Abstract:Metalenses
are nanostructured surfaces that mimic the functionality
of optical elements. Many exciting demonstrations have already been
made, for example, focusing into diffraction-limited spots or achromatic
operation over a wide wavelength range. The key functionality that
is yet missing, however, and that is most important for applications
such as smartphones or virtual reality, is the ability to perform
the imaging function with a single element over a wide field of view.
Here, by relaxing the constraint o… Show more
“…1 , the optical symmetry transformation is performed through a single radial-quadratic phase mask ( ), which is mathematically expressed as 48 : where k 0 is the wavevector in free space, θ is the oblique angle of the incident light, and f is the focal length of the phase mask. The optical symmetry transformation translates off-axis plane waves into focusing spots of different transverse shifts on a focal plane and thus offers a novel design paradigm for single metalens-based extreme field-of-view (FOV) imaging 48 , 51 , 52 and wide-angle beam-steering antennas 49 , 50 . Fig.…”
With inherent orthogonality, both the spin angular momentum (SAM) and orbital angular momentum (OAM) of photons have been utilized to expand the dimensions of quantum information, optical communications, and information processing, wherein simultaneous detection of SAMs and OAMs with a single element and a single-shot measurement is highly anticipated. Here, a single azimuthal-quadratic phase metasurface-based photonic momentum transformation (PMT) is illustrated and utilized for vortex recognition. Since different vortices are converted into focusing patterns with distinct azimuthal coordinates on a transverse plane through PMT, OAMs within a large mode space can be determined through a single-shot measurement. Moreover, spin-controlled dual-functional PMTs are proposed for simultaneous SAM and OAM sorting, which is implemented by a single spin-decoupled metasurface that merges both the geometric phase and dynamic phase. Interestingly, our proposed method can detect vectorial vortices with both phase and polarization singularities, as well as superimposed vortices with a certain interval step. Experimental results obtained at several wavelengths in the visible band exhibit good agreement with the numerical modeling. With the merits of ultracompact device size, simple optical configuration, and prominent vortex recognition ability, our approach may underpin the development of integrated and high-dimensional optical and quantum systems.
“…1 , the optical symmetry transformation is performed through a single radial-quadratic phase mask ( ), which is mathematically expressed as 48 : where k 0 is the wavevector in free space, θ is the oblique angle of the incident light, and f is the focal length of the phase mask. The optical symmetry transformation translates off-axis plane waves into focusing spots of different transverse shifts on a focal plane and thus offers a novel design paradigm for single metalens-based extreme field-of-view (FOV) imaging 48 , 51 , 52 and wide-angle beam-steering antennas 49 , 50 . Fig.…”
With inherent orthogonality, both the spin angular momentum (SAM) and orbital angular momentum (OAM) of photons have been utilized to expand the dimensions of quantum information, optical communications, and information processing, wherein simultaneous detection of SAMs and OAMs with a single element and a single-shot measurement is highly anticipated. Here, a single azimuthal-quadratic phase metasurface-based photonic momentum transformation (PMT) is illustrated and utilized for vortex recognition. Since different vortices are converted into focusing patterns with distinct azimuthal coordinates on a transverse plane through PMT, OAMs within a large mode space can be determined through a single-shot measurement. Moreover, spin-controlled dual-functional PMTs are proposed for simultaneous SAM and OAM sorting, which is implemented by a single spin-decoupled metasurface that merges both the geometric phase and dynamic phase. Interestingly, our proposed method can detect vectorial vortices with both phase and polarization singularities, as well as superimposed vortices with a certain interval step. Experimental results obtained at several wavelengths in the visible band exhibit good agreement with the numerical modeling. With the merits of ultracompact device size, simple optical configuration, and prominent vortex recognition ability, our approach may underpin the development of integrated and high-dimensional optical and quantum systems.
