Electromagnetically Induced Transparency Research Articles

Qualitative and Quantitative Recognition of Volatile Organic Compounds in Their Liquid Phase Based on Terahertz Microfluidic EIT Meta-Sensors

Volatile organic compounds (VOCs) are directly associated with human health concerns and environment safety. Therefore, it is urgent to achieve an accurate detection of VOCs both qualitatively and quantitatively. In this work, the qualitative detection of ethyl benzene (EB), isopropyl alcohol (IPA), ethyl acetate (EA) – three pure VOCs in liquid phase were discussed using terahertz (THz) microfluidic Electromagnetic Induced Transparency (EIT) meta-sensor. The THz response illustrated that with an increase in VOCs’ volumes (1~6μL), resonant frequencies of dual transmission dips (0.855, 1.724 THz) and the EIT peak (1.213THz) exhibited red shift. The limit of detections for pure IPA, EA, EB can achieve 5.45μg, 13.46μg, 4.35μg, respectively. The multivariate fusion (MF) model based on the EIT responses to VOCs was utilized to improve the accuracy of trace detection and classification of VOCs. Furthermore, the above method combined with principal component analysis with Gaussian mixture model (PCA-GMM) and the neural network classification algorithm support vector machine (SVM) was applied to the recognition of VOCs. In addition, the THz method is not feasible to detect trace amounts of VOCs (typically 0.3mg/L) in waste water because water is highly absorbable in THz band and VOCs will evaporate if water is removed. Here, IPA, EA, EB in soil were detected and classified by PCA-GMM combined with MF. Our results provide a new terahertz meta-sensor platform to trace detection of VOCs in liquid phase and in soil and may be used to identify hazardous wastes in illegal dumping.

Polarization angle tailored multitasking metasturcure: electromagnetically induced transparency, electromagnetically induced absorption, linear-to-circular polarization conversion

In this work, simultaneous implementation of electromagnetically induced transparency (EIT), electromagnetic induced absorption (EIA), and linear-to-circular polarization conversion (LTCPC) in the terahertz band is proposed in a metasturcture (MS) associated with tailoring the polarization angle (θ). The linear polarization (LP) waves with different θ can trigger different phenomena. EIT can be achieved with the incidence of transverse electric (TE) waves (θ = 0°), transverse magnetic (TM) waves (θ = 90°) cause the appearance of EIA, while a LP wave with θ = 45° induces the appearance of the LTCPC phenomenon. For TE waves, the EIT transparent window accompanied by the slow light effect has emerged from 0.288 to 0.797 THz, where the maximum group delay has arrived at 2.51 ps. For TM waves, an absorption peak of EIA is observed at 0.497 THz. The LTCPC phenomenon is well obtained with θ = 45° at 0.399 and 0.634 THz, where the transmission coefficient highly reaches 0.571 and 0.650. The optimal axis ratios (ARs) of LTCPC are 2.08 dB at 0.389 THz and 2.18 dB at 0.634 THz, respectively. Noteworthy, the two-oscillator and circuit models are adopted for the theoretical analysis of the EIT and EIA, and the conclusions obtained are in general agreement with the simulation results.

Analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency with high sensitivity based on simple circular ring resonators and vanadium dioxide film

An analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency (EIT) effect is proposed based on simple combination of circular ring resonators and vanadium dioxide film. The EIT-like effect is generated by bright-bright coupling resulting from adjacent ring resonators. High sensitivity up to 1.60 THz/RIU to the environmental refractive index is achieved utilizing the transparency peak. Accompanying with the EIT-like effect, the multi-band slow light phenomenon is obtained around the transparency windows. In addition, by inducing the insulator-metallic transition of the vanadium dioxide layer, the EIT-like curves can be actively manipulated while the multiple modulation is realized without refabricating the structure. Particularly, due to structural symmetry, the EIT-like windows keep unchanged and maintain noticeable with various polarization angles. The proposed structure has potential applications such as terahertz sensors, slow-light devices and modulators.

Manipulation of single stored-photon with microwave field based on Rydberg polariton.

