A tunable ultra-broadband and ultra-high sensitivity far-infrared metamaterial absorber based on VO2 and graphene.

We proposed a far-infrared tunable metamaterial absorber using vanadium dioxide (VO2) and graphene as controlling materials. The properties of the absorber are investigated theoretically using the finite-difference time-domain (FDTD) technique. It was found that when the Fermi energy level of graphene is fixed at zero, VO2 is in the insulated state, and the metasurface exhibits far-infrared broadband absorption performance, with absorptance exceeding 90% in the wavelength range of 12.6 µm to 23.2 µm. In addition, by elevating the Fermi energy level of graphene, the absorption bandwidth of the device is expanded continuously. When the VO2 is in the metallic state, the device can flexibly transform into a far-infrared narrowband absorber. The device also has the advantage of being insensitive to changes in polarization and incident angle. The origin of the absorption and the tuning principle of the device were analyzed and verified successfully by using an equivalent circuit model (ECM). Besides, we also studied the refraction index sensing characteristics of the absorber. Surprisingly, the absorber exhibits excellent sensing characteristics, and its sensitivity (S) reaches 14.108 µm per RIU and the figure of merit (FOM) is 6.13 per RIU.

Ultra-high Q-factor and amplitude-tunable Fano resonance in vanadium dioxide-silicon hybrid metamaterials.

As the resonance response in magnetic systems usually occurs at low frequencies, previously known as terahertz high Q-factor resonances, are mainly excited by electrical resonances. In this paper, we present a metamaterial based on vanadium dioxide-silicon arrays capable of achieving a Q-factor of up to 165 198; the ultra-high Q-factor Fano resonance excited by the proposed metamaterial is mainly affected by strong magnetic resonance. The analysis of diffractive coupling theory, electric field, magnetic field and current distribution shows that strong magnetic resonance is mainly realized by coupling localized plasmon resonance with the lattice resonance. Due to the conductivity-tunable nature of vanadium dioxide, the proposed metamaterial features an amplitude tunable function with a modulation depth of 98.8%. The spectral response of the analyte demonstrates the capability of the proposed metamaterial for application as a sensor with a maximum sensitivity of 69.52 GHz per RIU and a figure of merit of 15 456. The ultra-high Q-factor performance and amplitude tunability of the proposed structure can be applied to terahertz devices, such as ultrasensitive sensors, filters and optical switches.

A switchable and tunable multifunctional terahertz polarization converter based on a graphene metasurface.

We propose a switchable and tunable terahertz metasurface polarization converter based on graphene. The metasurface is composed of a bottom gold film, a lower SiO2 layer, an intermediate N-type graphene layer, an upper SiO2 layer, and a top layer of square graphene resonant rings. By using the CST Microwave Studio, we studied their polarization conversion properties. The results show that the metasurface enables a versatile range of functions, including x-to-y linear polarization conversion within the frequency range of 4.23-7 THz, the transformation of linearly polarized waves into right-hand circularly polarized and left-hand circularly polarized waves. Moreover, at 3.873 THz, the metasurface can exhibit circular dichroism (CD) with a high CD value of 0.7. Based on the effect, a strategy to detect three representative avian influenza viruses was proposed and tested, which implies that the metasurface can be applied in biosensing.

A Quick Method for Predicting Reflectance Spectra of Nanophotonic Devices via Artificial Neural Network.

Nanophotonics use the interaction between light and subwavelength structures to design nanophotonic devices and to show unique optical, electromagnetic, and acoustic properties that natural materials do not have. However, this usually requires considerable expertise and a lot of time-consuming electromagnetic simulations. With the continuous development of artificial intelligence, people are turning to deep learning for designing nanophotonic devices. Deep learning models can continuously fit the correlation function between the input parameters and output, using models with weights and biases that can obtain results in milliseconds to seconds. In this paper, we use finite-difference time-domain for simulations, and we obtain the reflectance spectra from 2430 different structures. Based on these reflectance spectra data, we use neural networks for training, which can quickly predict unseen structural reflectance spectra. The effectiveness of this method is verified by comparing the predicted results to the simulation results. Almost all results maintain the main trend, the MSE of 94% predictions are below 10-3, all are below 10-2, and the MAE of 97% predictions are below 2 × 10-2. This approach can speed up device design and optimization, and provides reference for scientific researchers.

