Near Unity Transmission and Full Phase Control with Huygens' Dielectric Metasurfaces based on Cuboid Shape Silicon Nanoresonators

1.IntroductionIn resonant dielectric nanostructures, the simultaneous excitation and interference of magnetic and electric dipole resonances enables the suppression of backward scattering. The nanostructures then act as ideal... [ view full abstract ]

1.Introduction

In resonant dielectric nanostructures, the simultaneous excitation and interference of magnetic and electric dipole resonances enables the suppression of backward scattering. The nanostructures then act as ideal Huygens’ sources for which the phase of re-emitted light can be controlled by the actual phase of induced dipoles. The transmission and phase shift can be tailored by the nanostructure geometry. So far, disks and square prisms are most widely investigated. Although transmission T > 80% with full 2π phase control has been achieved, it is difficult to reach T≈100% over the whole range of phases for fixed thickness and periodicity. Here we show that, using cuboidal nanostructures, another degree of freedom is available to tune their optical performance, allowing improved resonance overlapping and T≥95% in 2π range of phase-shifts.

2. Method

We investigate both theoretically and experimentally the transmission and phase shift obtained, under normal incidence illumination, with arrays of Silicon cuboids as a function of their lateral size along the polarization direction while keeping its size along the orthogonal direction and the array period fixed (Figure 1). The transmission and phase shift performance of the fabricated structures is characterized using a beam bending configuration and an 8-level computer generated hologram (CGH).

3. Results and Discussion

Figure 2 shows the simulated transmission and phase shift obtained for different sizes of cuboidal particle along the polarization direction at operating wavelength λ=800nm. The particle height is around λ/6. As seen, T>95% can be obtained for the whole range of 2p phase shift, which is due to perfect overlap and simultaneous spectral shift of the electric and magnetic resonances, as revealed by a multipole decomposition analysis (Figure 3).  Using this configuration we designed gradient metasurfaces composed of 8 (and 12) elements for which 63% (71%) of the total transmitted light is deflected into the desired order. We also demonstrated broadband CGH, which was experimentally reconstructed using a supercontinuum laser with wavelength spanning from near IR to visible frequencies (Figure 4). The highest experimental diffraction efficiency of 72.8% of the total transmitted light was achieved at a wavelength of 770nm.