Electromagnetically Induced Transparency Resonance Research Articles

Electromagnetically induced transparency with magnetically induced ΔF=0,mF=0→mF=0 probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to |Fg=F,mF=0⟩→|Fe=F,mF=0⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.

Electrically Injected Metamaterial Grating DFB Laser Exploiting an Ultra‐High Q Electromagnetic Induced Transparency Resonance for Spectral Selection

AbstractThe study shows that, in waveguide (WG) configuration, the coupling of a 2D plasmonic metamaterial grating (MMG) having a conventional Bragg period along the guide but a distinct period along the transverse axis can lead to Electromagnetically‐Induced‐Transparency (EIT) behavior. This epitomizes that metamaterials, as functional photonic building blocks, can lead to low losses in many standard devices if properly designed. The study reported the observation in passive WGs of a marked Fano‐type EIT resonance with record high‐quality factor: Q = 5000 and contrast >20 dB. Unlike any standard metal grating, MMG‐assisted waveguides exhibit strong grating coupling strength and low‐loss properties simultaneously. This concept is further applied to demonstrate single‐frequency‐emission electrically‐injected Distributed Feedback (DFB) lasers in the near‐infrared telecom domain. The key point is that laser emission occurs at the peak of EIT, i.e., the maximum in transmission. It therefore addresses one of the main critical issues of DFB lasers related to the single frequency yield. The laser performances are state‐of‐the‐art (Ith < 20 mA, Pmax > 20 mW at I = 200 mA, SMSR > 50 dB, optical feedback tolerance >−21 dB compliant with IEEE 802.3 standard). The presented approach, compatible with existing industrial technologies, is promising for real‐life telecom applications.

Ultra-wideband terahertz fingerprint enhancement sensing and inversion model supported by single-pixel reconfigurable graphene metasurface

AbstractThe molecular fingerprint sensing technology based on metasurface has unique attraction in the biomedical field. However, in the terahertz (THz) band, existing metasurface designs based on multi-pixel or angle multiplexing usually require more analyte amount or possess a narrower tuning bandwidth. Here, we propose a novel single-pixel graphene metasurface. Based on the synchronous voltage tuning, this metasurface enables ultra-wideband ($$\sim$$ ∼ 1.5 THz) fingerprint enhancement sensing of trace analytes, including chiral optical isomers, with a limit of detection (LoD) ≤ 0.64 μg/mm2. The enhancement of the fingerprint signal ($$\sim$$ ∼ 17.4 dB) originates from the electromagnetically induced transparency (EIT) effect excited by the metasurface, and the ideal overlap between the light field constrained by single-layer graphene (SLG) and ultra-thin analyte. Meanwhile, due to the unique nonlinear enhancement mechanism in graphene tuning, the absorption envelope distortion is inevitable. To solve this problem, a universal fingerprint spectrum inversion model is developed for the first time, and the restoration of standard fingerprints reaches Rmax2 ≥ 0.99. In addition, the asynchronous voltage tuning of the metasurface provides an opportunity for realizing the dynamic reconfiguration of EIT resonance and the slow light modulation in the broadband range. This work builds a bridge for ultra-wideband THz fingerprint sensing of trace analytes, and has potential applications in active spatial light modulators, slow light devices and dynamic imaging equipments.

Electromagnetically induced transparency enabled by quasi-bound states in the continuum modulated by epsilon-near-zero materials.

