Transparency-like Effect Research Articles

Tunable collective electromagnetic induced transparency-like effect due to coupling of dual-band bound states in the continuum

Tunable collective electromagnetic induced transparency-like effect due to coupling of dual-band bound states in the continuum

Dual-band terahertz metamaterials with electromagnetically induced transparency-like enabling high-performance sensing

In this paper, a high-performance metamaterial sensor with a square split-ring resonator and a double circular split-ring resonator is proposed, which can simultaneously excite broad-band and narrow-band electromagnetically induced transparency-like (EIT-like) effects in the terahertz band. First, the mechanisms of the dual-band EIT-like effects have been revealed by the analyses of the transmission spectra and surface current distributions in the metamaterial. Then, the influences of structural parameters on the dual-band EIT-like are discussed further. Finally, the metamaterial is very sensitive to the change of the refractive index of the surrounding media, and the sensitivity of the dual-band EIT-like resonances can reach 150 GHz/RIU and 237.5 GHz/RIU and the quality factor values are 1.67 and 7.92, respectively. The proposed metamaterial broadens the pathway for the excitation of multi-band EIT-like effects and offers promising applications in multi-frequency sensors, filters and many other aspects.

Polarization conversion filter based on electromagnetically induced transparency-like effect

Owing to the large losses in the conversion process of traditional polarization converters, there is an increasing demand for metasurfaces with excellent transmission performance. In this work, an efficient polarization conversion metasurface is proposed based on electromagnetically induced transparency-like (EIT-like) effect in the terahertz band. The multi-level bright mode paths are excited by an asymmetric structure to obtain orthogonal circular polarization conversion windows. The transmission window is generated by the mutual interference of two sets of bright modes with similar resonant frequencies. Then an asymmetric structure is constructed to achieve transmission window shift under TE polarization and TM polarization, thereby realizing dual-frequency polarization conversion. The metamaterial unit structure consists of four open metal resonant rings and four metal resonant strips. The working mechanism is explored by analyzing the surface current distribution, frequency response, and incident angle characteristics. The results show that electromagnetically induced transparency can be achieved under different polarizations. Furthermore, based on the EIT resonance between the two incident polarizations, the conversion from linear polarization to right-hand circular polarization is achieved at 0.692 THz, and the conversion from linear polarization to left-hand circular polarization is realized at 0.782 THz, transmission coefficients are 0.7 and 0.68 respectively. According to the Stokes parameters, the corresponding ellipticity <i>η</i> values are 96% and 98%, respectively. This EIT-based polarization conversion metasurface with low loss and ultra-thin characteristics has great potential applications in compact antennas, derived radar phased arrays, and military detectors.

Simultaneous measurement of relative humidity and temperature using EIT-like effect in photonic crystal cavity coupled system integrated with PVA and graphene

In this work, we propose a sensor based on a photonic crystal nanobeam cavity (PCNC) coupled system integrated with Polyvinyl alcohol (PVA) and graphene, which uses an electromagnetically induced transparency-like (EIT-like) effect for the simultaneous measurement of relative humidity (RH) and temperature (T). The structure consists of a bus waveguide and two types of one-dimensional PCNC supporting the dielectric and air mode resonance, respectively. The RH-sensitive material PVA is used in the dielectric mode cavity to increase the RH sensitivity and anti-interference ability. We demonstrate that the EIT-like transparency window can be actively and flexibly modulated by adjusting the Fermi level of graphene. In addition, the ability of the system to simultaneously detect RH and T is proved by using the three-dimensional finite-difference time-domain (3D-FDTD) method and the sensor matrix. The RH sensitives for the dielectric and air modes are −542.0 pm/%RH and −258.2 pm/%RH, respectively. The T sensitives for the dielectric and air modes are −14.6 pm/K and 35.4 pm/K, respectively. The sensor achieves a strong anti-interference ability and its footprint is only 12 μm × 2.02 μm. Therefore, our proposed sensor has potential applications in food storage, preservation of museum collections, human health, and biological and chemical experiments.

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.

