Manipulating the light-matter interaction in a topological photonic crystal heterostructure.

We theoretically and numerically investigate the ligh-matter interaction in a classic topological photonic crystal (PhC) heterostructure, which consists of two opposite-facing 4-period PhCs spaced by a dielectric layer. Due to the excitation of topological edge mode (TEM) at the interface of the two PhCs, the strong coupling between incident light and TEM produces a high quality resonance peak, which can be applied to many optical devices. As a refractive index sensor, it achieves a sensitivity of 254.5 nm/RIU and a high figure of merit (> 250), which is superior to many previously reported sensors. We further study the coupling between photons and excitons by replacing the pure dielectric layer with the J-aggregates doped layer. By tuning the thickness of the doped layer and the angle of incident light, the dispersive TEM can efficiently interact with the molecular excitons to form a hybrid mode with TEM-like or exciton-like components, showing interesting energy transfer characteristics and flexible modulation characteristics. This work may be helpful for a better understanding of light-matter interactions in a topological PhC heterostructure, and achieve potential applications in related optical devices.

Multichannel direct transmissions of near-field information.

A digital-coding programmable metasurface (DCPM) is a type of functional system that is composed of subwavelength-scale digital coding elements with opposite phase responses. By configuring the digital coding elements, a DCPM can construct dynamic near-field image patterns in which the intensity of each pixel of the image can be dynamically and independently modulated. Thus, a DCPM can perform both spatial and temporal modulations. Here, this advantage is used to realize multichannel direct transmissions of near-field information. Three points are selected in the near-field region to form three independent channels. By applying various digital phase codes on the DCPM, independent binary digital symbols defined by amplitude codes (namely, weak and strong amplitudes) are transmitted through the three channels. The measured near-field distributions and temporal transmissions of the system agree with numerical calculations. Compared with the conventional multichannel transmission, the proposed mechanism achieves simultaneous spatial and temporal modulations by treating DCPM as an energy radiator and information modulator, thereby enduing DCPM with high potential in near-field information processing and communications.

Negative reflection and negative surface wave conversion from obliquely incident electromagnetic waves.

Complete control of spatially propagating waves (PWs) and surface waves (SWs) is an ultimate goal that scientists and engineers seek for, in which negative reflection of PW and negative surface wave are two exotic phenomena. Here, we experimentally demonstrate an anisotropic digital coding metasurface capable of controlling both PWs and SWs with a single coding pattern. On the basis of the digital description of coding metasurfaces, a simple coding method is proposed to allow dual functionalities (either PW or SW manipulations) under two orthogonal polarizations at arbitrarily oblique incidences, thus improving the adaptability of digital coding metasurfaces in more practical circumstances. With elaborately designed ellipse-shaped coding particles, we experimentally demonstrate various functions under oblique incidences, including the negative reflection of PW, negative SW, anomalous reflection and their arbitrary combinations, all having good agreements with theoretical and numerical predictions. We believe that the proposed method may enable the digital coding metasurfaces to have broad applications in radar detections, wireless communications and imaging.

Electromagnetic reprogrammable coding-metasurface holograms.

Metasurfaces have enabled a plethora of emerging functions within an ultrathin dimension, paving way towards flat and highly integrated photonic devices. Despite the rapid progress in this area, simultaneous realization of reconfigurability, high efficiency, and full control over the phase and amplitude of scattered light is posing a great challenge. Here, we try to tackle this challenge by introducing the concept of a reprogrammable hologram based on 1-bit coding metasurfaces. The state of each unit cell of the coding metasurface can be switched between '1' and '0' by electrically controlling the loaded diodes. Our proof-of-concept experiments show that multiple desired holographic images can be realized in real time with only a single coding metasurface. The proposed reprogrammable hologram may be a key in enabling future intelligent devices with reconfigurable and programmable functionalities that may lead to advances in a variety of applications such as microscopy, display, security, data storage, and information processing.Realizing metasurfaces with reconfigurability, high efficiency, and control over phase and amplitude is a challenge. Here, Li et al. introduce a reprogrammable hologram based on a 1-bit coding metasurface, where the state of each unit cell of the coding metasurface can be switched electrically.

Shaping electromagnetic waves using software-automatically-designed metasurfaces.

We present a fully digital procedure of designing reflective coding metasurfaces to shape reflected electromagnetic waves. The design procedure is completely automatic, controlled by a personal computer. In details, the macro coding units of metasurface are automatically divided into several types (e.g. two types for 1-bit coding, four types for 2-bit coding, etc.), and each type of the macro coding units is formed by discretely random arrangement of micro coding units. By combining an optimization algorithm and commercial electromagnetic software, the digital patterns of the macro coding units are optimized to possess constant phase difference for the reflected waves. The apertures of the designed reflective metasurfaces are formed by arranging the macro coding units with certain coding sequence. To experimentally verify the performance, a coding metasurface is fabricated by automatically designing two digital 1-bit unit cells, which are arranged in array to constitute a periodic coding metasurface to generate the required four-beam radiations with specific directions. Two complicated functional metasurfaces with circularly- and elliptically-shaped radiation beams are realized by automatically designing 4-bit macro coding units, showing excellent performance of the automatic designs by software. The proposed method provides a smart tool to realize various functional devices and systems automatically.

Ultralow temperature terahertz magnetic thermodynamics of perovskite-like SmFeO3 ceramic.

The terahertz magnetic properties of perovskite-like SmFeO3 ceramic are investigated over a broad temperature range, especially at ultralow temperatures, using terahertz time-domain spectroscopy. It is shown that both resonant frequencies of quasi-ferromagnetic and quasi-antiferromagnetic modes have blue shifts with the decreasing temperature due to the enhancement of effective magnetic field. The temperature-dependent magnetic anisotropy constants are further estimated using the resonant frequencies, under the approximation of omitting the contribution of Sm(3+) magnetic moments to the effective field. Specially, the effective anisotropy constants in the ca and cb planes at 3 K are 6.63 × 10(5) erg/g and 8.48 × 10(5) erg/g, respectively. This thoroughly reveals the terahertz magnetic thermodynamics of orthoferrites and will be beneficial to the application in terahertz magnetism.