Broadband and Arbitrary Linear Polarization Rotation via Coherent Control in a Subwavelength Plasmonic Nano-Scatterer

Abstract

Manipulating light polarization at the subwavelength scale is critical for high-density photonic integration. Here, broadband and arbitrary linear polarization rotation is demonstrated in a subwavelength plasmonic nano-scatterer (0.22λ² at λ = 600 nm), consisting of two orthogonal metallic nanogroove antennas. This rotation is achieved by varying the phase difference between two counter-propagating surface plasmon polaritons (SPPs). The proposed approach exploits the intrinsic binary-phase and cosine-amplitude distributions of the SPP standing waves. The binary-phase distribution restricts the relative phase of orthogonal scattering components radiated from the two nanogrooves to 0 or π, ensuring high-purity linear polarization. The cosine-amplitude distribution modulates their power ratio to rotate the polarization angle of the total scattered light. Therefore, the linear polarization of the total scattered light is arbitrarily rotated (Δα = 180°) by only changing the phase difference between two incident SPPs with parallel linear polarization. Experimentally, an ultrasmall nano-scatterer (0.22λ² at λ = 600 nm) is fabricated. At λ = 550 nm, 600 nm, and 650 nm, it is demonstrated that the polarization angle α is arbitrarily rotated from 90° to − 90° with a degree of linear polarization (D_p > 0.82).