Analog Optical Spatial Differentiators Based on Dielectric Metasurfaces

Abstract

Analog spatial differentiator is an important optical computational device that can be potentially used in the field of high‐speed edge detection and optical image processing. In the current stage, a general method is still required to robustly design compact devices for various spectrum or complex situation. In this work, a dielectric metasurface method is proposed and experimentally demonstrated to build optical spatial differentiators. This is physically realized by a high‐quality magnetic resonance mode that is hybridized with the classic bounded surface wave via grating coupling. Experimentally, a well‐defined first‐order differentiation effect is observed at oblique light incidence. The application potential of this device is evaluated by inputting various figures. It is shown that it can perform an optical processor to trace the profiles of the figure content with a resolution better than 30.8 µm. This work may pave a robust way to build ultracompact optical computation devices for real‐time image processors, which can be freely extended to various frequencies.

Meta-optics for spatial optical analog computing

“…In the GF approach, the desired optical transfer function is directly implemented into the wave vector domain (Fourier or k-space) by using the nonlocal (angular dependent) response of a suitably designed metamaterial or metasurface as shown in Figure 1B [47][48][49][50][51]. Due to the direct implementation of the desired transfer function in this method, performing Fourier/inverse Fourier transforms is no longer needed, which in turn leads to the reduction in the overall structure size [34].…”

“…Several other proposals and demonstrations using spin Hall effect (SHE) of light [65], prism coupling configuration [66], reflective hybrid plasmonic-dielectric metasurfaces [48], periodic plasmonic metasurfaces covered by graphene [67], multiinput-multioutput computational metasurfaces [68], ultrathin bianisotropic metasurfaces [69], polarization-insensitive structured surfaces with tailored nonlocality [70], and engineering the spatial dispersion of the electric dipole resonance in dielectric metasurfaces [71] to perform mathematical operators based on GF approach have been reported in the literature.…”

Phase-controlled metasurface design via optimized genetic algorithm

“…The special output light beams can be freely harnessed by the phase discontinuity serving as a degree of freedom that can be engineered by the artificial periodic structures of optical metasurface. In the last decade, the continuous development of nanofabrication technologies was the main driving impetus that has advanced and enriched the bourgeoning research field of optical metasurfaces, triggering plethora of applications such as optical metalens [2][3][4][5][6][7][8][9], beam splitter [10][11][12], integrator [13][14][15], differentiator [13,[15][16][17], Stokes parameters extractors [18][19][20], hologram [10,[21][22][23][24][25][26][27][28], special light beam generators [10,[29][30][31][32][33][34][35][36][37][38], and etc. Among all the diverse metasurfaces, the optical PB phase metasurfaces have attracted more and more interests of scientists owing to their high degrees of freedom by easily rotating the orientation of the unit cells, and their high conversion efficiency due to the low dielectric loss [2,…”

Monolithic metasurface spatial differentiator enabled by asymmetric photonic spin-orbit interactions

“…The most important process for edge detection is differentiation, a process generally operated by a spatial differentiator, either in a digital computation or an analog computation way [5][6][7]. Compared with digital computing, optical analog computing can process parallel information with high efficient and low power consumption, holding great potential in real-time detections [8][9][10][11]. However, in the traditional optical computing system, a 4-F optical system containing at least two lenses and a spatial filter is required for Fourier transform and inverse Fourier transform, which is bulky and complicated, hindering the applications in modern optoelectronics with high integration level.…”

“…However, additional prisms or lenses are still required for plasmon coupling or Fourier transform in those applications [37,40], which is incompatible with the flat and compact optical systems. Besides, many metasurface spatial differentiators work only in 1D edge detection [8,9,35,36], restricting the practical applications in image recognition and processing.…”