Highly tunable electromagnetically induced transparency (EIT) with high-quality-factor (Q-factor) excited by combining with the quasi-bound states in the continuum (quasi-BIC) resonances is crucial for many applications. This paper describes all-dielectric metasurface composed of silicon cuboid etched with two rectangular holes into a unit cell and periodically arranged on a SiO2 substrate. By breaking the C2 rotational symmetry of the unit cell, a high-Q factor EIT and double quasi-BIC resonant modes are excited at 1224.3, 1251.9 and 1299.6 nm with quality factors of 7604, 10064 and 15503, respectively. We show that the EIT resonance is caused by destructive interference between magnetic dipole resonances and quasi-BIC dominated by electric quadrupole. Toroidal dipole (TD) and electric quadrupole (EQ) dominate the other two quasi-BICs. The EIT window can be successfully modulated with transmission intensity from 90% to 5% and modulation depths ranging from -17 to 24 dB at 1200-1250 nm by integrating the metasurface with an epsilon-near-zero (ENZ) material indium tin oxide (ITO) film. Our findings pave the way for the development of applications such as optical switches and modulators with many potential applications in nonlinear optics, filters, and multichannel biosensors.

Switchable high-Q electromagnetically induced transparency based on the Ge2Sb2Te5 nanodisk dimers

Bound states in the continuum (BICs) based on metasurfaces have gained significant attention recently to enhance the strength of light-matter interaction. However, most BIC metasurfaces possess fixed optical properties once they have been fabricated. In this study, we introduce the concept of BICs to the phase-change metasurfaces composed of Ge2Sb2Te5 nanodisk dimers. The Ge2Sb2Te5 nanodisk dimers can support a low-Q transverse magnetic dipole resonance, a high-Q toroidal dipole resonance and a high-Q longitudinal magnetic dipole resonance. By adjusting geometric parameter, the high-Q longitudinal magnetic dipole resonance can be converted into a BIC mode. Notably, when Ge2Sb2Te5 is in the amorphous phase, high-Q electromagnetically induced transparency (EIT)-like resonances can be achieved due to the interaction between a low-Q transverse magnetic dipole mode and either a high-Q toroidal dipole mode or a high-Q longitudinal magnetic dipole mode. However, the EIT resonances are switched off when Ge2Sb2Te5 is transformed into the crystalline phase. Furthermore, the high-Q EIT resonances enable the realization of an ultrahigh group refractive index, and can be tuned through the phase transition of Ge2Sb2Te5. The switchable high-Q EIT resonances hold potential applications in slow-light devices, optical modulators, and biosensors.

Active dual-control terahertz electromagnetically induced transparency analog in VO2 metasurface

In this paper, an active dual-control electromagnetically induced transparency (EIT) analog is realized by using vanadium dioxide (VO2) metasurface on a sapphire substrate. The unit cell of the metasurface is a composite-split-ring-resonator (CSRR) composed of two resonators, one of which containing gold pattern and VO2 is named as VSRR and the other containing two T-type resonators is called TTR. The resonant frequency of VSRR and that of TTR are located at 0.43 and 0.75 THz, respectively. While, the CSRR have two resonant frequencies at 0.39 and 0.72 THz, and an EIT-like band has a central frequency at 0.56 THz. When the metasurface is electrically stimulated, the insulator-to-metal-transition (IMT) of VO2 can result in the reconstruction of the metasurface. Therefore, the EIT resonance can be controlled by bias voltages. At central frequency of 0.56 THz, a modulation depth of 87.7% and a group delay of 2.7 ps are obtained. The EIT mechanism is further explained by using a coupled Lorentz model, and theoretical calculation and simulation show good agreement with the experiment. Moreover, by mechanically adjusting the incidence angle, the adjustable EIT-like phenomenon is also observed and the modulation depth achieves 73%. This work paves a way for the development of THz modulators, switches, and slow light devices.

Application of magnetically induced [formula omitted] atomic transitions of cesium atoms in strong magnetic fields

In this work, magnetically induced (MI) transitions of the Cs atoms in strong magnetic fields up to 6 kG, and their applications in spectroscopy are studied experimentally and theoretically. An attractive feature of these transitions is their large frequency shift slope in a magnetic field (−4 MHz/G). Therefore, in strong magnetic fields the frequency shift of MI transitions reaches several tens of GHz and importantly, these transitions do not overlap with others, which is of practical interest for possible use in new frequency ranges. To implement the process of electromagnetically induced transparency (EIT) in a strong magnetic field (1–2 kG), the MI Fg=4→Fe=2 transitions were first used at the frequency of probe radiation, while the frequency of coupling radiation is resonant the Fg=3→Fe=2 transitions. To form the EIT resonance, a cell of sub-micron thickness filled with Cs atom vapors was used, along with strong permanent magnets.

