Electromagnetically Induced Transparency Research Articles

Impact of longitudinal magnetic fields on EIT linewidth and dispersive properties in 87Rb vapor

By employing the density matrix approach, this study systematically examines the impact of a longitudinal magnetic field on electromagnetically induced transparency (EIT) within the context of the effective three-level Zeeman sublevels associated with the D 2 -line of 87Rb atomic vapor. Our investigation reveals that a sufficient enhancement in the longitudinal magnetic field induces a discernible narrowing of the EIT linewidth, accompanied by an enhancement in the peak transmission through a Rubidium (Rb) vapor cell. Related to these, we analyse the effect of magnetic field on the dispersive properties of the system, including group delay and group velocity and observed a slight decrement in the group delay and increment in the group velocity, which specifies the transition from slow to fast light under the application of the magnetic field.

Double Resonance of Electromagnetically Induced Transparency of Rydberg Atom in Counter-Propagating Configuration

The double resonance phenomenon of EIT is studied through the ladder three-level Rydberg system. A probe laser with the wavelength λp=852.35 nm is used to coupling the ground state 6S1/2 to the middle state 6P3/2, and a coupling laser with the wavelength λc=509.08 nm is implemented to couple the state 6P3/2 to the Rydberg state 62D5/2. A special optical scheme is designed, in which the co-propagating and counter-propagating configurations are both used. As a result, the double resonance of electromagnetically induced transparency (EIT) with the Rydberg atom is observed. By comparing the distance between the double peaks, it is found that the double resonance phenomenon comes from the Doppler effect, and the distance between the two resonance peaks in the absorption spectrum is related to the detuning of the resonant lasers.

Three-dimensional metamaterial for reconfigurable multi-band electromagnetically induced transparency based on VO2

Conventional 2D planar metamaterials struggle to achieve multi-band electromagnetically induced transparency (EIT) effects due to structural constraints. This paper proposes what we believe to be a novel three-dimensional (3D) metamaterial consisting of a vertical split-ring resonator with vanadium dioxide (VO2) islands at the openings. Based on VO2’s reversible phase transition capabilities, the designed metamaterial has excellent reconfigurability for multi-band EIT effects. When the surface temperature is at room temperature, VO2 exhibits an insulating state. The near-field coupling between bright and dark modes leads to a triple-band EIT effect at 1.72, 1.82, and 1.91 THz, characterized by multi-band, low-loss, and narrowband filtering. In contrast, when the temperature exceeds 68°C, VO2 transitions to its metallic state, resulting in a single transmission window with favorable slow light characteristics. Compared to traditional EIT metamaterials, our work realizes multi-band modulation and switchable operating modes, enhancing flexibility and adaptability. The excellent performance indicates its suitability for various applications, including multi-channel sensors, switchable absorptions, enhancing coupling and slow light devices, etc.

Rydberg atom-based microwave electrometry using polarization spectroscopy

Abstract In this study, we investigated Rydberg atom-based microwave (MW) electrometry using polarization spectroscopy in a room-temperature vapor cell. By measuring Autler-Townes splitting in the electromagnetically induced transparency (EIT) spectrum, we determined that the minimum measurable MW electric field is approximately five times lower than conventional EIT techniques. The results are well reproduced by a full optical Bloch equation model, which takes into account all the hyperfine levels involved. Subsequently, the EIT setup was used to characterize a custom MW cylindrical lens, which increases the field at the focus by a factor of three, decreasing the minimum measurable MW electric field by the same amount. Our results indicate that the combination of polarization spectroscopy and a MW lens may enhance MW electrometry, and may allow its use as a secondary standard.

Tunable electromagnetically induced transparency modulation using L-shaped complementary graphene metamaterials

In this study, we demonstrate the tunable modulation of the electromagnetically induced transparency (EIT) effect using L-shaped complementary graphene metamaterials. The structure consists of a horizontal line slot and a vertical line slot, representing the bright and dark modes, respectively. The synergistic interaction between the bright and dark modes generates a pronounced transparent window within the transmission spectrum. Owing to symmetry, the EIF effect can be realized in two perpendicular polarization directions. Compared to metallic metamaterials, graphene metamaterials are tunable by controlling the Fermi energy of graphene via the gate voltage rather than by redesigning the structure. The regulation of the Fermi energy level in the complementary graphene metamaterials presented herein is more straightforward than that in the discrete graphene configurations. By tuning the EIT transparent window, we enabled actively controlled sensing capabilities and the realization of slow light effects. This work illuminates potential applications in the development of environmental sensors, slow-light devices, and terahertz modulators.

Rydberg electromagnetically induced transparency based laser lock to Zeeman sublevels with 0.6GHz scanning range.