Switchable and Tunable Terahertz Metamaterial Based on Vanadium Dioxide and Photosensitive Silicon.

A switchable and tunable terahertz (THz) metamaterial based on photosensitive silicon and Vanadium dioxide (VO2) was proposed. By using a finite-difference time-domain (FDTD) method, the transmission and reflective properties of the metamaterial were investigated theoretically. The results imply that the metamaterial can realize a dual electromagnetically induced transparency (EIT) or two narrow-band absorptions depending on the temperature of the VO2. Additionally, the magnitude of the EIT and two narrow-band absorptions can be tuned by varying the conductivity of photosensitive silicon (PSi) via pumping light. Correspondingly, the slow-light effect accompanying the EIT can also be adjusted.

Difunctional terahertz metasurface with switchable polarization conversion and absorption by VO2 and photosensitive silicon.

In this study, a terahertz (THz) switchable multifunctional metasurface is proposed to realize polarization conversion and absorption. When vanadium dioxide (VO2) is in the dielectric state, the structure demonstrates polarization conversion with double broadband transmission. The transmittance of the double broadband is greater than 80% in the frequency ranges of 2.05-2.38 THz and 3.38-3.68 THz, and the polarization conversion rate (PCR) is greater than 90%. Excellent asymmetric transmission (AT) properties are exhibited by polarization conversion. The transmittance of the double broadband can be modulated dynamically by the pump light by controlling the conductivity of the photosensitive silicon (PS). When VO2 is in the metallic state, the metasurface is switched to be a bidirectional THz absorber for TE and TM wave incidence, and the maximum absorptance of the absorber can reach more than 95%. Furthermore, the absorption is insensitive to the angle of incidence, and the absorption frequency and intensity can be dynamically tuned by changing the polarization angle. By changing the conductivity of the PS, the intensity and frequency of the absorption can also be adjusted. Using the metasurface, we achieved a dynamic multiplexing imaging function for linearly polarized waves. The metasurface showed a new vision for multifunctional THz devices and exhibited a wide application prospect in the field of THz imaging.

RNA sequencing reveals the mechanism of FTO in inhibiting inflammation and excessive proliferation of lipopolysaccharide-induced human glomerular mesangial cells.

Chronic glomerulonephritis (CGN) is a leading cause of end-stage renal disease in China; thus, there is an urgent need for effective therapeutic targets and strategies for CGN treatment. However, studies on CGN pathogenesis are limited. In this study, we found that the fat mass and obesity-associated protein (FTO) was significantly decreased in the lipopolysaccharide (LPS)-induced human glomerular mesangial cells (HGMCs) (P < 0.01) and kidney tissues of CGN patients (P < 0.05). Moreover, double-labeling immunofluorescence and flow cytometry assays demonstrated that the overexpression of FTO could inhibit inflammation and excessive proliferation of HGMCs. Furthermore, RNA-sequencing (RNA-seq) and real-time quantitative polymerase chain reaction (RT-qPCR) analyses revealed that FTO overexpression induced differential expression of 269 genes (absolute fold change ≥ 2 and P-value < 0.05), including 143 upregulated and 126 downregulated genes. Further functional analysis of these differentially expressed genes by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses suggested that FTO possibly mediates its inhibitory function by regulating the mammalian target of rapamycin (mTOR) signaling pathway and substance metabolism. Lastly, analysis of the PPI network and further identification of the top 10 hub genes (RPS15, RPS18, RPL18A, GNB2L1, RPL19, EEF1A1, RPS25, FAU, UBA52, and RPS6) indicated that FTO mediates its function by affecting the ribosomal proteins. Therefore, in this study, we elucidated the important role of FTO in the regulation of inflammation and excessive proliferation of HGMCs, suggesting FTO administration as a suitable therapeutic intervention for CGN.

Ultrafast and low-power multichannel all-optical switcher based on multilayer graphene.