Ultrafast Modulation of THz Waves Based on MoTe2-Covered Metasurface.

The sixth generation (6G) communication will use the terahertz (THz) frequency band, which requires flexible regulation of THz waves. For the conventional metallic metasurface, its electromagnetic properties are hard to be changed once after being fabricated. To enrich the modulation of THz waves, we report an all-optically controlled reconfigurable electromagnetically induced transparency (EIT) effect in the hybrid metasurface integrated with a 10-nm thick MoTe2 film. The experimental results demonstrate that under the excitation of the 800 nm femtosecond laser pulse with pump fluence of 3200 μJ/cm2, the modulation depth of THz transmission amplitude at the EIT window can reach 77%. Moreover, a group delay variation up to 4.6 ps is observed to indicate an actively tunable slow light behavior. The suppression and recovery of the EIT resonance can be accomplished within sub-nanoseconds, enabling an ultrafast THz photo-switching and providing a promising candidate for the on-chip devices of the upcoming 6G communication.

Interplay of polarizations in a cascade EIT system in the presence of vortex coupling light in 87Rb atomic vapor medium

We investigate both experimentally and theoretically the cascade electromagnetically induced transparency (EIT) in configuration in 87Rb atomic vapor medium in the presence of vortex coupling Laguerre Gaussian (LG) light. We demonstrated Doppler free double resonance EIT structure in cascade configuration and observed transmission spectra for and polarized probe and coupling lights. We demonstrate that the double resonance structure can be identified by two photon transition probabilities and it is found to be and . By considering coupling LG light, several polarization combinations are taken into account, and their effects on amplifying and diminishing the EIT resonances are demonstrated experimentally. In order to understand the polarization effects of vortex coupling light on EIT spectrum in a degenerate multilevel atomic system, a theoretical model is developed by considering a simplified double hut level structure. Semi-classical density matrix analysis is used to understand the dynamics and also to establish the enhancement and reduction of EIT peak height with coupling light polarizations. The impact of two photon transition probabilities, polarization combinations and relative orientations of probe and coupling lights in degenerate multilevel atomic systems leads to modification of EIT resonances significantly. We establish quantitative agreement between our theory and experimental results.

Electromagnetically induced transparency for efficient optical modulation in a graphene-dielectric metasurface with surface roughness

A high-performance optical modulator is proposed using a double-layer graphene-based metasurface. A theoretical study of the surface roughness in the proposed modulator is presented for the first time. The metasurface is constructed by a periodic array of double-slit ring resonators adjacent to silicon bars which can support a high quality factor (Q-factor) resonance based on the electromagnetically induced transparency (EIT). The dielectric nano-resonators are deposited on two graphene sheets spaced by a silicon dioxide layer. The modulation voltage is applied across the graphene sheets so that the graphene interband absorption can be adjusted. The proposed modulator is optimized and simulated using the finite-difference time-domain (FDTD) method. According to the presented results, a very high modulation depth of 18.49 dB for a gate voltage of 6.68 V is achieved that is attributed to the strong light-graphene interaction provided by the high Q-factor EIT resonance. To the best of our knowledge, this is the highest modulation depth ever reported for a free-space optical modulator. The 3dB bandwidth of the device is also calculated to be as high as 17.78 GHz. For the sake of completeness, the effect of surface roughness as one of the important fabrication errors is investigated. The performance of the modulator is weakly degraded by surface roughness so that the modulation depth remains higher than 17.1 dB which makes the proposed structure promising for practical realization of free-space optical systems.

