a new avenue for the production of large-area meta-surfaces in the optical field, especially in the mass production of optical communication devices, semiconductor lasers, etc.

Pixeled metasurface for multiwavelength detection of vitamin D

AbstractThe steadily increasing demand for accurate analysis of vitamin D level,viameasurement of its best general marker, 25-hydroxyvitamin D (25(OH)D), pushes for the development of novel automated assays capable of working at very low concentrations. Here, we propose a plasmonic biosensor of 25(OH)D3 (calcifediol) based on surface-enhanced infrared absorption spectroscopy, which exploits the resonant coupling between plasmonic nanoantennas and vibrational excitation of small molecules. Specifically, our proposed platform features a large-area (several mm2) metasurface made of gold nanoantennas fabricated on a silicon substrate, comprising different macroregions (“pixels”) of area 500 × 500 µm2. In each pixel, the nanoantenna geometrical parameters are tuned so as to support localized surface plasmon resonances (and hence large field enhancements at the nanoscale) within different regions of the infrared spectrum. As a result, a single chip is capable of performing analysis from the region of functional groups to that of fingerprint. Two different designs are fabricatedviaelectron beam lithography, functionalized with a correlated antibody for the detection of 25(OH)D3, and characterizedviaFourier-transform infrared spectroscopy. Our experiments demonstrate the capability to detect a concentration as low as 86 pmol/L, and an amount of immobilized small molecules of 25(OH)D3 monohydrate (molecular weight: 418.65 g/mol) as low as 4.31 amol over an area of 100 × 100 µm2.

Large-area metasurface on CMOS-compatible fabrication platform: driving flat optics from lab to fab

Abstract A metasurface is a layer of subwavelength-scale nanostructures that can be used to design functional devices in ultrathin form. Various metasurface-based optical devices – coined as flat optics devices – have been realized with distinction performances in research laboratories using electron beam lithography. To make such devices mass producible at low cost, metasurfaces over a large area have also been defined with lithography steppers and scanners, which are commonly used in semiconductor foundries. This work reviews the metasurface process platforms and functional devices fabricated using complementary metal-oxide-semiconductor-compatible mass manufacturing technologies. Taking both fine critical dimension and mass production into account, the platforms developed at the Institute of Microelectronics (IME), A*STAR using advanced 12-inch immersion lithography have been presented with details, including process flow and demonstrated optical functionalities. These developed platforms aim to drive the flat optics from lab to fab.

Adhesive-Layer-Free and Double-Faced Nanotransfer Lithography for a Flexible Large-Area MetaSurface Hologram.

Herein, we develop an adhesive-free double-faced nanotransfer lithography (ADNT) technique based on the surface deformation of flexible substrates under the conditions of temperature and pressure control and thus address the challenge of realizing the mass production of large-area nanodevices in the fields of optics, metasurfaces, and holograms. During ADNT, which is conducted on a flexible polymer substrate above its glass transition temperature in the absence of adhesive materials and chemical bonding agents, nanostructures from the polymer stamp are attached to the deformed polymer substrate. Various silicon masters are employed to prove our method applicable to arbitrary nanopatterns, and diverse Ag and Au nanostructures are deposited on polymer molds to demonstrate the wide scope of useable metals. Finally, ADNT is used to (i) produce a flexible large-area hologram on the defect-free poly(methyl methacrylate) (PMMA) film and (ii) fabricate a metasurface hologram and a color filter on the front and back surfaces of the PMMA film, respectively, to realize dual functionality. Thus, it is concluded that the use of ADNT can decrease the fabrication time and cost of high-density nanodevices and facilitate their commercialization.

Overlapping domains for topology optimization of large-area metasurfaces.

We introduce an overlapping-domain approach to large-area metasurface design, in which each simulated domain consists of a unit cell and overlapping regions from the neighboring cells plus PML absorbers. We show that our approach generates greatly improved metalens quality compared to designs produced using a locally periodic approximation, thanks to ∼10× better accuracy with similar computational cost. We use the new approach with topology optimization to design large-area (200λ) high-NA (0.71) multichrome and broadband achromatic lenses with high focusing efficiency (∼50%), greatly improving upon previously reported works.

Plasmon hybridization engineering in self-organized anisotropic metasurfaces

The engineering of self-organized plasmonic metasurfaces is demonstrated using a maskless technique with defocused ion-beam sputtering and kinetically controlled deposition. The proposed reliable, cost-effective, and controllable approach enables large-area (order of square centimeter) sub-wavelength periodic patterning with close-packed gold nanostrips. A multi-level variant of the method leads to high-resolution manufacturing of vertically stacked nanostrip dimer arrays, without resorting to lithographic approaches. The design of these self-organized metasurfaces is optimized by employing plasmon hybridization methods. In particular, preliminary results on the so-called gap-plasmon configuration of the nanostrip dimers, implementing magnetic dipole resonance in the near-infrared range, are reported. This resonance offers a superior sensitivity and field enhancement, compared with the more conventional electric dipole resonance. The translational invariance of the nanostrip configuration leads to a high filling factor of the hot spots. These advanced features make the large-area metasurface based on gap-plasmon nanostrip dimers very attractive for surface-enhanced linear and nonlinear spectroscopy (e.g., surface-enhanced Raman scattering) and plasmon-enhanced photon harvesting in solar and photovoltaic cells.

Perfect infrared absorber and emitter based on a large-area metasurface

Metasurfaces with metal-insulator-metal structures have attracted significant attention because of their high optical performance. Their spectral emissivity/absorptivity can be modulated with geometrically controlled electromagnetic resonances. However, practical fabrication of these materials in the meter scale remains a challenge. In the present study, an aluminum- and ceria-based metasurface that exhibits nearly perfect emission/absorption in the infrared region was designed. Furthermore, we succeeded in fabricating the proposed metasurface in the meter scale via photolithography and wet etching. This study enhances understanding of underlying resonance mechanisms with electromagnetic simulations and equivalent circuit model, and will facilitate the experimental design of high-efficiency large-area metasurfaces.

Large-area, broadband and high-efficiency near-infrared linear polarization manipulating metasurface fabricated by orthogonal interference lithography

Manipulation of the polarization state using electromagnetic metasurface has attracted considerable attention in recent years. However, most previously demonstrated single-layer polarization conversion metasurfaces suffer from low polarization conversion efficiency, narrow operation bandwidth, or huge fabrication challenges, especially for the visible and near-infrared frequencies. In this letter, a broadband and high-efficiency reflective linear polarization converter composed of ellipse-shaped plasmonic planar resonator was demonstrated in the near-infrared region. A polarization conversion ratio in power larger than 91.1% is achieved from 730 nm to 1870 nm. Furthermore, orthogonal interference lithography is adopted to prepare the large-area optical polarization conversion metasurface. The fabrication strategy unplugs the bottleneck of the fabrication of the large-area metasurface in the optical regime, promising an unprecedented progress for optical communication and integrated optics.