Plasmonic computing of spatial differentiation

Abstract

Optical analog computing offers high-throughput low-power-consumption operation for specialized computational tasks. Traditionally, optical analog computing in the spatial domain uses a bulky system of lenses and filters. Recent developments in metamaterials enable the miniaturization of such computing elements down to a subwavelength scale. However, the required metamaterial consists of a complex array of meta-atoms, and direct demonstration of image processing is challenging. Here, we show that the interference effects associated with surface plasmon excitations at a single metal–dielectric interface can perform spatial differentiation. And we experimentally demonstrate edge detection of an image without any Fourier lens. This work points to a simple yet powerful mechanism for optical analog computing at the nanoscale.

Analog Optical Spatial Differentiators Based on Dielectric Metasurfaces

“…The first‐order differentiation can be operated along the transverse direction. It could also work along the perpendicular direction by rotating the beam . Figure e plots the incident and reflected field profiles at the positions of the dotted lines in Figure c,d.…”

“…This result exactly reflects the optical computational feature of our device. By rotating the beam or the test sample, the edges of the ring along the x axis would also be detected due to the high symmetry of the metasurface structure. The second sample of “ZJU” letters was measured by the same setup (see Figure d,e).…”

“…There already exist a few potential application examples about metasurface‐based analog optical spatial devices such as differentiators, integrators, and even equation solvers . The artificial materials utilized in these studies could be classified into three categories: multilayer films, 1D gratings, and general 2D metasurfaces . Among these structures, the general 2D metasurfaces with strong modulation flexibility are widely employed to realize the desired spatial operation functions mathematically defined by different Green's functions.…”

“…For practice, simple structures are more preferable, for example by a single layer of resonant metasurface . As an important component for optical processing, the first‐order analog optical spatial differentiator has attracted special attentions . The practicability has been greatly improved in recent works.…”

“…The practicability has been greatly improved in recent works. In 2017, Zhu et al has experimentally realized such an optical differentiation device utilizing the angle sensitive excitation of surface plasmonic polariton on metal films . More recently, Bykov et al and Dong et al separately have showed the similar function using subwavelength gratings .…”