Unidirectional Electromagnetically Induced Transparency-Like Effect with Electrically Switchable Excitation Port

Unidirectional Electromagnetically Induced Transparency-Like Effect with Electrically Switchable Excitation Port

Tunable Electromagnetically Induced Transparent Window of Terahertz Metamaterials and Its Sensing Performance

The electromagnetically induced transparency effect of terahertz metamaterials exhibits excellent modulation and sensing properties, and it is critical to investigate the modulation effect of the transparent window by optimizing structural parameters. In this work, a unilateral symmetrical metamaterial structure based on the cut-wire resonator and the U-shaped split ring resonator is demonstrated to achieve electromagnetically induced transparency-like (EIT-like) effect. Based on the symmetrical structure, by changing the structural parameters of the split ring, an asymmetric structure metamaterial is also studied to obtain better tuning and sensing characteristics. The parameters for controlling the transparent window of the metamaterial are investigated in both passive and active modulation modes. In addition, the metamaterial structure based on the cut-wire resonator, unilateral symmetric and asymmetric configurations are investigated for high performance refractive index sensing purposes, and it is found that the first two metamaterial structures can achieve sensitivity responses of 63.6 GHz/RIU and 84.4 GHz/RIU, respectively, while the asymmetric metamaterial is up to 102.3 GHz/RIU. The high sensitivity frequency response of the proposed metamaterial structures makes them good candidates for various chemical and biomedical sensing applications.

Switchable Multifunctional Terahertz Metamaterials Based on the Phase-Transition Properties of Vanadium Dioxide.

Currently, terahertz metamaterials are studied in many fields, but it is a major challenge for a metamaterial structure to perform multiple functions. This paper proposes and studies a switchable multifunctional multilayer terahertz metamaterial. Using the phase-transition properties of vanadium dioxide (VO2), metamaterials can be controlled to switch transmission and reflection. Transmissive metamaterials can produce an electromagnetically induced transparency-like (EIT-like) effect that can be turned on or off according to different polarization angles. The reflective metamaterial is divided into I-side and II-side by the middle continuous VO2 layer. The I-side metamaterials can realize linear-to-circular polarization conversion from 0.444 to 0.751 THz when the incident angle of the y-polarized wave is less than 30°. The II-side metamaterials can realize linear-to-linear polarization conversion from 0.668 to 0.942 THz when the incident angle of the y-polarized wave is less than 25°. Various functions can be switched freely by changing the conductivity of VO2 and the incident surface. This enables metamaterials to be used as highly sensitive sensors, optical switches, and polarization converters, which provides a new strategy for the design of composite functional metamaterials.

High anti-interference dual-parameter sensor using an EIT-like effect photonic crystal cavity coupled system.

We propose a sensor with high anti-interference ability using a photonic crystal cavity coupled system for simultaneous sensing of the refractive index (RI) and temperature (T) based on an electromagnetically induced transparency-like effect. A transparent window is achieved in the transmission spectrum through destructive interference between the air mode resonance and dielectric mode resonance in two one-dimensional photonic crystal structures. The T-sensitive material (SU-8) is used in the coupled system, promoting sensitivity and anti-interference ability. The capability of the system to simultaneously detect a small range of RI and T is demonstrated using three-dimensional finite-difference time-domain simulations and the fitting process. The RI sensitivities for the air and dielectric modes were 215 nm/refractive index unit (RIU) and 0 nm/RIU, respectively. The T sensitivities for the air and dielectric modes were 19 pm/K and -83pm/K, respectively. The sensor resists external interference, enabling it to resist the error caused by readings. The footprint of the sensor is 29×1.8µm2 (length×width), contributing to future optical on-chip integration sensor design.

Group delay controls of the photons transmitting through two cavities coupled by an artificial atomic ensemble: controllable electromagnetically induced transparency-like effects.

As one of the typical quantum coherence phenomena, electromagnetically induced transparency (EIT) has been extensively applied to implement various quantum coherent manipulations, typically, e.g., optical quantum memories, photonic switches, and optical quantum computations, etc. By applying the input-output theory to the photonic transports through two cavities dispersively coupled by an artificial two-level atomic ensemble, we show here that the EIT-like effects could be observed. Particularly, the transparency windows and phase shift spectra of the transmitting photons could be engineered by manipulating the atomic levels in the ensemble to adjust the effective coupling strength between the cavities. As a consequence, the group delays of the transmitting photons can be manipulated by using the EIT-like effects. The proposal is demonstrated specifically with the experimental superconducting coplanar waveguide resonators coupled by the voltage-biased electrons on liquid Helium.

Internally-tuning whispering-gallery modes in a high-Q conical microresonator for electromagnetically induced transparency-like effect

In this study, we experimentally and theoretically demonstrate electromagnetically induced transparency (EIT)-like in a single conical microresonator (CMR) fabricated by combining arc discharge and pull method. Benefited from the gradually changing diameter along the longitudinal axis of the CMR, the resonance frequency can be tuned when the CMR coupled by a tapered fiber waveguide. The characteristic of internally-tuning in our CMR is confirmed theoretically, numerically and experimentally. In particular, Fano and EIT-like effect with a quality (Q) factor are achieved by scanning the varied diameter carefully originating from approximate two resonant frequencies in a wavelength apart. In addition, these experimental observations can be well fitted with the coupled mode theory. These findings may open new avenues for realizing high-Q EIT, which pave the way for an enhanced approach in bio-sensing applications, nonlinear optics and optical switching devices.