Temperature tunable electromagnetically induced transparency in terahertz metasurface fabricated on ferroelectric platform

The integration of active materials in terahertz (THz) metasurfaces is pivotal for the realization of functional device applications in diverse fields like sensing, imaging, communication, etc. In this context, ferroelectric materials endowed with tunable electro-optic properties have recently emerged as a novel candidate for achieving actively tuned THz metasurfaces. Here, we experimentally investigate temperature tuning of electromagnetically induced transparency (EIT) effects in a THz metasurface based on ferroelectric barium titanate (BaTiO3 (BTO)) thin film. We characterize tunable dielectric properties of the BTO thin film under variable temperatures (25 °C–100 °C) at THz frequencies by utilizing THz-time domain spectroscopy technique. Based on this aspect, we design a THz metasurface capable of displaying the EIT effect. THz transmissions through the metasurface sample are then probed for different applied temperatures. The EIT features undergo frequency shifts along with amplitude modulations owing to the temperature induced variations of the dielectric properties of the BTO thin film. A total red shift ∼27 GHz in EIT resonance dip is observed experimentally as the temperature increases from 25 °C to 100 °C. Therefore, we demonstrate utilities of ferroelectric platform toward the development of temperature tunable EIT metasurfaces.

Study of EIT line shape in optically thin and thick media using 87Rb D1 and D2 lines: theory and experiment

In this work, we have presented the variation of the amplitude of electromagnetically induced transparency (EIT) resonances with the density of the atom in a V-type system using 87Rb D1 and D2 lines both theoretically and experimentally. Up to the value of atomic density 18.1 × 1010 cm−3, the amplitude of the EIT resonance gradually increases with the increase of atomic density and then it decreases with the increase of the density of the atom. We have also found the radiation trapping effect in this experiment. We observe the effect of the atomic density on the electromagnetically induced transparency when the systems act as a thin optical media as well as thick optical media. We have found that the amplitude of EIT also depends on pump laser Rabi frequency. Numerical simulations are agreed well with the experimental observations.

Electromagnetically Induced Transparency and Fano Resonances Base on Coaxial Photonic Waveguide Made up of Asymmetric Loop and Resonators

In the actual work, we present the phenomenon of electromagnetically induced transparency (EIT) and Fano resonances by one-dimensional microwave coaxial waveguides for the aim to achieve a filtering system either by transmission or by reflection with very high performance. Our proposed system is composed of coupled asymmetric loops of lengths d2 and d3, and two asymmetric resonators of lengths d5 and d6. This system creates the resonance modes, which are sensitive to certain lengths, while they are insensitive to other lengths. The very narrow EIT resonance appears as a maximum transmission peak stuck between two transmissions zeros, this EIT is due to the interaction of the Eigen modes of symmetric resonators and the incident electromagnetic waves. On the other hand, a resonance near to a zero of transmission is called a Fano resonance, its appearance is due to the interaction between the Eigen modes of symmetric loops and the incoming electromagnetic waves. The theoretical results are obtained using the continuous medium interface response theory, which allows calculating the Green function of composite systems and the transmission rate T. This structure can be utilized for electromagnetic filtering by transmission or reflection with high transmittance and good quality factor. According to these results, this filtering system can be used in the field of microwave communication antennas.

Guiding-mode-assisted double-BICs in an all-dielectric metasurface.

The electromagnetically induced transparency (EIT) effect realized in a metasurface is potential for slow light applications for its extreme dispersion variation in the transparency window. Herein, we propose an all-dielectric metasurface to generate a double resonance-trapped quasi bound states in the continuum (BICs) in the form of EIT or Fano resonance through selectively exciting the guiding modes with the grating. The group delay of the EIT is effectively improved up to 2113 ps attributing to the ultrahigh Q-factor resonance carried by the resonance-trapped quasi-BIC. The coupled harmonic oscillator model and a full multipole decomposition are utilized to analyze the physical mechanism of EIT-based quasi-BIC. In addition, the BIC based on Fano and EIT resonance can simultaneously exist at different wavelengths. These findings provide a new feasible platform for slow light devices in the near-infrared region.