A metal-insulator-metal waveguide structure composed of a hexagonal resonator cavity and a ring with a slit is proposed. By using the finite difference time domain method, the transmission properties of the structure were studied. It was found that three distinct plasmon-induced transparency peaks appear in the visible and near-infrared bands, and the transmissivity of the three peaks is more than 80%. By tuning the structure size, the positions of the peaks can be adjusted. Then we introduced graphene, covering the surface of the cavity. By adjusting the refraction index of the graphene using light, the position of the three transmission peaks can be changed correspondingly. Based on the effect, we designed an all-optical switcher with ultrafast optical response time (about 2 ps) and low light absorption (about 2.3%). The proposed waveguide structure provides a way for the development of visible and near-infrared filters and all-optical switchers.

High-throughput data on circular RNA reveal novel insights into chronic glomerulonephritis.

BACKGROUND: Circular RNAs (circRNAs), a unique novel type of RNA, have been widely reported to be involved in physiologic and pathologic processes in humans. However, the exact molecular pathogenesis of circRNAs in chronic glomerulonephritis (CGN) is far from clear. OBJECTIVE: This paper aims to evaluate the specific expression profile of circRNAs in renal cortex tissues from Adriamycin-induced CGN rats. METHODS: CircRNAs were screened in renal cortex tissues from 3 CGN rats and 3 control rats by using high-throughput sequencing (HTS). Then, 4 circRNAs were selected randomly for verification by quantitative real-time polymerase chain reaction (qRT-PCR). In addition, the differentially expressed (DE) circRNAs were analyzed by bioinformatics methods. RESULTS: In total, 31 significantly DE circRNAs were identified, which revealed their potential roles in CGN; in particular, we found that 4 confirmed altered circRNAs (rno-circ-RNAs 689, 3217, 1327, and 5001) might play important roles in the development of CGN. CONCLUSION: This study reveals a cluster of circRNAs that are DE in Adriamycin-induced CGN rats, which brings us closer to understanding the pathogenic mechanisms and may provide new potential targets for clinical treatment.

Ultrafast nonlinear absorption with multiple transformations and transient dynamics of gold nanobipyramids.

The process and condition of saturable absorption (SA) and reverse saturable absorption (RSA) of ultrafast nonlinear optics in metal nanoparticles are essential for applications including light generation, amplification, modulation, and switching. Here, we first discover and explore the multiple transformations (SA-RSA-SA) of ultrafast nonlinear absorption behavior of metal nanoparticles in femtosecond pulses. Correspondingly, the energy level model and fitting formula of multiple transformations are established to illustrate the process of optical response. The femtosecond transient absorption spectra provide information about their ultrafast dynamics process and vibrational mode, which further reveals the multiple transformation mechanisms of nonlinear absorption in gold nanobipyramids (Au-NBPs). Furthermore, Au-NBPs exhibit a significantly higher SA modulation depth up to 42% in the femtosecond, which is much higher than the reported values of other nanomaterials. Our results indicate that Au-NBPs can be used as broadband ultrafast Q-switching and mode-locking, and the conversion offers new opportunities for metal nanostructures in applications of optical switching.

Double transformation of the nonlinear absorption in silver nanoparticles.

The nonlinear absorption of 40 nm Ag nanoparticles (Ag NPs) was investigated using open aperture (OA) Z-scan technique at 532 nm. Experiments show that the nonlinear absorption behavior of Ag NPs is intensity dependent. Specifically, under low laser energy the Ag NPs shows saturable absorption (SA). At medium laser energy, the transformation of nonlinear absorption from SA to reverse saturable absorption (RSA) happens. While under stronger laser energy, double transformation (SA→RSA→SA) of nonlinear absorption occurs. The experimental results were analyzed theoretically using a model based on single-photon absorption and two-photon absorption saturation.

Size effect on nonlinear optical properties and ultrafast dynamics of silver nanoparticles.

