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Experimental characterization of achromatic metalenses. a Schematic depicting the optical setup. The optics for mapping the 3D far-field of the metalenses are mounted on a motorized stage. A flip mirror allows light to pass from a target focal plane to a power meter for efficiency measurements. b Optical image of a sample metalens. Scale bar: 25 μm. c Measured far-field intensity distributions of metalens M1A, composed of Generation 1A meta-units and with diameter D = 100 μm and target focal length f = 200 μm, corresponding to NA = 0.24. Measured normalized intensity distributions in the axial plane (x-z cross section) are shown for select wavelengths spanning from 1300 to 1660 nm. The x-y cross sections are shown at the target focal plane for each wavelength. d Corresponding experimental results for metalens M1B, composed of Generation 1B metaunits, showing substantially suppressed parasitic focal spots, little elongation of the depth of focus as observed in c, and larger operational bandwidth
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Small, high-performance imaging systems could be built using flat lenses made from specially arranged nanoscale pillars. Traditional lenses rely on the curvature and thickness of glass to focus light, but metalenses, which can be smaller, thinner, and more flexible, have surfaces comprised of thousands of nanoscale pillars whose geometries are care...
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... metalenses are summarized in Supplementary Information Table S1). We fabricated these metalenses using a standard electron beam litho- graphy, lift-off, and etch procedure (Materials and meth- ods section). Scanning electron microscope images of two sample fabricated metalenses are shown in Fig. 2g, h. Using the custom-built setup shown in Fig. 3a, we char- acterized the three-dimensional (3D) intensity distribu- tion of light exiting the fabricated ...
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... the Generation 1A library, we realized an achromatic metalens, M1A, with a diameter of 100 µm, designed focal length of 200 µm (NA ≈ 0.24), and opera- tional bandwidth of λ = 1300-1650 nm. The measured intensity distributions in the focal (x-y cross section) and axial (x-z cross section) planes at different wavelengths for M1A are plotted in Fig. 3c. From the axial intensity distributions, we can see that the chromatic aberration is significantly reduced across the entire operating band- width, with the focal planes for all wavelengths lying very close to one another. It is important to stress that this is a continuous aberration correction over the entire designed wavelength ...
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... therefore designed and fabricated metalens M1B, with the same size and NA as M1A, using the taller meta- units from the Generation 1B library. The corresponding measured focal and axial intensity distributions are plot- ted in Fig. 3d and show substantially suppressed parasitic focal spots and little elongation of the DOF. The wave- length range over which the chromatic aberration is corrected is also expanded to λ = 1200-1650 nm, a 100- nm improvement over the operational bandwidth of M1A. The combination of size, NA, and bandwidth of M1B reaches the fundamental ...
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... aberration correction over a reduced operational bandwidth of λ = 1200-1400 nm (Fig. 4c). Figure 5 summarizes important figures of merit, including the focal length, focusing efficiency, focal spot size, and Strehl ratio, for all of the fabricated metalenses. Figure 5a shows focal plane intensity profiles at the selected wavelengths shown in Fig. 3d for metalens M1B; Fig. 5b shows corresponding horizontal and vertical cuts of the measured focal spots with an ideal Airy disk overlaid for comparison. The results show nearly diffraction-limited focal spots for all wavelengths with no obvious distortion. Figure 5c shows the measured focal lengths of the metalenses at sampled ...
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... the experimental setup (Fig. 3a), a collimated laser beam with a tunable wavelength is incident on the metalens, and the 3D far-field of the lens is measured by acquiring a stack of 2D images at different distances from the lens. The tunable laser beam is generated by passing the emission from a supercontinuum laser source (NKT SuperK Extreme) through a mono- ...
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... These include anapole mode [5][6][7], Fano resonance [8][9][10], and electromagnetically-induced transparency [11][12][13]. The unique capabilities of metasurfaces have led to planar optical meta-components with a wide range of applications across both microwave and optical frequencies in the fields of imaging and lensing [14][15][16][17], holography [18][19][20], structural color printing [21][22][23], energy harvesting [24][25][26], and perfect absorbers [27][28][29], among others. Importantly, the recent development of all-dielectric metasurfaces especially benefit from highly efficient transmission applications [30][31][32]. ...
