Recent progress on metasurfaces: applications and fabrication
About: This article is published in Journal of Physics D.The article was published on 2021-09-23. It has received 29 citations till now. The article focuses on the topics: Nanoimprint lithography.
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TL;DR: In this article , second-order photonic topological insulators (SPTIs) with topologically protected corner states were proposed in C 4v -symmetric lattices.
Abstract: Abstract Second-order photonic topological insulators (SPTIs) with topologically protected corner states provide a unique platform for realizing the robust manipulation of light in lower dimensions. Previous SPTIs proposed in C 4v -symmetric lattices are mainly based on the two-dimensional (2D) Su-Schrieffer–Heeger (SSH) model consisting of an even number of sites in the unit cell. Moreover, second-order topological phases within high-order band gaps are rarely explored. Here, we propose a new principle of SPTIs beyond the 2D SSH model, which is realized in C 4v-symmetric lattices consisting of an odd number of sites in the unit cell. The midgap-gap-ratios of these odd-order band gaps, from the first-order to the nineteenth-order with step of two-order, are maximized by the method of topology optimization. Second-order topological phases are successfully created within these sizeable band gaps and highly localized corner states are observed. Our work offers a new route for exploring high-order topological states in photonics and other classical systems.
15 citations
TL;DR: In this paper , the fundamental principles and practical design procedures to exploit the abilities of metalenses, including achromaticity, high numerical aperture, and tunability, are presented, along with a practical guide for the design, fabrication, and critical considerations of metalense with examples of early works to more recent developments.
Abstract: Metalenses comprised of artificial subwavelength structures known as meta-atoms have demonstrated abilities beyond conventional bulky optical components by modulating the phase, amplitude, and polarization of light in an ultrathin planar form factor. In this Tutorial, we present the fundamental principles and practical design procedures to exploit the abilities of metalenses, including achromaticity, high numerical aperture, and tunability. The fundamental principles include both plasmonic and dielectric meta-atoms, which require different physics to describe their light–matter interactions. In the phase modulation section, we compare the methods of physically implementing phase via meta-atoms including both the propagation and geometric phase methods. Next, we cover the recent progress of nanofabrication procedures from the perspective of the metalenses using materials such as titanium dioxide, gallium nitride, and hydrogenated amorphous silicon. We further compare the various fabrication methods with regard to the resolution, size, cost, and optical properties of fabricated metalenses. Then, we describe the critical considerations of metalenses including aberration-correction, numerical aperture, and tunability for advanced flat optics. Herein, we provide a practical guide for the design, fabrication, and critical considerations of metalenses with examples of research from early works to more recent developments.
14 citations
TL;DR: In this paper , a theory is developed that analytically links the properties of the scatterer from which a metasurface is made, to its response via the lattice coupling matrix.
Abstract: Optical metasurfaces consist of 2D arrangements of scatterers, and they control the amplitude, phase, and polarization of an incidence field on demand. Optical metasurfaces are the cornerstone for a future generation of flat optical devices in a wide range of applications. The rapid advances in nanofabrication have made the versatile design and analysis of these ultra-thin surfaces an ever-growing necessity. However, a comprehensive theory to describe the optical response of periodic metasurfaces in closed-form and analytical expressions has not been formulated, and prior attempts are frequently approximate. Here, a theory is developed that analytically links the properties of the scatterer, from which a metasurface is made, to its response via the lattice coupling matrix. The scatterers are represented by their polarizability or T matrix. Explicit expressions for the optical response up to octupolar order in both spherical and Cartesian coordinates are provided, for normal or oblique incidence. Several examples demonstrate that the proposed theoretical approach is a powerful tool for exploring the physics of metasurfaces and designing novel flat optics devices. Novel fully-diffracting metagratings and particle-independent polarization filters are proposed, and novel insights into bound states in the continuum, collective lattice resonances, and the response of Huygens’ metasurfaces under oblique incidence are provided.
13 citations
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TL;DR: In this paper, a theory that analytically links the properties of the scatterer from which a periodic metasurface is made, to its optical response via the lattice coupling matrix is presented.