We demonstrate a coherent microwave manipulation of a single optical photon based on a single Rydberg excitation in an atomic ensemble. Due to the strong nonlinearities in a Rydberg blockade region, a single photon can be stored in the formation of Rydberg polariton using electromagnetically induced transparency (EIT). The manipulation of the stored single photon is performed by applying a microwave field that resonantly couples the nS1/2 and nP3/2, while the coherent readout is performed by mapping the excitation into a single photon. We achieve a single photon source with g(2)(0) = 0.29 ± 0.08 at 80S1/2 without applying microwave fields. By implementing the microwave field during the storage time and retrieval process, we show the Rabi oscillation and modulation of stored photons that can be controlled to retrieve early or late. Rapid modulation frequencies up to 50 MHz can be obtained. Our experimental observations can be well explained via numerical simulations based on an improved superatom model accounting for the dipole-dipole interactions in a Rydberg EIT medium. Our work provides a way to manipulate the stored photons by employing the microwave field, which is significant for developing quantum technologies.

Quantum criticality induced strong coupling between resonant modes

We propose a scheme to achieve a strong interaction between an optical cavity and a single polariton mode of an optomechanical cavity, despite a weak initial coupling between the two. This interaction is made possible by quantum criticality, and the coupled system comprising two optical cavities and an optomechanical cavity displays a phenomenon similar to the concepts of electromagnetically induced transparency (EIT) and Autler–Townes splitting in atomic physics.

Exploring the Application of Multi-Resonant Bands Terahertz Metamaterials in the Field of Carbohydrate Films Sensing

Terahertz spectroscopy is a powerful tool for investigating the properties and states of biological matter. Here, a systematic investigation of the interaction of THz wave with “bright mode” resonators and “dark mode” resonators has been conducted, and a simple general principle of obtaining multiple resonant bands has been developed. By manipulating the number and positions of bright mode and dark mode resonant elements in metamaterials, we realized multi-resonant bands terahertz metamaterial structures with three electromagnetic-induced transparency in four-frequency bands. Different carbohydrates in the state of dried films were selected for detection, and the results showed that the multi-resonant bands metamaterial have high response sensitivity at the resonance frequency similar to the characteristic frequency of the biomolecule. Furthermore, by increasing the biomolecule mass in a specific frequency band, the frequency shift in glucose was found to be larger than that of maltose. The frequency shift in glucose in the fourth frequency band is larger than that of the second band, whereas maltose exhibits an opposing trend, thus enabling recognition of maltose and glucose. Our findings provide new insights into the design of functional multi-resonant bands metamaterials, as well as new strategies for developing multi-band metamaterial biosensing devices.

A terahertz metamaterial sensor with high-sensitivity based on electromagnetically induced transparency effect

In this study, we design an electromagnetically induced transparency (EIT) effect based on a metamaterial sensor composed of three split-ring structures in the terahertz range. The EIT transparency window appears at 1.83 THz due to the electromagnetic coupling between the three split-rings. To analyze its physical mechanism, we use the ‘two-particle’ model and obtain good consistency between the simulation and theoretical results. The simulation results also show that when the thickness of the measured object is 15 μm and the refractive index is between 1 and 1.5, the refractive index sensitivity of the sensor is as high as 423.9 GHz RIU−1, and the figure of merit value is 6.9. In addition, the sensor is used to simulate the detection and distinction of different types of microbiota. We expect that this work will pave the way for designing high-sensitivity EIT sensors in the terahertz region and promote the development of terahertz sensing and label-free detection of pathogens.

Mid‐Infrared Off‐Axis Resonant Mode Hybridization in Amorphous Silicon Sub‐Wavelength Grating Structures

AbstractIn this study, the off‐axis excited guided‐mode resonance (GMR) hybridization is experimentally investigated in one dimensional (1D) partially etched amorphous silicon (a‐Si) subwavelength grating structures operating in the mid‐infrared wavelength range. The 1D dielectric photonic lattice is a promising platform for studying resonance hybridization effects owing to its simple working principle and ease of electromagnetic design, fabrication, and experimental characterization. It is observed that with increasing duty‐cycle of the gratings, the avoided crossing between the coupled GMR branches underwent band‐closure and subsequent band‐flip, resulting in the Friedrich–Wintgen type bound‐states‐in‐the‐continuum (FW‐BICs) transitioning from the upper to the lower GMR branch. On either side of the band closure, the transmission spectra show an interesting electromagnetically induced transparency (EIT)‐like resonance, which manifests as a transmission peak within a broad transmission dip with increased electric field concentration near the peak. As a conceptual application of coupled GMRs, differential enhancement of infrared absorption from a polymethyl methacrylate (PMMA) layer coated on the grating structure with one of the optical resonances aligned to the absorption feature and the other acting as a built‐in reference is demonstrated. The differential transmission contrast is enhanced by more than two orders of magnitude when compared to that of the native PMMA layer.