In this study, we investigate a novel "dimerized" dielectric metasurface featuring dual-mode resonances governed by symmetry-protected bound states in the continuum (BICs). The metasurface design offers advantages such as insensitivity to incident light polarization and exceptionally high quality factors exceeding 10$^5$ for low and moderate structural deviations from the monoatomic array. By introducing mastered perturbations in the metasurface via the Brillouin zone folding method, without reducing symmetry, we explore the behavior of symmetry-protected BIC states and their polarization-independent responses. Through numerical simulations and analysis, we demonstrate the superiority of Q factors for specific BIC-based resonances, leading to precise control over interaction behaviors and light engineering in both near and far fields. Our findings contribute to the understanding of BIC resonance interactions and offer insights into the design of high-performance sensing applications and meta-devices with enhanced functionalities.
... Similarly, an incident plane wave that passes through a lens will converge at the diagonally opposite point on the surface of the lens. Numerous techniques exist for beam focusing, including the utilization of surface plasmon polaritons in quasi-planar structures [10][11][12] and broadband achromatic lenses based on gradient metasurfaces [13][14][15]. ...
Multi-beam microwave antennas have attracted enormous attention owing to their wide range of applications in communication systems. Here, we propose a broadband metamaterial-based multi-beam Luneburg lens-antenna with low polarization sensitivity. The lens is constructed from additively manufactured spherical layers, where the effective permittivity of the constituting elements is obtained by adjusting the ratio of dielectric material to air. Flexible microstrip patch antennas operating at different frequencies are used as primary feeds illuminating the lens to validate the radiation features of the lens-antenna system. The proposed Luneburg lens-antenna achieves ±72° beam scanning angle over a broad frequency range spanning from 2 GHz to 8 GHz and presents a gain between 15.3 dBi and 22 dBi, suggesting potential applications in microwave-and millimeter-wave mobile communications, radar detection and remote sensing.
... Arrays of individual scatterers, termed "meta-units", provide the local phase, amplitude, and polarization modulation required to shape the reflected or transmitted wavefront. [1][2][3][4][5][6][7] State-of-the-art metasurfaces are thin, compact devices that can offer a compelling alternative to conventional bulk optics and radio-frequency antennas with a wide range of potential applications, including communications, [8][9][10] imaging, [11][12][13][14] sensing, [15] and holography. [16][17][18] Work on metasurfaces has predominantly focused on flat, rigid devices due to reliance on planar fabrication techniques such as lithography and laser cutting. ...
Lightweight, low‐cost metasurfaces and reflectarrays that are easy to stow and deploy are desirable for many terrestrial and space‐based communications and sensing applications. This work demonstrates a lightweight, flexible metasurface platform based on flat‐knit textiles operating in the cm‐wave spectral range. By using a colorwork knitting approach called float‐jacquard knitting to directly integrate an array of resonant metallic antennas into a textile, we realize two textile reflectarray devices, a metasurface lens (metalens) and a vortex‐beam generator. Operating as a receiving antenna, the metalens focuses a collimated normal‐incidence beam to a diffraction‐limited, off‐broadside focal spot. Operating as a transmitting antenna, the metalens converts the divergent emission from a horn antenna into a collimated beam with peak measured directivity, gain, and efficiency of 21.30 dB, 15.30 dB, and –6.00 dB (25.12%), respectively. The vortex‐beam generating metasurface produces a focused vortex beam with a topological charge of m = 1 over a wide frequency range of 4.1‐5.8 GHz. Strong specular reflection is observed for our textile reflectarrays, caused by wavy yarn floats on the backside of the float‐jacquard textiles. Our work demonstrates a novel approach for scalable production of flexible metasurfaces by leveraging commercially available yarns and well‐established knitting machinery and techniques.