Abstract: Optical metasurfaces consist of a 2D arrangement of scatterers, and they control the amplitude, phase, and polarization of an incidence field on demand. Optical metasurfaces are the cornerstone for a future generation of flat optical devices in a wide range of applications. The rapidly growing advances in nanofabrication have made the versatile design and analysis of these ultra-thin surfaces an ever-growing necessity. However, despite their importance, a comprehensive theory to describe the optical response of periodic metasurfaces in closed-form and analytical expressions has not been formulated, and prior attempts were frequently approximate. Here, we develop a theory that analytically links the properties of the scatterer, from which a periodic metasurface is made, to its optical response via the lattice coupling matrix. The scatterers are represented by their polarizability or T matrix, and our theory works for normal and oblique incidence. We provide explicit expressions for the optical response up to octupolar order in both spherical and Cartesian coordinates. Several examples demonstrate that our analytical tool constitutes a paradigm shift in designing and understanding optical metasurfaces. Novel fully-diffracting metagratings and particle-independent polarization filters are proposed, and novel insights into the response of Huygens' metasurfaces under oblique incidence are provided. Our analytical expressions are a powerful tool for exploring the physics of metasurfaces and designing novel flat optics devices.
13 citations
TL;DR: In this article , a gap-shifted split ring resonator (SRR) was used to achieve spin angular momentum selection and achieved the maximum calculated circular dichroism in reflection (CDR) of 0.91.
Abstract: Abstract Tunable metasurfaces can replace conventional bulky active optical modules to realize practical flat optical devices such as lenses, LiDAR, holography, and augmented reality. However, tunable metasurfaces have generally been limited to switching between two distinct states. Here, we present liquid crystal (LC) integrated chiral metasurfaces, of which the metahologram intensity can be adjusted continuously between fully ‘on’ and ‘off’ states. The chiral metasurface consists of a gap-shifted split ring resonator (SRR), and exhibits spin angular momentum selection that reflects left-circularly-polarized light but perfectly absorbs right-circularly-polarized light (99.9%). The gap-shifted SRR realizes spin angular momentum selection using a metal–dielectric–metal multilayer structure and thereby induces a strong gap-plasmonic response, achieving the maximum calculated circular dichroism in reflection (CDR) of 0.99 at the wavelength of 635 nm. With the chiral metasurface, metaholograms are demonstrated with tunable intensities using LCs that change the polarization state of the output light using an applied voltage. With the LC integrated chiral metasurfaces, 23 steps of polarization are demonstrated for the continuous tuning of the holographic image intensity, achieving measured CDR of 0.91. The proposed LC integrated spin-selective chiral metasurface provides a new resource for development of compact active optical modules with continuously-tunable intensity.
8 citations
References
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TL;DR: In this article, a two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint phase discontinuities on propagating light as it traverses the interface between two media.
Abstract: Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.
6,763 citations
TL;DR: The results firmly establish that metalenses can have widespread applications in laser-based microscopy, imaging, and spectroscopy, with image qualities comparable to a state-of-the-art commercial objective.
Abstract: Subwavelength resolution imaging requires high numerical aperture (NA) lenses, which are bulky and expensive. Metasurfaces allow the miniaturization of conventional refractive optics into planar structures. We show that high-aspect-ratio titanium dioxide metasurfaces can be fabricated and designed as metalenses with NA = 0.8. Diffraction-limited focusing is demonstrated at wavelengths of 405, 532, and 660 nm with corresponding efficiencies of 86, 73, and 66%. The metalenses can resolve nanoscale features separated by subwavelength distances and provide magnification as high as 170×, with image qualities comparable to a state-of-the-art commercial objective. Our results firmly establish that metalenses can have widespread applications in laser-based microscopy, imaging, and spectroscopy.
2,406 citations
TL;DR: In this paper, a high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated, which uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness.
Abstract: A high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated. The technique uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness. Metal patterns with a feature size of 25 nanometers and a period of 70 nanometers were fabricated with the use of resist templates created by imprint lithography in combination with a lift-off process. With further development, imprint lithography should allow fabrication of sub-10-nanometer structures and may become a commercially viable technique for manufacturing integrated circuits and other nanodevices.
2,396 citations
TL;DR: The design of the hologram integrates a ground metal plane with a geometric metasurface that enhances the conversion efficiency between the two circular polarization states, leading to high diffraction efficiency without complicating the fabrication process.
Abstract: Using a metasurface comprising an array of nanorods with different orientations and a backreflector, a hologram image can be obtained in the visible and near-infrared with limited loss of light intensity.
2,075 citations
TL;DR: The experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum are described.
Abstract: Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies.
1,978 citations