Interconversion between dual-peak electromagnetically induced transparency and dual-peak electromagnetically induced absorption utilizing metasurface

Utilizing metasurface (MS), the transition between dual-peak electromagnetically induced transparency (EIT) and dual-peak electromagnetically induced absorption (EIA) in four states has been proposed in the terahertz (THz) band with the incidence of a circularly polarized (CP) wave. Additionally, the phase-change material vanadium dioxide (VO2) and photosensitive material silicon (Si) have been adopted. The four state transitions can be achieved by adjusting the pump light and the temperature which is not affected by incident CP waves. With the incidence of the pump light, Si can transform from the insulating state to the metallic state. Similarly, when the temperature exceeds 68 °C, VO2 enters the metallic state. Two different dual-peak EIT (State 1 and State 2) accompanied by slow light effect can be observed by modulating the state of VO2 without the action of Si. However, once Si is in metallic state, two different states of dual-peak EIA (State 3 and State 4) are achieved by changing the state of VO2. Notably, the MS has the property of polarization insensitivity. The theoretical oscillator model and equivalent RLC-circuit model verify the feasibility of dual-peak EIT and EIA.

Enhanced microwave metrology using an optical grating in Rydberg atoms.

An enhanced measurement of the microwave (MW) electric (E) field is proposed using an optical grating in Rydberg atoms. Electromagnetically induced transparency (EIT) of Rydberg atoms appears driven by a probe field and a control field. The EIT transmission spectrum is modulated by an optical grating. When a MW field drives the Rydberg transition, the central principal maximum of the grating spectrum splits. It is interesting to find that the magnitude of the sharp grating spectrum changes linearly with the MW E-field strength, which can be used to measure the MW E-field. The simulation result shows that the minimum detectable E-field strength is nearly 1/8 of that without gratings, and its measurement accuracy could be enhanced by about 60 times. Other discussion of MW metrology based on a grating spectrum is also presented.

Dynamic light storage based on controllable electromagnetically induced transparency effect

We analytically and numerically investigate a signal light storing mechanism based on the controllable electromagnetically induced transparency (EIT) effect. We demonstrate that the isolation between the waveguide and the cavities cannot be achieved instantly as soon as the two cavities are tuned into resonance, no matter the index tuning rate is ultrafast or slow. We also investigate the temporal evolution features of the intracavity energy when the pulse during time is prolonged. We find many periodical oscillations of the trapped energy in both cavities, and they are entirely complementary. Our analysis shows that the adiabatic wavelength conversion in both cavities and a phase difference π between them play critical roles in this phenomenon.

Application of circuit analog optimization method in fast optimization of dynamically tunable terahertz metamaterial sensor

The simulation design of terahertz metamaterial sensors with dynamically tunable parameters typically relies on manual parameter tuning for structural optimization. However, this method is often prone to subjective factors and suffer from issues such as frequent reconstruction of simulations, high computational costs, long processing times, and suboptimal optimization results. In this paper, we propose a circuit analog optimization method (CAOM), which constructs equivalent RLC parameters to achieve a highly fitted terahertz transmission spectrum frequency obtained from CST full-wave numerical simulation. To validate the effectiveness of the proposed model, we use a typical periodic structure unit, a double-nested split ring resonator (DSRR) terahertz metamaterial sensor, as the simulation object. Both the inner and outer open resonant rings of the sensor are made of graphene, as a result, the opening size and Fermi level of the resonant rings are dynamically tunable. The results of the validation demonstrate that the adjustments of the sensor parameters can be effectively mapped by the changes of the equivalent RLC parameters. And the proposed equivalent circuit model has parameter substitutability in the simulation modeling of split ring resonator type sensors. The proposed equivalent circuit model exhibits parameter substitution in the simulation modeling of open resonant ring-type sensors. To achieve optimal sensing performance for the electromagnetically induced transparency (EIT)-like resonant peak (with a resonant frequency of f 2) of the sensor under constrained conditions, we introduce the genetic algorithm (GA) into the equivalent circuit model to enable fast optimization of the opening sizes of the inner and outer resonant rings, as well as the Fermi level of the sensor. Moreover, the accuracy of the optimization results is verified by CST simulations. Finally, the optimization results show that the optimal FOM of the EIT-like resonant peak within the given parameter range is 0.712, which is greater than that of any randomly combined parameters. This numerical result demonstrates the effectiveness of the proposed CAOM. The proposed model and optimization method have potentials to inspire further research in device design, performance optimization, theoretical modeling, etc.

