An optimized metastructure switchable between ultra-wideband angle-insensitive absorption and transmissive polarization conversion: a theoretical study.

An optimized metastructure (MS) switchable between ultra-wideband (UWB) angle-insensitive absorption, and transmissive linear-to-circular (LTC) polarization conversion (PC), is proposed, which is a theoretical study. The structural parameters of this MS are optimized by the thermal exchange optimization algorithm. By modulating the chemical potential (µc) of the graphene-based hyperbolic metamaterial embedded in the MS, the MS can achieve UWB absorption in the absorption state and LTC PC in the transmission state. At normal incidence, in the absorption state, the MS exhibits absorptivity exceeding 0.9 within 7-15.45 THz, with a relative bandwidth (RBW) of 75.28%. By elevating µc, an UWB LTC PC is realized, with a RBW of 118.8%, achieving transmittance above 0.9 and the axial ratio below 3 dB. When prioritizing the angular stability, in the absorption state, the MS secures the angular stability of 75° for TE waves and 65° for TM ones. In the transmission state, the angular stability of PC reaches 60°, with RBW = 100.7%. Moreover, by manipulating µc, the tunability of UWB absorption is realized. The optimized MS provides a reference for designing multifunctional intelligent terahertz modulators, with promising application potential in domains like electromagnetic shielding, communication systems, and THz modulation.

A multiple cancer cell optical biosensing metastructure realized by CPA.

A one-dimensional optical biosensing metastructure (OBM) with graphene layers is presented in this paper. It is realized by coherent perfect absorption (CPA) and operates in the transverse electric mode. It shows a strong linear fitting relationship between the refractive index (RI) of the analysis layer and the frequency corresponding to the absorption peak, and the R-square is up to 1. Additionally, based on the principle of CPA, the OBM can realize the function of multiple cancer cell detection by adjusting the detection range by controlling the phase difference of coherent electromagnetic waves. Its detection ranges are 1.34-1.355 and 1.658-1.662. Thanks to its high-quality factor, great figure of merit, and low detection limit, whose best values are, respectively, 6.9 × 104, 1.2 × 104 RIU-1, and 3.6 × 10-6 RIU, the detection of weak changes in the RI of a cancer cell is possible. Additionally, its sensitivity can reach 26.57 THz RIU-1. This OBM based on CPA has major implications for advancing the study and investigation into the application of CPA. It also provides a simple and efficient approach to distinguish cancer cells and may be widely used in the biomedical field.

A multi-physical quantity sensor based on a layered photonic structure containing layered graphene hyperbolic metamaterials.

The layered photonic structure (LPS) sensor presented in this paper utilizes the intrinsic absorption principle of graphene which can improve the absorption rate by stacking layers to generate an absorption peak within the terahertz (THz) frequency range. The absorption peak can be used for multi-dimensional detection of glucose solution, alcohol solution, the applied voltage of graphene, the thickness of hyperbolic metamaterials (HMs), and room temperature. LPS is endowed with characteristics of a Janus metastructure through the non-stacked arrangement of different media and can have different sensing properties when the electromagnetic waves (EWs) are incident forward and backward. The Janus metastructure features in the forward and backward direction make it have different physical characteristics, forming sensors with different resolutions and qualities, so as to realize the detection of multiple physical quantities. One device has the detection performance of multiple substances, which greatly improves the utilization rate of the design structure. Furthermore, the addition of HM to the sensor structure enables it to exhibit angle-insensitive characteristics in both forward and backward directions. To further enhance the sensor's performance, the particle swarm optimization (PSO) algorithm is used to optimize structural parameters. The resulting sensor exhibits excellent sensing performance, with a high sensitivity (S) of 940.34 THz per RIU and quality factor (Q) and figure of merit (FOM) values of 37 4700 RIU-1, respectively, when measuring voltage. For glucose and alcohol solutions, the sensor demonstrates S values of 5.52 THz per RIU and 4.44 THz per RIU, Q values of 8.3 and 37.2, and FOM values of 6.2 RIU-1 and 20.2 RIU-1, respectively in different directions.

Advanced optical terahertz fingerprint sensor based on coherent perfect absorption.

An advanced optical terahertz (THz) fingerprint sensor based on coherent perfect absorption (CPA) is proposed. Based on a one-dimensional layered photonic structure, the sensor contains a cavity that is developed for THz fingerprint measurement. Utilizing the magneto-optical effect of magnetized InSb, CPA is excited in the structure of the sensor. Taking α-lactose as exemplar material, this numerical simulation is integrated with a Drude-Lorentz model. The transfer matrix method (TMM) is used to calculate the sensitivity (S), linear range (LR), quality (Q), the figure of merit (FOM*), and detection limit (DL) theoretically. Employing the amplitude modulation detection method, the qualitative and quantitative analysis of the α-lactose thickness of 0-0.5 µm could be realized. Because of the fragility of CPA, the S is 0.78255 µm-1, the value of average Q is up to 8019.2, the value of average FOM* is 13 234.4 (THz µm)-1, and the lower DL is 4.21 × 10-6. Moreover, the evolutions of ensemble-averaged absorption in the vicinity of the absorption peaks for different types of disorder effects are considered, which will be considered in the fabrication of sensors.