Optical modulator based on the coupling effect of different surface plasmon modes excited on the metasurface

D. Wei, C. Hu, M. Chen, J. Shi, J. Luo, X. Zhang, H. Wang, and C. Xie

Optics Materials Express, 10, 105 (2020)
An optical modulator of a metasurface constructed by an arrayed nano-ridge-aperture with a central nano-cylinder (NRANC) is designed and fabricated. The coupling effect between the localized surface plasmons (LSPs) distributed over each nano-apex of the nano-ridge-aperture and the outer-edge of the central nano-cylinder, and the surface plasmons polaritons (SPPs) generated over the periodic metasurface, have been investigated carefully. The tapered structure can be utilized to concentrate the incident energy and also remarkably enhance the localized light-field. The electrical dipolar induced on the tapered structure will regulate the reflectance or transmission characters. The coupling effect of the LSPs formed over the NRANC will lead to an enhancement of the induced surface electrical dipolar and further regulate the optical properties of the NRANC. By varying the geometrical parameters of the metasurface, the resonance frequency of the LSPs mode can also be adjusted and the movement of transmittance peak can be viewed, and the enhancement factor would reach as large as 1.4×103. The coupling between the LSPs and SPPs would stimulate Fano resonance. Adjusting the incidence angle of illuminating lasers in the visible and infrared ranges could modulate the stimulation of SPPs, so as to induce a relatively large alteration on the transmittance spectral. Through performing the near-field optical measurements, the near-field optical characteristic including the surface induced charge information can be viewed, and a small (∼96 nm at x-direction) and bright hot-spot is already observed under 45° oblique incidence of 633 nm TM lasers. The metasurface of constructed NRANC highlights several potential applications such as color filter, reflective reflectors, surface enhanced Raman.