A review of dielectric optical metasurfaces for wavefront control

Abstract

During the past few years, metasurfaces have been used to demonstrate optical elements and systems with capabilities that surpass those of conventional diffractive optics. Here we review some of these recent developments with a focus on dielectric structures for shaping optical wavefronts. We discuss the mechanisms for achieving steep phase gradients with high efficiency, simultaneous polarization and phase control, controlling the chromatic dispersion, and controlling the angular response. Then we review applications in imaging, conformal optics, tunable devices, and optical systems. We conclude with an outlook on future potentials and challenges that need to be overcome. A. High-efficiency high-gradient phase controlSince high-contrast transmitarrays (HCA) are central to the most of the discussions of this section, we first briefly discuss their operation. We are primarily interested in the two-dimensional HCAs, and therefore we consider their case here, although much of the discussions are also valid for the one-dimensional case. In general, these devices are based on high-refractive-index dielectric nano-scatterers surrounded by low-index media [13, 38, 65, 67, 70-72, 76, 78]. The structure can be symmetric (i.e., with the substrate and capping layers having the same refractive indexes) [36] or asymmetric [66,67,76,78]. Depending on the materials and the required phase coverage, the thickness of the high-index layer is usually between 0.5λ 0 and λ 0 , where λ 0 is the free space wavelength. Typically, these structures are designed to be compatible with conventional microfabrication techniques;

Computational inverse design for cascaded systems of metasurface optics

“…It is desirable that this iterative optimization be performed using the steepest-descent algorithm [65]. At each step of the optimization, the design parameters are updated using the following rule: (2) 6 Each vector of design parameters is adjusted by the gradient m dC dw , scaled by a predefined step-size  . The difficulty associated with this approach is the requirement that the gradient be computed efficiently, since each m w may contain thousands or millions of design variables.…”

“…Optical metasurfaces are composite structures that utilize nanoscale patterning to achieve properties not found in nature [1,2]. By tailoring the dimensions of nanoscale scattering elements (meta-atoms) arranged in a periodic lattice, it is possible to precisely shape the wavefronts (phase) of incident light (see Fig.…”

Modeling Metasurfaces Using Discrete-Space Impulse Response Technique

“…where f in (n) = F in (nΛ), and F out (x) can be reconstructed from f out (n) according to (2). Equation…”

“…Therefore, approximate methods are commonly used for their design and analysis. Aperiodic metasurfaces with periodic lattices are a significant category of metasurfaces because of the ease of their designs, and a large number of components based on such metasurfaces have been demonstrated at microwave and optical frequencies [1,2,[8][9][10][11][12][13]. Figure 1a shows a schematic illustration of an aperiodic metasurface with a periodic lattice.…”

Single-layer Planar Metasurface Lens with >170° Field of View

“…components [5][6][7][8][9][10][11][12][13][14] . Metasurface-based designs have been widely employed for constructing planar ultra-thin lenses, also called metalenses [15][16][17][18][19][20][21][22] , to mitigate several types of aberrations 23 , in particular spherical 16 and chromatic [24][25][26][27] aberrations.…”