Dynamically Tunable Electromagnetically Induced Transparency-Like Effect in Terahertz Metamaterial Based on Graphene Cross Structures

A simple and multi-layer metamaterial made of graphene to realize excellent manipulation of EIT-like effect is proposed. The unit cell consists of four layers: Substrate 1, Cross 1, Substrate 2 and Cross 2, which can obtain tunable EIT-like effect by adjusting the Fermi level of graphene. The surface current distributions of four different views clearly explain the underlying physical mechanism. A three-level Λ-type system is employed to describe the coupling process between Cross 1 and 2. The calculated transmission spectra based on two-particle model have great agreement with the simulated transmission spectra. In addition, the effects of geometrical parameters on EIT-like effect are discussed and wideband EIT-like effect with high transmission can be obtained by adjusting the lengths of Cross 1 and 2. Also, the polarization-insensitive character of EIT-like metamaterial is confirmed by the transmission spectra under different polarization angles. The maximum of group delay (25.48 ps) is far greater than the group delay of previously reported EIT-like metamaterials. Our study provides a novel way for the development of slow-light devices and modulators.

Flexibly designed polarization-independent electromagnetically induced transparency-like effect via hybrid metal–dielectric terahertz metamaterial

Opening the terahertz electromagnetic band to a wealth of applications still requires the development of new devices. For example, effective means to filter, modulate, and route terahertz beams are still required for terahertz communications, spectroscopy, and sensing to achieve their promise. In particular, metasurfaces are widely discussed for future 6G wireless communications systems. These applications, however, will also require new functionality, such as the ability to design structures enabling a more complex spectral response. Here we outline systematic design principles to realize the polarization-independent electromagnetically induced transparency-like effect in a class of planar terahertz metamaterials that can be fabricated using commonly available processes and whose structural parameters can be flexibly varied to provide wide tuning of the transparency windows within the broader absorption band. We also show how the basic concept can be used to achieve dual transparency bands.

Electromagnetically induced transparency-like effect achieved by a simple nanosystem for double modulated mode sensor

Electromagnetically induced transparency-like (EIT-like) effect is a very promising research area for ultra-sensitive sensing. Most sensors are either wavelength modulated or intensity modulated. In this paper, we propose a nanosystem, in which an EIT-like effect is generated for plasmonic sensors with integrated wavelength-modulated and intensity-modulated functions. The nanosystem consists of a gold (Au) grating andthree-layer insulator–metal–insulator structure. An EIT-like effect is formed by the destructive interference of surface plasmon polaritons (SPPs) on the upper and lower interfaces of the metallic layer. Using a two-oscillator coupling theory, we theoretically analyze the EIT-like effect and quantitatively reveal the damping characteristic of the two SPP modes and how they couple to each other. The presented nanosystem enriches the EIT-like implementation effect in plasmonic sensors.

Electromagnetically Induced Transparency-Like Effect by Dark-Dark Mode Coupling.

Electromagnetically induced transparency-like (EIT-like) effect is a promising research area for applications of slow light, sensing and metamaterials. The EIT-like effect is generally formed by the destructive interference of bright-dark mode coupling and bright-bright mode coupling. There are seldom reports about EIT-like effect realized by the coupling of two dark modes. In this paper, we numerically and theoretically demonstrated that the EIT-like effect is achieved through dark-dark mode coupling of two waveguide resonances in a compound nanosystem with metal grating and multilayer structure. If we introduce , and to represent the surface plasmon polaritons (SPPs) resonance, waveguide resonance in layer 2, and waveguide resonance in layer 4, the destructive interference occurs between two pathways of and , where is the ground state without excitation. Our work will stimulate more studies on EIT-like effect with dark-dark mode coupling in other systems.