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... Manipulating the dimensions, configurations, and periodicity of metasurface structures empowers precise control over electromagnetic wavefronts. Metasurfaces boost diverse applications, including super-lenses [25][26][27], full-color holographic metasurfaces [28], polarization conversion devices [29], programmable metasurfaces [30], metasurface antennas [31] and more. Due to the planar structure, metasurfaces have negligible thickness and are compatible with semiconductor manufacturing processes, making them an ideal candidate for greatly reducing the volume of the optical path structure. ...
Recent research has focused on miniaturizing atomic devices like magnetometers and gyroscopes for quantum precision measurements, leading to energy savings and broader application. This paper presents the design and validation of metasurface-based optical elements for atomic magnetometers’ optical paths. These include highly efficient half-wave plates, polarizers, circular polarization generators, polarization-preserving reflectors, and polarizing beam splitters. These components, compatible with semiconductor manufacturing, offer a promising solution for creating ultra-thin, compact atomic devices.
... However, this strategy suffers from discrete frequency and low efficiency. More recently, broadband achromatic lenses have been fabricated by optimizing the spectral degrees of freedom in the lens phase profiles [24] or introducing light frequency-domain coherence optimization [25]. Despite this impressive progress, a new approach toward the programable chromatic dispersion of planar lenses with large size, high efficiency and compact design is still urgently pursued. ...
Wavefront control is the fundamental requirement in optical informatics. Planar optics have drawn intensive attention due to the merits of compactness and light weight. However, it remains a challenge to freely manipulate the dispersion, hindering practical applications, especially in imaging. Here, we propose the concept of frequency-synthesized phase engineering to solve this problem. A phasefront-frequency matrix is properly designed to encode different spatial phases to separate frequencies, thus makes arbitrary dispersion tailoring and even frequency-separated functionalization possible. The periodically rotated director endows cholesteric liquid crystal with a spin and frequency selective reflection. Moreover, via presetting the local initial orientation of liquid crystal, geometric phase is encoded to the reflected light. We verify the proposed strategy by cascading the chiral anisotropic optical media of specifically designed helical pitches and initial director orientations. By this means, planar lenses with RGB achromatic, enhanced chromatic aberration and color routing properties are demonstrated. Inch-sized and high-efficient lenses are fabricated with low crosstalk among colors. It releases the freedom of dispersion control of planar optics, and even enables frequency decoupled phase modulations. This work brings new insights to functional planar optics and may upgrade the performance of existing optical apparatuses.
... By appropriately designing a pattern of meta-atoms, one can manipulate the intensity, phase, polarization state, and wavelength dispersion of light incident on the surface with a high degree of freedom. Optical metasurfaces with designed wavelength dispersions are referred to as dispersion-engineered metasurfaces; they are the basis for single-layer achromatic metasurface lenses (metalenses), which have recently attracted significant attention in the field of optics [23][24][25][26][27]. We have extended the concept of dispersion-engineered metasurfaces and have developed a metasurface-based color splitter that splits incident white (W) light into R, G, and B light on high-density pixels [28,29]. ...
... Note that the spatial modulation used in wavefront shaping can be of the amplitude or the phase of the light, but phase-only modulation is the most used because of its high transmission efficiency. Dispersion-engineered metasurfaces extend this basic idea across the wavelength dimension and independently control the wavefront for each wavelength [23][24][25][26][27]. To perform spatial phase-modulation independently for each wavelength with meta-atoms, each meta-atom must be designed to have the desired phases at all designed wavelengths at the same time. ...
... It is also evident that the phase dispersion is wider than that of a waveguide made from only square nanoposts (the conventional choice for the dielectric meta-atoms of optical metasurfaces). In addition, these meta-atoms work in a polarization-independent manner due to their four-fold rotational symmetry [25,26]. Therefore, such meta-atoms can be used to make polarization-independent wavefront shaping designs for each wavelength. ...
