![]() ![]() Separate optimization of small portions of a gradient metasurface and then assembling them together to form a large metalens has been proposed 14, 27 however, the effect of discontinuities at the boundaries of patches has not been considered and efficient high-NA metasurfaces based on such approaches have not been demonstrated yet. The metasurfaces designed based on iterative adjoint optimization techniques can be efficient 16, 18, 19, 20 however, their dimensions are inevitably limited by the available computational resources because the optimization process requires full-wave simulation of the entire device in each iteration, or simulation and optimization of each zone of the device 25 that is applicable to metalenses but cannot be readily extended to general holograms. Several approaches have been proposed for designing efficient high-NA metasurfaces including adjoint optimization 16, 18, 19, 20, 25, 26 and patching together separately designed gratings 14, 27. However, the efficiency of metasurfaces is known to decrease with increasing NA, resulting in a trade-off between the NA and efficiency 11, 22, 23, 24. As a result, increasing the efficiency of metasurfaces has been the subject of recent studies 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and low numerical aperture (NA) metasurface components (i.e., metasurfaces with small deflection angles) with efficiencies of more than 97% have been reported 21. Used either as single-layer devices or as integral parts of cascaded metasurface systems, one of the main requirements for metasurfaces is high efficiency. The planar form factor of metasurfaces and the high multilayer overlay accuracy of the semiconductor manufacturing process enable the implementation of low-cost monolithic optical systems composed of cascaded metasurfaces whose production does not involve post-fabrication assembly and alignment steps 9, 10. Similar content being viewed by othersįlat optical devices based on dielectric metasurfaces have recently attracted significant attention due to their small size, low weight, and the potential for their low-cost manufacturing using semiconductor fabrication techniques 1, 2, 3, 4, 5, 6, 7, 8. The grating averaging is a versatile technique applicable to many types of gradient metasurfaces, thus enabling highly efficient metasurface components and systems. Using this technique, we identify an unconventional metasurface design and experimentally demonstrate a metalens with a numerical aperture of 0.78 and a measured focusing efficiency of 77%. Unlike optimization-based methods that rely on full-wave simulations and are only practicable in designing small metasurfaces, the gradient averaging technique allows for the design of arbitrarily large metasurfaces. The technique is based on a particular coherent averaging of diffraction coefficients of periodic blazed gratings and can be used to compare the performance of different metasurface designs in implementing high numerical aperture devices. Here we introduce and apply a technique for the estimation of the efficiency of high numerical aperture metasurfaces. However, metasurfaces are conventionally designed using approaches that are optimal for small deflection angles and their performance for designing high numerical aperture devices is not well quantified. This is often the case when biphenyl is at room temperature.One of the important advantages of optical metasurfaces over conventional diffractive optical elements is their capability to efficiently deflect light by large angles. ![]() Main reflections are usually stronger in intensity and span a lattice defined by three-dimensional reciprocal lattice vectors ( a ∗, b ∗, c ∗ ) -electron effect which favors coplanarity of the two planes. ![]() The diffraction patterns of aperiodic crystals contain two sets of peaks, which include "main reflections" and "satellite reflections". They are classified into three different categories: incommensurate modulated structures, incommensurate composite structures, and quasicrystals. In other words, they are periodic crystals in higher dimensions. Crystal type lacking 3D periodicity Reciprocal SpaceĪperiodic crystals lack three-dimensional translational symmetry but still exhibit three-dimensional long-range order. ![]()
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