Abstract
AbstractNonlinear Pancharatnam–Berry phase metasurfaces facilitate the nontrivial phase modulation for frequency conversion processes by leveraging photon‐spin dependent nonlinear geometric‐phases. However, plasmonic metasurfaces show some severe limitation for nonlinear frequency conversion due to the intrinsic high ohmic loss and low damage threshold of plasmonic nanostructures. Here, the nonlinear geometric‐phases associated with the third‐harmonic generation process occurring in all‐dielectric metasurfaces is studied systematically, which are composed of silicon nanofins with different in‐plane rotational symmetries. It is found that the wave coupling among different field components of the resonant fundamental field gives rise to the appearance of different nonlinear geometric‐phases of the generated third‐harmonic signals. The experimental observations of the nonlinear beam steering and nonlinear holography realized in this work by all‐dielectric geometric‐phase metasurfaces are well explained with the developed theory. This work offers a new physical picture to understand the nonlinear optical process occurring at nanoscale dielectric resonators and will help in the design of nonlinear metasurfaces with tailored phase properties.
Highlights
We theoretically and experimentally study the nonlinear geometric-phases associated with the third-harmonic generation (THG) process occurring in all-dielectric metasurfaces, which are composed of silicon nanofins with different in-plane rotational symmetries
The nonlinear optical process occurring in dielectric nanostructures will inevitably involve the wave coupling among different field components of the resonant fundamental wave (FW), and the radiated nonlinear waves can carry additional geometric-phases beyond what has been predicted in their plasmonic counterpart
We show that the dielectric nanofin structures with C1, C2, and C4 in-plane rotational symmetry generate circularly polarized TH signals in forward direction carrying the geometric-phases as predicted by the selection rule for nonlinear processes
Summary
Optical metasurfaces offer the ultimate solution for modern diffractive optical elements design by leveraging the artificially tailored nanostructures of subwavelength geometries, which facilitate the flexible control of the phase, amplitude, and polarization of the light with an ultra-compact profile.[1,2] Since the propagation of the light is substantially determined by the local phase distribution of the wavefront, metasurface structures with full-phase transmitted or reflected phase discontinuities are highly desired for realizing numerous optical functionalities.[3,4,5,6,7,8] In particular, Pancharatnam-Berry phase or geometric-phase metasurfaces simplify the optical wavefront engineering by utilizing the linear Pancharatnam-Berry phase, which can be precisely controlled by locally rotating the nanostructures.[9,10,11,12] At the very beginning, plasmonic metasurfaces gained its popularity for the simplicity of obtaining an effective electric and magnetic response with spatially tailored induced surface currents.[13]. The pioneering work that takes advantage of the hybrid metasurfaces based on plasmonic structures and multiple-quantum-wells in semiconductors reveals the possibility of exploiting the spatially varied nonlinear geometric-phase for advanced nonlinear wavefront control with high-efficiency.[31,32,33] In addition, by revisiting the selection rule that holds for the nonlinear crystals, it was revealed that plasmonic nanostructures with specific structural symmetry show similar selection behavior for the harmonic generation processes.[34,35,36,37,38] In nonlinear geometric-phase metasurfaces, recently reported works mostly focusses on implementing plasmonic nanostructures while studies on all-dielectric nonlinear geometric-phase metasurfaces are still missing. We theoretically and experimentally study the nonlinear geometric-phases associated with the third-harmonic generation (THG) process occurring in all-dielectric metasurfaces, which are composed of silicon nanofins with different in-plane rotational symmetries. Based on the full-wave simulation and experimental measurements, we test our theoretical analysis by realizing nonlinear beam steering and nonlinear holography based on such metasurfaces
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