Three port photonic and plasmonic demultiplexers based on Cross and U-shaped stub structures: Application for filtering and sensing

We propose the design of three port photonic and plasmonic demultiplexers where filtering toward the two outputs is based on the phenomena of Fano resonances and electromagnetically induced transparency (EIT). We use a Cross-shape resonator in one output and a U-shape resonator composed of two stubs in the other output. We give a theoretical demonstration of the geometrical parameters of both resonators in order to filter one wavelength in one output while leaving the other output unperturbed. These results are confirmed by experimental validation in the radio frequency domain and a numerical simulation in the infrared (IR) domain using plasmonic metal–insulator–metal waveguides. The Cross resonator in the first output can give rise to an EIT resonance, whereas the U-shaped resonator in the second output may exhibit both EIT and Fano resonances depending on the lengths chosen for the stubs. Therefore, different demultiplexing schemes can be proposed such as achieving a Fano resonance in one output and an EIT in the other, or EIT resonances in both outputs. The Fano resonance is obtained by bringing resonance close to transmission zero, whereas the EIT results from the squeezing of resonance between two transmission zeros. When the widths of the resonances tend to zero, they transform to trapped or bound states in the continuum with an infinite lifetime. We show that the crosstalk between the two channels can be reduced to −82 dB and the sensitivity can reach 2390.8 nm/RIU, RIU is the refractive index units. Finally, we highlight the performance of our design as a high sensitive filter and sensor in the IR domain. In this work, the analytical calculations and demonstrations are performed by using Green’s function approach, the experimental verifications are realized by means of coaxial cables operating in the radio frequency range and the numerical simulations are obtained using the finite element method via Comsol Multiphysics software.

Lineshape Modulation and Sensing Characteristics of Resonator Assembled With Liquid-Metal Core Edge-Coupled With Microfiber Coupler

The resonant response of the hollow microcapillary resonator (HMCR) assembled with liquid-metal core edge-coupled with microfiber coupler (MFC) was theoretically and experimentally investigated. Primarily, for the first time, the analogy electromagnetically induced transparency (EIT) phenomenon and Fano resonance was proposed and discovered in this coupling system. Different from the traditional method, the discrepancy in temperature characteristics of waveguide super-mode and whispering gallery mode (WGM) leads to the evolution of EIT and Fano resonances. This feature has great application value for fiber optic sensors, filters, and switches due to its sharp and asymmetric lineshape. Secondly, the temperature response characteristics were improved by assembling a liquid metal core inside the HMCR. Benefitting from the high thermal expansion-coefficient material, this solution reduces externally imposed energy consumption during the tuning process. In addition to all that, to realize the multi-parameter tuning characteristics, a fiber Bragg grating (FBG) unit was constructed to perform strain tuning. This research has significant implications for sensor measurement, optical filters, optical switches, and optical modulators.

Coherent optical processes on Cs D2 line magnetically induced transitions

The increased spectral resolution allowed by the use of extremely thin vapor cells has led to the observation of interesting behavior of alkali transitions when placed in a magnetic field. Particularly, the probabilities of transitions obeying an apparent Fe−Fg≡ΔF=±2 selection rule, referred to as magnetically-induced (MI) transitions, largely increase in the intermediate interaction regime while being null at zero and higher magnetic fields. With an 800 nm-thick Cs vapor cell placed in a field up to 1.5 kG, we show here that the generation of electromagnetically induced transparency (EIT), realized in Λ-systems involving ΔF=−2 MI transitions, is only possible when both the coupling and probe beams are σ−-circular polarized, demonstrating that EIT is affected by magnetic circular dichroism. A similar rule of thumb can be extrapolated for ΔF=+2 MI transitions and σ+ polarization. Because of the high frequency shift slope (typ. 4 MHz/G), the generation of EIT resonances involving MI transitions is interesting, especially in the context of growing attention towards micro-machined alkali vapor cell sensors.