Variational-based approach to investigate Fano resonant plasmonic metasurfaces.

Considering the widespread applications of resonant phenomena in metasurfaces to bend, slow, concentrate, guide and manipulate lights, it is important to gain deep analytical insight into different types of resonances. Fano resonance and its special case electromagnetically induced transparency (EIT) which are realized in coupled resonators, have been the subject of many studies due to their high-quality factor and strong field confinement. In this paper, an efficient approach based on Floquet modal expansion is presented to accurately predict the electromagnetic response of two-dimensional/one-dimensional Fano resonant plasmonic metasurfaces. Unlike the previously reported methods, this method is valid over a wide frequency range for different types of coupled resonators and can be applied to practical structures where the array is placed on one or more dielectric layers. Given that the formulation is written in a comprehensive and flexible way, both metal-based and graphene-based plasmonic metasurfaces under normal/oblique incident waves are investigated, and it is demonstrated that this method can be posed as an accurate tool for the design of diverse practical tunable/untunable metasurfaces.

Multidimensional optical solitons and their manipulation in a cold atomic gas with a parity-time-symmetric optical Bessel potential

We propose a scheme to realize an optical Bessel potential with parity-time ($\mathcal{P}T$) symmetry and investigate the existence, propagation, and manipulation of multidimensional optical solitons through the interplay among diffraction, Kerr nonlinearity, and potential confinement in a cold atomic gas under the condition of electromagnetically induced transparency (EIT). We show that the system supports not only two-dimensional stationary optical solitons but also rotary ones; the stability of such solitons can be actively controlled by the gain-loss component (imaginary part), while the rotary motions can be tuned by the refractive-index component (real part) of the $\mathcal{P}T$-symmetric potential. Moreover, we demonstrate that the system allows the existence of stable three-dimensional spatiotemporal optical solitons, i.e., optical bullets, which have ultraslow propagation velocity and display helicoidal motions with controllable propagation trajectories. Due to the Kerr nonlinearity enhanced by the EIT effect, extremely low power is needed to create these multidimensional optical solitons. The results reported here are useful not only for the generation and manipulation of high-dimensional solitons via $\mathcal{P}T$-symmetric potentials, but also for promising applications in optical information processing and transmission.

Thermally controllable electromagnetically induced transparency in a coupled terahertz metamaterial

We investigate the thermally controllable electromagnetically induced transparency (EIT) effect in a planar terahertz (THz) metamaterial configuration comprising metallic semi-circular split ring resonators (MSCSRR) integrated with indium antimonide (InSb). In transmission configuration, a transparency window is observed by placing a horizontal cut wire (HCW) in close proximity to the MSCSRR. It develops by frequency detuning and strong near-field coupling between both the bright resonators. The transparency window is found to be controllable with temperature along with the structural parameters of the unit cell. The blue shift of 0.028 THz is observed when the temperature increases from 260 K to 320 K. Moreover, the group delay of the designed EIT structure can also dynamically tune by varying temperature of InSb. The shift from 3.19 ps to 1.98 ps is observed when the temperature increases from 260 K to 320 K. We used a coupled harmonic oscillator model to thoroughly understand the coupling between resonators and interpret the transparency effect. Our findings can be closely predicted from the model. The present study can be significant for the development of active and controllable terahertz photonic components such as slow light systems, buffers, etc.

Switching of electromagnetically induced transparency and absorption of graphene metastructure with the three resonators

A graphene metastructure (GMST) with switching features from electromagnetically induced transparency (EIT) and absorption (EIA) is theoretically proposed in a three-resonator system by controlling the Fermi energy (Ef) of the graphene in the terahertz (THz) regime. When Ef = 0.9 eV, the graphene has less influence on the lower EIT metastructure, and the EIT phenomenon of the three-resonator metastructure is realized. The EIT transmission window appears between 0.763 and 0.965 THz, and at 0.803 THz, the transmission peak reaches 0.860. When Ef = 0.12 eV, graphene is weakly coupled to the substructure, thus constructive interference between the three resonators generates a magnetic dipole that strongly traps the incident magnetic energy, thus contributing to the EIA phenomenon. The absorption window appears between 0.650 and 0.902 THz. The frequency point of the absorption peak of the EIA phenomenon at this time coincides perfectly with the frequency point of the transmission peak of EIT at Ef = 0.9 eV, both at 0.803 THz. The working principle of this GMST is explained through the surface current distribution. To reproduce EIT and EIA, the two oscillator model is used and the simulation results are proved to be consistent and valid. The structural parameters are also discussed and the properties of the GMST are explored.