A Metamaterial Design Based on Electromagnetic Induction Transparency-Like Effect and Its Slow-Wave Performance

This paper proposes a new metamaterial design that can achieve electromagnetic induction transparency-like (EIT-like) effects in the microwave band. The unit structure of metamaterials consists of square rings and metal wires. The square ring acts as the “bright state” and the metal wire acts as the “dark state”. The destructive interference between the bright state and the dark state produces an EIT-like effect. In the simulation results, a transparent window centered at 4.00 GHz can be observed in the transmission spectrum. By studying the phase change of the transparent window, it is found that the group delay of the metamaterial structure can reach 0.39 ns at 4.00 GHz. This paper also studies the influence of the refractive index of the medium on the EIT-like effect. Numerical simulations show that such metamaterial is very sensitive to the refractive index of the medium, and the sensitivity is 15 mm/RIU. Our design can be extended to other frequency bands and may have potential applications in filtering, sensing, slow-light devices, and nonlinear optics.

Broadband electromagnetically induced transparency in metamaterials based on hybridization bandgap

We present a broadband electromagnetically induced transparency-like (EIT-like) effect in a microwave waveguide system by employing a bright meta-atom side-coupled to a linear chain of dark meta-atoms with a hybridization bandgap (HBG). We find that such a configuration can generate a wideband EIT response of up to 145 MHz, covering 23.7% of the central frequency. We also show that the EIT bandwidth can even extend to 211 MHz by further broadening the HBG while keeping the device volume unchanged. We emphasize that the EIT-like meta-molecules are subwavelength structures with only about one tenth of the operating wavelength. Our findings will be beneficial for realizing compact broadband slow light components in communication systems.

Tunable Electromagnetically Induced Transparency-Like in Graphene metasurfaces and its Application as a Refractive Index Sensor

We present numerical and theoretical analysis of the tunable electromagnetically induced transparency-like (EIT-like) effect based on graphene metasurfaces. The unit cells of metasurfaces are composed of a pair of parallel graphene strips and a two-split rectangular graphene ring resonator, both of which are performed as bright modes. The physical mechanism behind the EIT-like effect results from the frequency detuning and hybridization coupling of two bright modes. The FDTD simulation results show an excellent agreement with the theoretical analysis based on the coupled Lorentz oscillators model. Moreover, the transparency window of EIT-like effect can be modulated not only by changing the geometry of the nanostructure, but also by adjusting the Fermi level of graphene, allowing for an actively tunable group time delay of the light. In addition, owing to the peak frequency of the transparency window is highly sensitive to the variation of refractive index of the surrounding media, we demonstrate a refractive index sensor with sensitivity of ∼ 6800 nm/RIU, and the calculated FOM can reach up to about 14.2. Therefore, our proposed nanostructure provides a feasible platform for slow light and sensing applications.

Tunable chiral-selective electromagnetically induced transparency-like effect in VO2-based metamaterial for slow light applications

A chiral metamaterial based on vanadium dioxide (VO2) is proposed to realize the ultrafast active control of an electromagnetically induced transparency-like (EIT-like) effect. The design of the tunable metamaterial is based on the heat-induced insulator-to-metal transition of VO2 and a tunable transmission peak with circular polarization selectivity is achieved. For the right circular polarization (RCP) laser incidence, the sharp EIT-like peak is generated and rises with the increasing signal powers, which has not happened in the left circular polarization (LCP) incident condition. The spin-dependent phenomenon in time domain is also observed and the slow light effect in the metamaterial yields a tunable time delay up to 4 ns. Therefore, the tunable EIT-like effect with chiral selectivity is presented and highlights its practical applications in programmable metamaterial regions and slow light devices, etc.

Multiple electromagnetically induced transparency-like effects of a metal nanostructure induced by a graphene grating deposited on a gallium oxide substrate.

The electromagnetically induced transparency (EIT)-like effect can be generated in the metamaterial system, but most metamaterial systems are composed of complex and elaborated components (nanostructures) that cannot be removed or replaced easily. In this paper, a graphene grating is used to interact with random metal nanostructures (i.e., individual and connecting nanostructures) to induce the EIT-like effect through two destructive interference excitation pathways. Except for the new induced EIT-like mode, the overall original optical patterns (the shape and intensity of the transmission spectrum) remain unchanged as compared with the single metal nanostructure. Furthermore, due to the optical properties of graphene, the induced EIT-like effect was blueshifted as the Fermi energy of graphene increased. By depositing the graphene grating and the metal nanostructures on a gallium oxide substrate, the EIT-like effect was redshifted as the temperature of the environment increased. Through this study, the EIT-like effect induced by the graphene grating with a random metal nanostructure system was demonstrated by using a simple geometric system; further, the mechanism is easy and can be introduced to many different metamaterial systems to generate the EIT-like effect without changing other optical properties of the original metamaterial system. As such, this opens the door to broader applications for optical communication networks.