Abstract
Abstract In an optical Pancharatnam-Berry (PB) phase metasurface, each sub-wavelength dielectric structure of varied spatial orientation can be treated as a point source with the same amplitude yet varied relative phase. In this work, we introduce an optimized genetic algorithm (GA) method for the synthesis of one-dimensional (1D) PB phase-controlled dielectric metasurfaces by seeking for optimized phase profile solutions, which differs from previously reported amplitude-controlled GA method only applicable to generate transverse optical modes with plasmonic metasurfaces. The GA–optimized phase profiles can be readily used to construct dielectric metasurfaces with improved functionalities. The loop of phase-controlled GA consists of initialization, random mutation, screened evolution, and duplication. Here random mutation is realized by changing the phase of each unit cell, and this process should be efficient to obtain enough mutations to drive the whole GA process under supervision of appropriate mutation boundary. A well-chosen fitness function ensures the right direction of screened evolution, and the duplication process guarantees an equilibrated number of generated light patterns. Importantly, we optimize the GA loop by introducing a multi-step hierarchical mutation process to break local optimum limits. We demonstrate the validity of our optimized GA method by generating longitudinal optical modes (i. e., non-diffractive light sheets) with 1D PB phase dielectric metasurfaces having non-analytical counter-intuitive phase profiles. The produced large-area, long-distance light sheets could be used for realizing high-speed, low-noise light-sheet microscopy. Additionally, a simplified 3D light pattern generated by a 2D PB phase metasurface further reveals the potential of our optimized GA method for manipulating truly 3D light fields.
Highlights
Optical metasurface, an optically thin layer consisting of sub-wavelength plasmonic or dielectric structures, is capable of tailoring the wave front of the outgoing light waves by introducing an abrupt phase discontinuity in the transverse plane, deflects the incident light in a customized angle owing to the generalized Snell’s law [1]
We introduce an optimized genetic algorithm (GA) method for the synthesis of one-dimensional (1D) PB phase-controlled dielectric metasurfaces by seeking for optimized phase profile solutions, which differs from previously reported amplitude-controlled GA method only applicable to generate transverse optical modes with plasmonic metasurfaces
Distinct from the amplitude-controlled GA investigated in Ref. [40,41,42,43,44,45,46,47,48,49] or the complex meta-dielectric resonance structures studied in Ref. [50,51,52,53,54,55,56], here, we address a new phase-controlled GA method targeting on-demand optical PB phase metasurface synthesis
Summary
An optically thin layer consisting of sub-wavelength plasmonic or dielectric structures, is capable of tailoring the wave front of the outgoing light waves by introducing an abrupt phase discontinuity in the transverse plane, deflects the incident light in a customized angle owing to the generalized Snell’s law [1]. 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 rotating the orientation of the unit cells, and their high conversion efficiency due to the low dielectric loss [2, 3, 10, 23, 27, 38, 39]. Another advantage of optical PB phase metasurface is the identical optical. All the aforementioned conventional optical metasurfaces are designed on the basis of analytical solutions of specific optical modes, or by hologram method, so that the potential of the optical metasurfaces may be underestimated and might be further explored, e. g., by machine learning method
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