Electromagnetically induced transparency-like effect in a lithium niobate resonator via electronic control

In this study, we theoretically proposed a method to achieve an electromagnetically induced transparency (EIT)-like effect in a whispering gallery mode resonator (WGMR) and experimentally validated the method in a lithium niobate (LN) device. Benefitting from the electro-optic and inverse piezoelectric effects of the LN material, two modes of the LN WGMR that are close in frequency can be tuned at different tuning rates, resulting in EIT-like resonance lineshapes. By varying the electric field applied to the LN WGMR, the full dynamic of the EIT-like phenomenon can be precisely controlled. The experimental results agreed well with the calculations based on the coupled mode theory. Moreover, we observed a hysteresis resulting from the photorefractive effect of LN. We believe our proposed method and demonstrated devices offer a way to control an EIT-like effect, which could have potential applications in light storage, quantum information processing, and enhanced sensing techniques.

Switchable Dual-Functional Metasurface for THz Absorption and Electromagnetically Induced Transparency

The metasurfaces based on nanostructure film play an important role in many fields. Usually, the properties and functions of metasurfaces are limited by their structure. Once the metasurface samples are processed, their functions have already been restricted. The dual-function device designed in this work utilizes the phase transition characteristic of vanadium dioxide (VO2). The entire layer of VO2 film is inserted between the double metal micro-nano structure. When VO2 film is in the metallic state after phase change, an isotropic narrow absorber is obtained in the terahertz (THz) region, which consists of a top Z-shaped meta-atom, a middle dielectric layer, and a bottom VO2 film. By adjusting structure parameters of VO2 film, perfect absorption is realized at the frequency of 0.525 THz with the overall absorption beyond 91%. When VO2 is in insulating state, the top Z-shaped meta-atom will interact with the bottom Z-shaped structure, and the resonance coupling leads to the appearance of electromagnetically induced transparency (EIT). The designed metal-VO2 hybrid metamaterial opens possible avenues for switchable functionalities in a single device.

Fano Resonance in Near-Field Thermal Radiation of Two-Dimensional Van der Waals Heterostructures.

Two-dimensional (2D) materials and their vertically stacked heterostructures have attracted much attention due to their novel optical properties and strong light-matter interactions in the infrared. Here, we present a theoretical study of the near-field thermal radiation of 2D vdW heterostructures vertically stacked of graphene and monolayer polar material (2D hBN as an example). An asymmetric Fano line shape is observed in its near-field thermal radiation spectrum, which is attributed to the interference between the narrowband discrete state (the phonon polaritons in 2D hBN) and a broadband continuum state (the plasmons in graphene), as verified by the coupled oscillator model. In addition, we show that 2D van der Waals heterostructures can achieve nearly the same high radiative heat flux as graphene but with markedly different spectral distributions, especially at high chemical potentials. By tuning the chemical potential of graphene, we can actively control the radiative heat flux of 2D van der Waals heterostructures and manipulate the radiative spectrum, such as the transition from Fano resonance to electromagnetic-induced transparency (EIT). Our results reveal the rich physics and demonstrate the potential of 2D vdW heterostructures for applications in nanoscale thermal management and energy conversion.

Two-color unidirectional reflections by modulating the spatial susceptibility in a homogeneous atomic medium.

Non-reciprocal reflections of optical signals are unusual yet fascinating to achieve the imminent applications of non-reciprocal photonic devices and circuits. The complete non-reciprocal reflection (unidirectional reflection) was recently found to be achievable in a homogeneous medium, if the real and imaginary parts of the probe susceptibility satisfy the spatial Kramers-Kronig (KK) relation. We propose a coherent four-level tripod model for realizing dynamically tunable two-color non-reciprocal reflections by applying two control fields with linearly modulated intensities. We found that, the unidirectional reflection can be obtained if the non-reciprocal frequency regions are located in the electromagnetically induced transparency (EIT) windows. This mechanism is to break the spatial symmetry by the spatial modulation of susceptibility to induce unidirectional reflections, the real and imaginary parts of the probe susceptibility are no longer required to satisfy the spatial KK relation.