A review of dielectric optical metasurfaces for spatial differentiation and edge detection

doi:10.1007/s12200-021-1124-5

Front. Optoelectron.

2021, Vol. 14

Issue (2) : 187-200 https://doi.org/10.1007/s12200-021-1124-5

REVIEW ARTICLE

A review of dielectric optical metasurfaces for spatial differentiation and edge detection

Lei WAN^1,^2,^3,⁴(

), Danping PAN¹, Tianhua FENG^1,³(

), Weiping LIU^1,⁴, Alexander A. POTAPOV^3,⁵

¹. Department of Electronic Engineering, College of Information Science and Technology, Jinan University, Guangzhou 510632, China
². Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
³. JNU-IREE RAS Joint Laboratory of Information Techniques and Fractal Signal Processing, Jinan University, Guangzhou 510632, China
⁴. Key Laboratory of Optoelectronic Information and Sensing Technologies of Guangdong Higher Education Institutes, Jinan University, Guangzhou 510632, China
⁵. Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow 125009, Russia

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Abstract

Dielectric metasurfaces-based planar optical spatial differentiator and edge detection have recently been proposed to play an important role in the parallel and fast image processing technology. With the development of dielectric metasurfaces of different geometries and resonance mechanisms, diverse on-chip spatial differentiators have been proposed by tailoring the dispersion characteristics of subwavelength structures. This review focuses on the basic principles and characteristic parameters of dielectric metasurfaces as first- and second-order spatial differentiators realized via the Green’s function approach. The spatial bandwidth and polarization dependence are emphasized as key properties by comparing the optical transfer functions of metasurfaces for different incident wavevectors and polarizations. To present the operational capabilities of a two-dimensional spatial differentiator in image information acquisition, edge detection is described to illustrate the practicability of the device. As an application example, experimental demonstrations of edge detection for different biological cells and a flower mold are discussed, in which a spatial differentiator and objective lens or camera are integrated in three optical pathway configurations. The realization of spatial differentiators and edge detection with dielectric metasurfaces provides new opportunities for ultrafast information identification in biological imaging and machine vision.

Keywords dielectric metasurfaces spatial differentiator edge detection optical transfer function

Corresponding Author(s): Lei WAN,Tianhua FENG

Just Accepted Date: 08 January 2021 Online First Date: 05 February 2021 Issue Date: 14 July 2021

Cite this article:

Lei WAN,Danping PAN,Tianhua FENG, et al. A review of dielectric optical metasurfaces for spatial differentiation and edge detection[J]. Front. Optoelectron., 2021, 14(2): 187-200.

URL:

https://academic.hep.com.cn/foe/EN/10.1007/s12200-021-1124-5
https://academic.hep.com.cn/foe/EN/Y2021/V14/I2/187

Fig.1 Basic principle of spatial differentiation and edge detection with metamaterials and metasurfaces. (a) Fourier information of the input signal can be obtained by a block with the Fourier transform (FT) function. After passing through the metasurface, the output signal can be obtained with the inverse Fourier transform (IFT) operation. (b) Graded index (GRIN) metamaterials can be employed to realize the FT and IFT. Reprinted with permission from Ref. [51]. Copyright 2013, The Optical Society of America. (c) Practical realization of the configuration. Reprinted with permission from Ref. [6]. Copyright 2014, American Association for the Advancement of Science

Fig.2 (a) Schematic of an isotropic second-order spatial differentiator realized by a photonic crystal slab and a separate dielectric slab. (b) Optical transfer functions (OTFs) of the device for the s wave, (c) p wave, and (d) unpolarized light. (e) One-dimensional (1D) OTF as a function of the wavevector and the corresponding quadratic fitting. (f) Morphologies of the incident Stanford emblem and slot patterns (left column) and the corresponding edge images (right column). Reproduced with permission from Ref. [53]. Copyright 2018, The Optical Society of America

Fig.3 (a) Schematic of the second-order spatial differentiator based on nonlocal metasurfaces consisting of split-ring resonators. (b) Evolution of transmission curves of the metasurface-based spatial differentiator with an increasing incident angle from 0° to 45°. (c) Output results of an ideal second-order differentiation operation and of the nonlocal metasurface corresponding to a sinusoidal function input. (d) Two-dimensional (2D) OTF of the differentiator as a function of incident angle q. (e) Results of edge detection corresponding to x-polarized wave illumination and (f) y-polarized wave illumination. Reproduced with permission from Ref. [36]. Copyright 2018, The Physical Society of America

Fig.4 (a) Schematic of the first-order spatial differentiator based on the reflective dielectric metasurface. (b) Magnetic field profiles at the x-z and x-y planes, respectively. (c) 1D OTF of the first-order spatial differentiator corresponding to changes of reflection amplitude and phase for the transverse-magnetic (TM) polarization light incidence. (d) Output intensity curve of the metasurface and the theoretically calculated results corresponding to the input Gaussian signal. (e) Incident image consisting of “ZJU” letters. (f) Reflected edge detection image corresponding to (e). Reproduced with permission from Ref. [46]. Copyright 2020, John Wiley & Sons Inc

Fig.5 (a) Unit cell of the second-order spatial differentiator based on the hole dielectric metasurface. (b) Fano transmission curves of the spatial differentiator as functions of an incident angle from 0° to 25°. 2D OTFs of device corresponding to (c) s-polarized and (d) p-polarized wave incidence. The output result of edge detection of (e) a 2D input image based on the second-order spatial differentiator for x-polarized light illumination. Reproduced with permission from Ref. [62]. Copyright 2020, The Chemical Society of America

Fig.6 (a) Schematic of the second-order spatial differentiator consisting of a silicon nanodisk metasurface. (b) Scattered power of the electric and magnetic dipole resonances as functions of wavelength for different incident angles from 0° to 25°. 2D OTFs of the device corresponding to the (c) s-polarized wave and (d) p-polarized wave incidence. The output images for edge detection for (e) x-polarized and (f) unpolarized light illumination. Reproduced with permission from Ref. [48]. Copyright 2020, The Optical Society of America

Fig.7 (a) Schematic of a second-order spatial differentiator consisting of a silicon nanorod array, and the corresponding scanning electron microscope (SEM) image. (b) Measurement results and fitted parabolic curve of the 1D OTF as a function of numerical aperture (NA). (c) Edge detection images using a resolution test chart with the differentiator under unpolarized light illumination of 1120 nm. Optical pathway configurations corresponding to the differentiators integrated in the front of (d) an objective lens, in the front of (e) a commercial charge-coupled device camera, and in the back of (f) a metalens. Target edge images of (g), (h) a biological cell and (i) a plastic flower mold with a 2D spatial differentiator corresponding to the three types of optical pathway configurations. Reproduced with permission from Ref. [47]. Copyright 2020, The Nature Publishing Group

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