Polarization Generation and Manipulation Based on Nonlinear Plasmonic Metasurfaces

Abstract

along two orthogonal directions, single type of nanostructures have been tailored to convert linear polarization to circular polarization and even any polarizations through transmission, reflection, or scattering. [25][26][27][28][29] And two basic subunits that produce two orthogonal polarization components have also been applied to a similar metasurface polarization generator. [30,31] Recently, metasurfaces have been reported as various nonlinear light generation platforms [32] and the concept of wavefront control on metasurfaces has been successfully extended to the nonlinear regime. For example, a continuous control over the nonlinear phase change from 0 to 2π is recently realized by changing the size and shape of nanostructures, or rotating the elements with respect to the laboratory frame. Based on these mechanisms, nonlinear planar optical devices have been achieved with simultaneous harmonic generation and wavefront control. [33][34][35][36][37][38][39][40][41][42] However, so far, few works on polarization state control of nonlinear signals produced from nonlinear metasurfaces have been reported. The key issue is to find two orthogonal polarizations of harmonic components and introduce proper phase difference between them.Here, we demonstrate a nonlinear plasmonic metasurface to realize second harmonic generation (SHG) and polarization control of SH simultaneously. Split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) rotated by 90° are selected to generate orthogonal polarizations of SH components under the same linear polarized fundamental wave (FW), respectively. We find that phase difference and amplitude ratio between SH components can be tailored by adjusting the arm length of SRRs and CSRRs. By introducing spatial offset between adjacent basic supercells, we can achieve phase difference between two orthogonal components and thus realize polarization control of output SH emission and beam splitting at the same time. We then experimentally demonstrate a nonlinear metasurface that can simultaneously generate two separated SH beams with orthogonal circular polarizations under linearly polarized FW and two orthogonal linearly polarized SH beams under circularly polarized FW. Acting like a quarter-wave plate (QWP) in linear regime, the nonlinear metasurface is called an SH quarter-wave plate, which exhibits powerful capability of nonlinear polarization manipulation. Finally, we show various elliptical polarization generations for SH with proper design.Polarization is one of the most important properties of light, which is also a typical dimension for light field manipulation. With specially designed meta-atoms and tailorable phase distribution, metasurfaces have been employed to achieve arbitrary polarization state in linear regime. Moreover, metasurface is also a platform for various types of nonlinear light generation, which can be used to realize an integrated polarized light source combined with its powerful capability of polarization manipulation. Here, a nonlinear plasmonic ...

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