Electromagnetically induced transparency based on magnetic toroidal mode of dielectric reverse-symmetric spiral metasurfaces

The intriguing properties of the toroidal mode (TM) resonance can potentially promote a low-loss light–matter interaction. This study proposes an electromagnetically induced transparency (EIT) resonance with a high quality factor, which can reach 7798, and low mode volume can reach 0.009 μm3, high contrast ratio can reach nearly 100%, in the near-infrared region, which is generated by the magnetic TM in a reverse-symmetric coupling spiral metasurface. A two-oscillator model can only explain the influence of near-field coupling at the EIT point for weak coupling. Moreover, a multipole decomposition method shows that the excitation mechanism of EIT resonances originates from the destructive interference between the subradiant modes (magnetic toroidal dipole-electric quadrupole) and magnetic dipole resonance. Consequently, a new general extinction spectrum interference model is applied to fit all coupling conditions for both weak and strong coupling results that perfectly correspond to the multipole decomposition method. The results of this study could be useful in the analysis and understanding of the electromagnetic coupling characteristics of nanoparticles and provide a design approach for novel metasurfaces for low-loss optical applications.

Molecularization of meta-atoms for electromagnetically induced transparency resonance and quality-factor switching

Electromagnetically induced transparency (EIT) analogs in terahertz regimes have been actively tuned by hybridizing semiconductors into metasurfaces for effective terahertz manipulation. Although several multiple means have been adopted to modulate EIT, the active control of the EIT quality factor is less reported. Multifunctional EIT modulation should also be considered. In this study, we fabricated a terahertz metadevice by embedding Si bridges into a metasurface with optically controllable molecularization of terahertz meta-atoms and experimentally demonstrated dual-functional terahertz EIT modulation, including resonance amplitude modulation and quality-factor modulation. For a low-power pumping of 16 mW, ultrafast EIT resonance amplitude modulation can be achieved with a low-level molecularization, with a normalized amplitude modulation of up to 85%. Then, with a high-power pumping of 360 mW, we performed ultrafast EIT quality-factor switching, where the high Si-bridge conductivity altered the spatial interconnected structure and exhibited high-level molecularization. Both functions have a nanosecond-scale modulation speed. In addition, we numerically and theoretically explained the terahertz modulation and molecularization behaviors, which was consistent with the experimental results. Our proposed all-optical active terahertz metadevice with controllable molecularization provides a novel solution for multifunctional and ultrafast switchable terahertz modulators.

Effect of closely-spaced excited states on electromagnetically induced transparency

Electromagnetically induced transparency (EIT) is a well-known phenomenon due in part to its applicability to quantum devices such as quantum memories and quantum gates. EIT is commonly modeled with a three-level lambda system; however, this simplified model does not capture all the physics of EIT experiments with real systems. We present a theoretical study of the effect of two closely-spaced excited states on EIT and off-resonance Raman transitions. In addition to the expected broadening of the EIT resonance and reduction in EIT transparency due to multiple excited states, we find some unexpected and interesting results. A comparison with a model that does not allow for coupling of the excited states shows that the coherent interaction of the fields with two excited states whose separation is smaller than their Doppler broadened linewidth can enhance the EIT transparency under some conditions and can enhance and shift the resonance frequency of off-resonance Raman absorption. Furthermore, through a dressed state analysis of the full four-level system, we find that the underlying mechanism for the reduction in EIT transparency is a shift in the two-photon resonance due to unequal dipole moments of the transitions coupled by the control field. Complete transparency can only be recovered for systems with equal dipole moments or when the separation between the two excited states is at least of the order of the Doppler width. To support our theoretical study, we present experimental EIT measurements in the D1 lines of 85Rb and 87Rb that agree with our predictions of an enhancement or reduction of EIT transparency under specific conditions. The experimental results also verify the roles that the dipole moments and the separation between the two excited states have on recovering the EIT transparency.