Programmable hyper-coded holography has the advantage of being programmable as well as being flexibly modifiable. Digitally coded metamaterials with excellent electromagnetic modulation capability and the ability to control the phase to modulate the spatial radiation field through external excitation in the form of switching can be used to realize low-cost digital arrays. We design a 1-bit encoded programmable metasurface, which is electrically connected to control the PIN diode in the switching state and to switch the condition of each metasurface cell between “0” and “1.” Using the designed programmable metasurface, we can randomly encode the cell structure to realize single-focus focusing, multi-focusing, and simple holographic letter imaging. Based on the nonlinear holographic model, we employ the Gerchberg-Saxton improvement algorithm to modulate the energy distribution at the focus by adjusting the phase distribution. Importantly, we introduce the Fourier convolution principle to regulate the holographic imaging focus flexibly.

Employing couplers to convert guided waves into free-space modes and flexibly control their wavefront is one of the key technologies in chip-integrated displays and communications. Traditional couplers are mainly composed of gratings, which have limitations in footprint, bandwidth, as well as controllability. Though the resonant/geometric metasurface newly emerges as a promising interface for bridging guided waves with free-space ones, it either relies on complex optimizations of multiple parameters, or is subject to the locked phase response of opposite spins, both of which hinder the functional diversity and practical multiplexing capability. Here, we propose and experimentally demonstrate an alternative with a spin-decoupled meta-coupler, simultaneously integrating triple functions of guided wave radiation, polarization demultiplexing, and dual-channel wavefront manipulation into a single device. By endowing polarization-dependent functionalities into a pure geometric metasurface, the out-coupled left-handed and right-handed circular polarization guided waves intelligently identify the predesigned phase modulation and reconstruct desired wavefronts, like bifocal focusing and holography multiplexing, with a polarization extinction ratio over 13.4 dB in experiments. We envision that the robust, broadband, and multifunctional meta-coupler could pave a way for the development of versatile multiplexed waveguide-based devices.

We propose and experimentally demonstrate a high quality (Q)-factor all-silicon bound state in the continuum (BIC) metasurface with an imperforated air-hole array. The metasurface supports two polarization-insensitive BICs originated from guided mode resonances (GMRs) in the frequency range of 0.4 to 0.6 THz, and the measured Q-factors of the two GMRs are as high as 334 and 152, respectively. In addition, the influence of the thickness of the silicon substrate on the two resonances is analyzed in detail. The proposed all-silicon THz metasurface has great potential in the design and application of high-Q metasurfaces.

Optical metasurfaces are two-dimensional ultrathin devices based on single-layer or multilayer arrays of subwavelength nanostructures. They can achieve precise control of phase, amplitude, and polarization on the subwavelength scale. In this paper, a substrate-free all-silicon coded grating is designed, which can realize the phase control of the outgoing beam after the y-polarized plane wave is vertically incident on the metasurface at 0.1 THz. Through a single-layer silicon nanoarray structure, a low-reflection anomalous transmission metasurface is realized, and a variety of different beam deflectors are designed based on these encoded gratings. We propose a coded grating addition principle, which adds and subtracts two traditional coded grating sequences to obtain a new coded grating sequence. The encoded supergrating can flexibly control the scattering angle, and the designed substrate-free all-silicon encoded grating can achieve a deflection angle of 48.59°. In order to verify the principle of coded grating addition, we experimented with cascade operation of two coded sequence gratings to obtain the flexible control of the terahertz beam of the composite supergrating. The principle of grating addition provides a new degree of freedom for the flexible regulation of the terahertz wavefront. At the same time, this method can be extended to the optical band or microwave band, opening up new ways for electromagnetic wave manipulation and beam scanning.

High-Q metasurfaces have important applications in high-sensitivity sensing, low-threshold lasers, and nonlinear optics due to the strong local electromagnetic field enhancements. Although ultra-high-Q resonances of bound states in the continuum (BIC) metasurfaces have been rapidly developed in the optical regime, it is still a challenging task in the terahertz band for long years because of absorption loss of dielectric materials, design, and fabrication of nanostructures, and the need for high-signal-to-noise ratio and high-resolution spectral measurements. Here, a polarization-insensitive quasi-BIC resonance with a high-Q factor of 1049 in a terahertz all-silicon metasurface is experimentally achieved, exceeding the current highest record by 3 times of magnitude. And by using this ultra-high-Q metasurface, a terahertz intensity modulation with very low optical pump power is demonstrated. The proposed all-silicon metasurface can pave the way for the research and development of high-Q terahertz metasurfaces.

The interaction between magnetic quantum emitters and the local electromagnetic environment is a promising method to manipulate the spontaneous emission. However, it is severely limited by the weak interactions between the magnetic component of light and natural materials. Herein, we demonstrate that the special type of anapole states associated with the “onefold” electric toroidal dipole moment can be excited by efficient interaction between magnetic dipole emitters and silver oligomers. Based on magnetic anapole states, the radiative power is effectively suppressed with significant coupling between the emitter and the silver nonamer, physically providing an ideal playground for the study of non-radiative transitions. These findings not only introduce magnetic anapoles to plasmonics but also open a door for the development of new high-performance magnetic-dipole-based optoelectronic devices.