In this paper, a kind of plasma metastructures-photonic crystals (PMPC) structure is proposed to investigate the absorption and transmission properties of electromagnetic waves (EWs) incident from opposite directions. The results show that the PMPC can achieve a dual-channel asymmetric absorption-transmission (AAT) phenomenon. At an operating bandwidth (OB) of 2.15∼2.85 GHz, EWs are absorbed in the forward incidence and transmitted in the backward case, and a relative bandwidth (RB) with forward absorption above 0.9 is 28.0%. On the contrary, at an OB of 7.07∼7.67 GHz, EWs can be transmitted in the forward propagation and absorbed in the backward case with a RB of 8.1%. Moreover, the effects of parameters such as applied magnetic field, incident angle, and tilt angle on AAT performance are investigated separately. The proposed dual-channel tunable AAT will further extend the application of asymmetric devices in the fields of optical communication and optical transmission.

Photonic spin Hall effect (PSHE) is an effective metrological tool to characterize the variation in weak refractive index (RI) and nanostructure parameters. In this Letter, a highly sensitive terahertz Janus sensor (JS) based on PSHE is proposed. Through the asymmetric arrangement of different dielectrics, the sensor has a Janus feature, realizing the multitasking of thickness and RI detection on multiple scales. When electromagnetic waves (EWs) are incident into the JS from the forward scale, the number of graphene layers (1–7 layers) can be exactly identified by thickness detection. Enhancing the PSHE by the property of graphene, the JS can extend the thickness change of the graphene layer at the nanometer level by 106 times to the millimeter level with a sensitivity of 3.02 × 10−3 m/nm. In the case of EWs backward scale propagation, based on the sensitivity of 6.244 × 10−3 m/RIU, the JS can identify different kinds of waterborne bacterium such as Vibrio cholerae, Escherichia coli, and Shigella flexneri, in the RI range of 1.355–1.43 with high precision. The design of the multiscale and multitasking JS with high sensitivity is of great significance for accelerating the research and exploration of graphene materials. In addition, it provides an idea for real-time, no-label, and low-cost detection in the biomedical field.

In this paper, a liquid crystal-modulated metastructure sensor (MS) is proposed that can detect the refractive index (RI) of a liquid and change the detection range under different applied voltages. The regulation of the detection range is based on the different bias states of the liquid crystal at different voltages. By changing the sample in the cavity that is to be detected, the overall electromagnetic characteristics of the device in the resonant state are modified, thus changing the position of the absorption peaks so that different RI correspond to different absorption peaks, and finally realizing the sensing detection. The refractive index unit is denoted as RIU. The range of the refractive index detection is 1.414–2.828 and 2.121–3.464, and the corresponding absorption peak variation range is 0.8485–1.028 THz and 0.7295–0.8328 THz, with a sensitivity of 123.8 GHz/RIU and 75.6 GHz/RIU, respectively. In addition, an approach to optimizing resonant absorption peaks is explored, which can suppress unwanted absorption generated during the design process by analyzing the energy distribution and directing the current flow on the substrate. Four variables that have a more obvious impact on performance are listed, and the selection and change trend of the numerical values are focused on, fully considering the errors that may be caused by manufacturing and actual use. At the same time, the incident angle and polarization angle are also included in the considered range, and the device shows good stability at these angles. Finally, the influence of the number of resonant rings on the sensing performance is also discussed, and its conclusion has guiding value for optimizing the sensing demand. This new liquid crystal-modulated MS has the advantages of a small size and high sensitivity and is expected to be used for bio-detection, sensing, and so on. All results in this work were obtained with the aid of simulations based on the finite element method.

The photonic spin Hall effect (PSHE) is an effective measurement approach to characterize changes in pressure and weak refractive index. The metastructure based on a layered structure is equipped with the Janus feature by the asymmetric arrangement of different dielectrics. Electromagnetic waves (EWs) exhibit different electromagnetic characteristics when propagate from opposite directions of the metastructure within the short-wave infrared (SWIR) range. When EWs are incident positively at a frequency $f$ of 260.87 THz ( $\lambda $ = $1.15~\mu \text{m}$ ), a Janus metastructure (JM) based on PSHE can realize wide-range pressure detection (0–17.2 GPa) with the sensitivity (S) of 1.421°/GPa by using photoelasticity relation of the dielectrics. On the negative scale (EWs incident at $f$ = 128.39 THz, that is $\lambda $ = $2.34~\mu \text{m}$ ), stomach cells, liver cells, epidermal cells, and their corresponding cancer cells can be clearly distinguished by the JM refractive index (RI) biosensing with the high resolution up to $1\times 10^{-6}$ RIU and S = $5.292\,\, {}\times {}10^{-2}$ m/RIU. The multiscale and multitasking JM proposed not only makes up for the shortcomings of traditional single-scale and single-function sensors, but more importantly, the JM provides a new idea for the development of industrial production, healthcare, and biomedical fields, due to its excellent performance and real-time, label-free and noncontact detection.