“…One merit of catenary structures over traditional discrete metasurfaces is the quasicontinuous phase profile; thus, a much larger phase gradient is possible. As demonstrated recently, [ 58,142,167,174,175 ] such phase distributions make these metasurfaces function as wide‐angle Fourier transforming lenses. Assuming that the collimated incident light beam lies in the xz ‐plane with an arbitrary angle of θ to the normal axis of a quadratic lens, the phase carried by the outgoing light would be where k 0 x sinθ is the gradient phase induced by the oblique incidence.…”
Section: Catenary Structures For Photonic Spin–orbit Interactionmentioning
with the development of nanofabrication, characterization, and numerical modeling techniques, research has focused on optical applications in the subwavelength region, where the characteristic dimension of light-matter interactions is below the operating wavelength. [7,8] It was found that catenary functions have played more important roles in this new realm. [9] First, the coupling of evanescent waves, such as surface plasmon polaritons (SPPs) leads to catenary-shaped intensity distributions, [10,11] which have found practical applications in super-resolution imaging and lithography. [12-15] Second, catenaryshaped subwavelength structures have been proved to be ideal candidates for generating geometric phases, which are widely utilized to construct various functional metasurfaces. [2,16-18] Furthermore, besides the field intensity distribution, the dispersion curves of many capacitive metasurfaces were found to be characterized by the catenary function, [3] which provides a versatile mathematical-physical model to predict the optical and electromagnetic properties of metasurfaces. The application of mathematical functions in classical optical problems is a well-established phenomenon. For instance, in geometric optics governed by Fermat's principle and Snell's law, the surfaces of lenses and mirrors have spherical, parabolic, or aspherical shapes to focus light on a given spot. In laser optics, the characteristics of laser beams are characterized by mathematical functions, such as the Gaussian function, Bessel function, Airy function, and Hermite and Laguerre polynomials. [19-21] In addition, the dispersion curve of an anisotropic material is described by an ellipse. If one of the dielectric tensors were to become negative, the dispersion curve would become hyperbolic. Such materials are therefore called hyperbolic materials. [22,23] Because of the unusual dispersion curve, hyperbolic materials could be used in super-resolution imaging as well as enhancement of spontaneous emission. In this review, we focus on the applications of catenary functions in optics and electromagnetics. There are two types of catenary functions, the hyperbolic cosine function (ordinary catenary) and the logarithmic cosine function, which is often called catenary of equal strength. [1] As shown in Figure 1, both curves resemble the parabolic curve for vanishingly small x values. As x increases, the discrepancy increases and the slope of the catenary of equal strength is the largest among the three curves. Like the parabola, both types of catenary functions Catenary functions play pivotal roles in describing the electromagnetic vectors, intensity distribution, and dispersion of structured light on the subwavelength scale. In this article, the history, basic theories, functional devices, and applications of catenary functions in optics and electromagnetics are reviewed. First, the catenary fields generated by the coupling of evanescent waves are discussed, together with their applications in flat optics, super-resolution imaging, and lith...
“…Crystalline silicon (c‐Si) appears as a natural choice, [ 11,13,36,22–24,31–35 ] as it is a high index material that is available at high quality and compatible with CMOS processes, which is important for scale‐up manufacturing. Different optimization methods have already been used to reduce the impact of silicon absorption on metasurface performance.…”
Section: Introductionmentioning
confidence: 99%
“…[ 23,24 ] The high index of silicon has also enabled the first demonstration of a metalens with a field of view as high as ±89°. [ 36 ] The question is whether this performance can be improved even further and made comparable with that achieved in TiO 2 , which has demonstrated multiple functionalities and an efficiency up to η ≈ 90%. In order to answer this question, we have identified a metasurface design strategy that is more tolerant to absorption losses, thus paving the way to the highest efficiency operation also in crystalline silicon.…”
Dielectric metasurfaces have significant potential for delivering miniaturized optical systems with versatile functionalities, leading to applications in various fields such as orbital angular momentum generation, imaging, and holography. Among the different materials, crystalline silicon has the advantage of technological maturity and high refractive index, which increases design flexibility and processing latitude. The second, and often overlooked, advantage of silicon is that it affords embedding the metasurface in a protective material such as silica, which is essential for practical applications. The trade‐off against this high refractive index is silicon's absorption at visible wavelength, which requires new design strategies. Here, such a strategy based on metasurfaces supporting air modes is identified that can lead to a transmission efficiency as high as 87% at a wavelength of 532 nm. This exceptional efficiency is obtained by using the high index to confine the electric field in the periphery of the meta‐atoms, thereby reducing absorption losses. As an example, the design of a fully embedded metasurface is described that can generate vortex beams with various orders of orbital angular momentum. It is envisioned that the proposed strategy paves the way for practical applications of high‐efficiency metasurfaces based on crystalline silicon.
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