Z-scan technology was used to study the nonlinear absorption (NLA) and nonlinear refraction (NLR) of silver nanoparticles (Ag NPs) with various sizes under different laser intensities. The results demonstrate that the NLA and NLR of Ag NPs were size-dependent. Specifically, the 10 nm Ag NPs exhibit saturation absorption (SA) and insignificant NLR. The 20 and 40 nm Ag NPs show the coexistence of SA and reverse saturation absorption (RSA). SA is believed to result from ground-state plasma bleaching, whereas RSA originates from excited state absorption (ESA). The 20 nm and 40 nm Ag NPs shows increasing self-defocusing with the increase of laser intensity. It was observed that the energy relaxation of Ag NPs mainly includes two processes of electron-phonon and phonon-phonon couplings on the order of picoseconds.

Dual-Channel Mid-Infrared Toroidal Metasurfaces for Wavefront Modulation and Imaging Applications.

In this paper, we propose a dual-channel mid-infrared toroidal metasurface that consists of split equilateral triangular rings. The electromagnetic responses are analyzed by the finite-difference-time-domain (FDTD) method and temporal coupled-mode theory (TCMT). The results show that one channel of the metasurface is insensitive to the polarization angle of the incident light and temperature, while the other channel is sensitive. The reflectance and resonance wavelength can be manipulated by the polarization angle and temperature independently. Based on such a mechanism, we propose metasurfaces for two-bit programmable imaging and thermal imaging. The metasurfaces are believed to have potential applications in information processing and thermal radiation manipulation.

An Infrared Ultra-Broadband Absorber Based on MIM Structure.

We designed an infrared ultra-broadband metal-insulator-metal (MIM)-based absorber which is composed of a top layer with four different chromium (Cr) nano-rings, an intermediate media of aluminum trioxide (Al2O3), and a bottom layer of tungsten (W). By using the finite-difference time-domain (FDTD), the absorption performance of the absorber was studied theoretically. The results indicate that the average absorption of the absorber can reach 94.84% in the wavelength range of 800-3000 nm. The analysis of the electric and magnetic field indicates that the ultra-broadband absorption rate results from the effect of local surface plasmon resonance (LSPR). After that, the effect of structural parameters, metal and dielectric materials on the absorptivity of the absorber was also discussed. Finally, the effect of incidence angle on absorption was investigated. It was found that it is not sensitive to incidence angle; even when incidence angle is 30°, average absorptivity can reach 90%. The absorber is easy to manufacture and simple in structure, and can be applied in infrared detection and optical imaging.

Visible and Near-Infrared Broadband Absorber Based on Ti3C2Tx MXene-Wu.

A high absorption broadband absorber based on MXene and tungsten nanospheres in visible and near-infrared bands is proposed. The absorber has a maximum absorption of 100% and an average absorption of 95% in the wavelength range of 400-2500 nm. The theoretical mechanism and parameter adjustability of the absorber are analyzed by FDTD solutions. The results show that the structural parameters can effectively adjust the absorption performance. The good absorption performance is due to the action of the local surface plasmon resonance coupling with the gap surface plasmon resonance and Fabry-Perot resonance. The simulation results show that the absorber is insensitive to the polarization and oblique incidence angle of incident light, and that high absorption and broadband can be maintained when the oblique incidence angle is up to 60°.

Switchable Terahertz Absorber from Single Broadband to Dual Broadband Based on Graphene and Vanadium Dioxide.

A multifunctional switchable terahertz (THz) absorber based on graphene and vanadium dioxide (VO2) is presented. The properties of the absorber are studied theoretically by the finite-difference time-domain (FDTD) method. The results illustrate that the structure switches between the single-broadband or double-broadband absorption depending on the temperature of VO2. Moreover, the amplitude of the absorptivity can be adjusted by changing the Fermi energy level (EF) of graphene or the conductivity of VO2 separately. Via impedance matching theory, the physical mechanism of the absorber is researched. Furthermore, the effects of incidence angle on absorption have also been studied. It is found that the absorber is insensitive to the polarization of electromagnetic waves.

Dynamic Modulation of THz Absorption Frequency, Bandwidth, and Amplitude via Strontium Titanate and Graphene.