Increasing the sensitivity of image sensors is a major challenge for current imaging technology. Researchers are tackling it because highly sensitive sensors enable objects to be recognized even in dark environments, which is critical for today’s smartphones, wearable devices, and automobiles. Unfortunately, conventional image-sensor architectures use light-absorptive color filters on every pixel, which fundamentally limits the detected light power per pixel. Recent advances in optical metasurfaces have led to the creation of pixelated light-transmissive color splitters with the potential to enhance sensor sensitivity. These metasurfaces can be used instead of color filters to distinguish primary colors, and unlike color filters, they can direct almost all of the incident light to the photodetectors, thereby maximizing the detectable light power. This review focuses on such metasurface-based color splitters enabling high-sensitivity color-image sensors. Their underlying principles are introduced with a focus on dispersion engineering. Then, their capabilities as optical elements are assessed on the basis of our recent findings. Finally, it is discussed how they can be used to create high-sensitivity color-image sensors.
... However, the phase discontinuity of metalens can also lead to image distortion and blur. The design of achromatic metalens is still limited by large aperture and low Fnumber [11,12]. ...
Lenses have been a cornerstone of optical systems for centuries; however, they are inherently limited by the laws of physics, particularly in terms of size and weight. Because of their characteristic light weight, small size, and subwavelength modulation, metalenses have the potential to miniaturize and integrate imaging systems. However, metalenses still face the problem that chromatic aberration affects the clarity and accuracy of images. A high-quality image system based on the end-to-end joint optimization of a neural network and an achromatic metalens is demonstrated in this paper. In the multi-scale encoder–decoder network, both the phase characteristics of the metalens and the hyperparameters of the neural network are optimized to obtain high-resolution images. The average peak-signal-to-noise ratio (PSNR) and average structure similarity (SSIM) of the recovered images reach 28.53 and 0.83. This method enables full-color and high-performance imaging in the visible band. Our approach holds promise for a wide range of applications, including medical imaging, remote sensing, and consumer electronics.
... On the contrary, metasurfaces have the ability to control electromagnetic wave properties (such as phase, amplitude, and polarization) in a subwavelength resolution by arranging the artificially designed sub-wavelength structured nanopillars array in a proper way [1][2][3][4]. Research on metasurfaces has made significant progress recently, and various planar optical devices have been realized, such as beam-bending generators [5,6], holograms [7][8][9][10][11][12], color filters [13,14], polarization converter [15][16][17], vortex beam generators [18][19][20][21] and metalenses [22][23][24][25][26], etc. Owing to their high integration and processing technology, and their compatibility for the manufacture of complementary metal-oxidesemiconductor (CMOS), metasurface devices have unprecedented advantages over traditional optical devices with the same functions [27][28][29][30]. Therefore, the metasurface is expected to revolutionize in various fields of optics and photonics. ...
... µm) through the Si nanopillars by applying unit cell boundary conditions in xand y-directions under plane wave incidence, thereby obtaining the corresponding normalized transmission phase and amplitude response. We use a hexagonal lattice instead of a square because it has the densest planar packing arrangement, which leads to a smoother sampling of the phase near the boundary of each zone and results in better performance compared to a square lattice [22,24]. The Si nanopillars were placed at the centers of each hexagonal unit cell, as shown in Fig. 1 (The different colors in Fig. 1(a) are just to better visually distinguish between nanopillars and substrates). ...
... μm) through the Si nanopillars by applying unit cell boundary conditions in xand y-directions under plane wave incidence, thereby obtaining the corresponding normalized transmission phase and amplitude response. We use a hexagonal lattice instead of a square because it has the densest planar packing arrangement, which leads to a smoother sampling of the phase near the boundary of each zone and results in better performance compared to a square lattice [22,24]. The Si nanopillars were placed at the centers of each hexagonal unit cell, as shown in Fig. 1 (The different colors in Fig. 1a are just to better visually distinguish between nanopillars and substrates). ...
