Transmission phase control by stacked metal-dielectric hole array with two-dimensional geometric design

Wavefront Control with Nanohole Array-Based Out-of-Plane Metasurfaces

Planar metasurfaces provide exceptional wavefront manipulation at the subwavelength scale by controlling the phase of the light. Here, we introduce an out-of-plane nanohole-based metasurface design with the implementation of a unique self-rolling technique. The photoresist-based technique enables the fabrication of the metasurface formed by nanohole arrays on gold (Au) and silicon dioxide (SiO₂) rolled-up microtubes. The curved nature of the tube allows the fabrication of an out-of-plane metasurface that can effectively control the wavefront compared to the common planar counterparts. This effect is verified by the spectral measurements of the fabricated samples. In addition, we analytically calculated the dispersion relation to identify the resonance wavelength of the structure and numerically calculate the phase of the transmitted light through the holes with different sizes. Our work forms the basis for the unique platform to introduce a new feature to the metasurfaces, which may find many applications from stacked metasurface layers to optical trapping particles inside the tube.

Tunable enhanced 0th-order transmission in a metal-dielectric hole array covered with a subwavelength liquid crystal layer

We demonstrate tunable, enhanced 0th-order transmission through a metal-dielectric nanohole array device with a subwavelength-thick liquid crystal (LC) layer. The LC filled the nanoholes and formed a subwavelength covering layer, which is then capped by a top cover layer. The wavelength where the transmittance dip associated with the LC occurs is determined by the anisotropic refractive-index component of the LC, which is normal to the surface of the hole array. A low-refractive-index cover layer suppresses unwanted higher-order diffraction, which results in an enhancement of the 0th-order transmission, which is closely related to laterally propagating surface plasmon polaritons. The proposed design is expected to help realize tunable plasmonic devices with high optical transmittance.

Highly efficient beam steering with a transparent metasurface

We propose an ultra-thin planar metasurface with phase discontinuities for highly efficient beam steering. The effect benefits from the broadband transparency and flexible phase modulation of stacked metal/dielectric multi-layers that is perforated with coaxial annular apertures. Proof-of-principle experiments verify that an efficiency of 65% and a deflection angle of 18° at 10 GHz are achieved for the transmitted beam, which are also in good agreement with the finite-difference-method-in-time-domain (FDTD) simulations. The scheme shall be general for the design of beam-steering transmitters in all frequencies.

Wavefront control by stacked metal-dielectric hole array with variable hole shapes

A stacked metal-dielectric hole array (SHA) containing rectangular holes whose shape gradually varies in-plane is proposed as a means of achieving wavefront control. The dependence of the transmitted phase on the frequency can be tuned by the hole shape, in particular the length of the sides that are normal to the incident polarization. The combination of periodic holes along the polarization direction and the gradual change in hole shape normal to the polarization direction produce an inclined wavefront for 1-dimensional beam steering. An in-plane phase difference of 0.6π using an SHA with a thickness of one-sixth of the wavelength has been experimentally demonstrated.