A multi-functional broadband absorber based on graphene and strontium titanate (STO) film was designed. Additionally, the frequency, bandwidth, and amplitude of the absorber could be tuned by adjusting temperature and Fermi level of the graphene. By using the finite-difference time-domain (FDTD) method, the numerical calculation result shows that, when keeping the device temperature at 230 K and setting graphene Fermi level to be 1 eV, three absorption peaks at 1.72 THz, 2.08 THz, and 2.59 THz were realized and combined into a broadband absorption from 1.68 to 2.74 THz. As the STO temperature was increased from 230 K to 310 K, the center frequency moved from 2.2 THz to 2.45 THz; correspondingly, the broadband absorption range was widened from 1.06 THz to 1.24 THz. When the temperature was fixed at 230 K and the graphene Fermi level was tuned from 1 eV to 0.7 eV, the absorption bandwidth decreased from 1.06 THz to 0.64 THz. While the Fermi level was tuned continually to be 0.01 eV, only a single absorption peak with an absorption rate of 0.29 existed. The broadband absorption and tuning mechanism of the absorber were analyzed using impedance matching theory. Furthermore, we also studied the effect of incident angle and polarization direction on the properties of the absorber. The multi-functional tunable absorber provides potential applications for the design of more efficient terahertz functional devices in the future.

Multi-Channel High-Performance Absorber Based on SiC-Photonic Crystal Heterostructure-SiC Structure.

The multi-channel high-efficiency absorber in the mid-infrared band has broad application prospects. Here, we propose an SiC-photonic crystal (PhC) heterostructure-SiC structure to realize the absorber. The absorption characteristics of the structure are studied theoretically. The results show that the structure can achieve high-efficiency multi-channel absorption in the mid-infrared range. The absorption peaks come from the coupling of the dual Tamm phonon polariton (TPhP) mode formed at the interface between the two SiC layers and the photonic crystal, and the optical Tamm state (OTS) mode formed in the PhC heterostructure. By adjusting the thickness of the air dielectric layer and the period of the PhC in the heterostructure, the mode coupling intensity can be regulated; thereby, the position and intensity of the absorption peak can be adjusted. In addition, the absorption peaks of TE and TM polarized light can be controlled by changing the incident angle. Adjusting the incident angle can also control the excitation and intensity of the epsilon-near-zero (ENZ) phonon polariton mode produced by TM polarized light. This kind of light absorber may have potential applications in sensors, filters, modulators, switches, thermal radiators, and so on.

Dual-Spectral Plasmon-Induced Transparent Terahertz Metamaterial with Independently Tunable Amplitude and Frequency.

A bifunctional tunable metamaterial composed of pattern metal structure, graphene, and strontium titanate (STO) film is proposed and studied numerically and theoretically. The dual plasmon-induced transparency (PIT) window is obtained by coupling the bright state cut wire (CW) and two pairs of dark state dual symmetric semiring resonators (DSSRs) with different parameters. Correspondingly, slow light effect can also be realized. When shifting independently, the Fermi level of the graphene strips, the amplitudes of the two PIT transparency windows and slow light effect can be tuned, respectively. In addition, when independently tuning the temperature of the metamaterial, the frequency of the dual PIT windows and slow light effect can be tuned. The physical mechanism of the dual-PIT was analyzed theoretically by using a three-harmonic oscillator model. The results show that the regulation function of the PIT peak results from the change of the oscillation damping at the dark state DSSRs by tuning conductivity of graphene. Our design presents a new structure to realize the bifunctional optical switch and slow light.

Detection of GDF11 by using a Ti3C2-MXene-based fiber SPR biosensor.

In the research of resistant aging, the concentration of Growth differentiation factor-11(GDF11) is an indispensable parameter. So the accurate detection of GDF11 is very important in life science and medical cosmetology. Hereby, we proposed and demonstrated a simple method to detect low concentration GDF11 by using fiber surface plasmon resonance (SPR) sensor decorated with two-dimension (2D) material Ti3C2-MXene and gold nanosphere. The sensitivity of the fiber SPR sensor was increased to be 4804.64nm/RIU. After functionalized with GDF11 antibody, the fiber SPR sensor could specifically recognize GDF11, and the limit of detection (LOD) can reach 0.577pg/L which is 100 times lower than that of single-molecule ELISA method.