In this article, we explored the design and simulation techniques of large-aperture metalenses, and the optimization design methods of metalenses. For verification and experimental demonstration, a centimeter-scale aperture single-layer metalens and a field of view optimized metalens doublet,composed of subwavelength-spaced Si nanopillars with an operating wavelength of 3.77 µm were designed and manufactured. Finally, the focusing performance of the two under narrow-band laser irradiation was characterized, and an imaging demonstration of the metalens doublet was performed under an optical bandwidth of 250 nm (3500-3750 nm). We envision that the calculation, design, sample manufacturing and demonstration research on large-aperture metalens presented here will provide an important reference for the design and verification of large-aperture metasurface lenses or special metasurface devices in the future, such as large-aperture compact multifunctional metalens optical equipment for low-load special application systems like airborne, spaceborne, missile, satellite and deep sea.
... Scanning-electron micrograph and optical micrograph of one of the lenses are shown in Fig. 1b-c respectively. The metalens design based on truncated waveguides 12 is deliberately exploited to facilitate comparison to existing results in the literature [17][18][19][20][21][22][23][24][25][26][27][28] . The lenses were manufactured using EBL and reactive ion etching (RIE). ...
... In general, the lower efficiency in the 1st order, the more energy in other orders, and this is why we see the bright spot effect. The 2nd order focal point is closer to the lens than the 1st order, and [17][18][19][20][21][22][23][24][25][26][27] . The measurements from this paper are included (black stars, error bars in Fig. 2). ...
... Simulation -CPA, RFA Our use of the constant phase approximation (CPA)where each metaatom is replaced by a constant amplitude and phase, found from the 0 th order mode amplitude, and then propagated to the far-fieldis probably the most widespread method for designing metalenses 2,11,22 . Resolved field approximation (RFA) instead resolves the scalar E field (same polarisation) right on top of the meta-pillar in a low-resolution Cartesian point grid. ...
Metalenses are flat lenses, where sub-wavelength, so-called meta-atoms manipulate the electric field to perform a given lens function. Compared to traditional lenses, the two main drawbacks of metalenses are their achromatic limitations and low efficiencies. While an abundance of simulations show that efficiencies above 90% are attainable for low numerical apertures (NA), experimental reports showing such high efficiencies are limited. Here, we use electron-beam lithography (EBL) to realize a set of lenses with varying NA from 0.08 to 0.93. The low NAs were expected to fit the model, and the higher NAs determine the validity range of the model. We find that measured efficiencies above 92% for NA = 0.24 are achievable, and that a slight modification of the simulation model extends its validility to NA = 0.6. Based on our results, we discuss that the lower efficiencies reported in the literature are caused by low-fidelity manufacturing, closing the efficiency gap between measurements and simulation in metalens fabrication.
... A novel solution extensively explored in recent years is the so-called metasurfaces, which are two-dimensional periodic structures consisting of subwavelength dielectric or metallic units (i.e., meta-atoms) [1][2][3][4]. Metasurfaces can enable an almost arbitrary manipulation of a wavefront with various phases, including resonance phase [5][6][7], propagation phase [8][9][10], and Pancharatnam-Berry (PB) phase [11][12][13][14][15]. The PB phase is particularly attractive since it can cover 2π full range within a broadband of frequencies. ...
Pancharatnam–Berry (PB) metasurfaces can be applied to manipulate the phase and polarization of light within subwavelength thickness. The underlying mechanism is attributed to the geometric phase originating from the longitudinal spin of light. Here, we demonstrate, to the best of our knowledge, a new type of PB geometric phase derived from the intrinsic transverse spin of guided light. Using full-wave numerical simulations, we show that the rotation of a metallic nano-bar sitting on a metal substrate can induce a geometric phase covering 2 π full range for the surface plasmons carrying an intrinsic transverse spin. Especially, the geometric phase is different for the surface plasmons propagating in opposite directions due to spin-momentum locking. We apply the geometric phase to design metasurfaces to manipulate the wavefront of surface plasmons to achieve steering and focusing. Our work provides a new mechanism for on-chip light manipulations with potential applications in designing ultra-compact optical devices for imaging and sensing.