We propose a technique for frequency locking a laser to the Zeeman sublevel transitions between the 5P3/2 intermediate and 32D5/2 Rydberg states in 87Rb. This method allows for continuous frequency tuning over 0.6GHz by varying an applied external magnetic field. In the presence of the applied field, the electromagnetically induced transparency (EIT) spectrum of an atomic vapor splits via the Zeeman effect according to the strength of the magnetic field and the polarization of the pump and probe lasers. We show that the 480nm pump laser, responsible for transitions between the Zeeman sublevels of the intermediate state and the Rydberg state, can be locked to the Zeeman-split EIT peaks. The short-term frequency stability of the laser lock is 0.15MHz, and the long-term stability is within 0.5MHz. The linewidth of the laser lock is ∼0.8 and ∼1.8MHz in the presence and absence of the external magnetic field, respectively. In addition, we show that in the absence of an applied magnetic field and adequate shielding, the frequency shift of the lock point has a peak-to-peak variation of 1.6MHz depending on the polarization of the pump field, while when locked to Zeeman sublevels, this variation is reduced to 0.6MHz. The proposed technique is useful for research involving Rydberg atoms, where large continuous tuning of the laser frequency with stable locking is required.

Classical electromagnetically-induced transparency in hybrid metal-dielectric meta-structures with sub-nanometer linewidth

Metamaterials with parallel electric dipoles (ED) and toroidal dipoles (TD) can be used to cancel the radiations and excite the anapoles. In this paper, a hybrid metal-dielectric meta-structure possessing orthogonal ED and TD has been designed and theoretically studied, which is capable of mimicking electromagnetically-induced transparency effect. The meta-structure consists of horizontal silver rods and vertical silicon plates, where the bright ED modes are induced in the silver rods with a larger Ohmic and radiation loss. In contrast, the dark TD modes can be excited (via near-field coupling) in the silicon plates vertically, which not only own negligible dielectric loss but also prohibit radiation in light propagation direction. The large contrast of loss between the bright and dark modes enables opening of an ultra-narrow transparency window with sub-nanometer linewidth (e.g., 0.023 nm @ 1122 nm), which is comparable with the linewidth of coherent laser sources. The result may be valuable for realizing high-Q resonance, narrow-band light filtering, and slowing light, etc.

Analogue of electromagnetically-induced transparency by toroidal dipole in a symmetry-breaking metamaterial

Analogue of electromagnetically-induced transparency (EIT) in metamaterials was typically based on the destructive interference between electric and magnetic dipolar resonances. In this work, a dipolar toroidal response is demonstrated by a plasmonic metamaterial composed of a ring and a disk. We theoretically demonstrate that the toroidal dipole can couple with the magnetic dipolar response (subradiant mode) and thus induce the EIT-like phenomenon by breaking the geometrical symmetry of the considered metamaterial. The result also shows a promising potential for applications of high-sensitivity resonant transmission associated with the intriguing toroidal moment.

High Q transparency, strong third harmonic generation, and giant nonlinear chirality driven by toroidal dipole-quasi-BIC

Electromagnetically induced transparency (EIT), nonlinearity, and optical chirality hold significant applications in many areas such as optical switches, slow-light devices, chiral harmonic conversion, and optical storage. In this work, we theoretically propose an asymmetric all-dielectric metasurface supporting toroidal dipole-quasi-bound states in the continuum (TD-q-BICs). High quality (Q) EIT, strong third harmonic generation (THG), and giant nonlinear chirality are achieved via the extremely enhanced electric field energy localized in the Si plate by the TD-q-BIC. A huge transition from high Q EIT with transmission of ∼0.99 to strong chirality with circular dichroism (CD) of ∼0.9 is realized by tuning the angle and polarization state of incident light. Strong THG with efficiency of 4.5 × 10−3 under linear polarization light is due to the highly localized electric field supported by the TD-q-BIC and perfect nonlinear CD chirality with theoretically value of ∼1 originates from the large discrepancy in electric field distributions under different circularly polarized light. Our work provides an innovative paradigm to construct TD-q-BICs-governed EIT analogs, THG, and nonlinear chirality for the development of multifunction nanophotonic meta-devices.

Design of tunable terahertz metamaterial for variable optical attenuation and sensing applications

In this work, an actively tunable terahertz metamaterial (TTM) is proposed to realize variable optical attenuation and sensing applications. The unit cell of TTM is composed of H-shaped resonator (HSR) and C-shaped resonator (CSR). The resonant frequency can be tuned from 0.60 THz to 0.82 THz and show an analog electromagnetically induced transparency (EIT) phenomenon. By adjusting the geometry parameters of HSR and CSR, the enhanced quality (Q) factor is obtained from 2 to 14. Moreover, the CSR can be rotated from 0° to 90° to show the potential in the variable optical attenuator (VOA) application. The resonant intensity at 0.60 THz can be gradually decreased and then disappeared eventually when the CSR rotated from 0° to 90° in TE mode. While the resonant intensity at 0.60 THz can be gradually increased and then reach maximum value from 0° to 90° in TM mode. To demonstrate the proposed TTM can be used for the environmental sensing application, the TTM is exposed on the ambient environment with different refractive indexes from 1.0 to 2.2. The maximum sensitivity is 67 GHz. This work offers a novel approach for the THz metamaterial using for the VOA, optical switching, and sensing applications.

Reconfigurable EIT Metasurface with Low Excited Conductivity of VO2

The active materials-loaded reconfigurable metasurface is a potential platform for terahertz (THz) communication systems. However, the requirements of the modulation performance and the modulation rate put forward the opposite requirements on the excited conductivity of active materials. In this paper, we proposed a concept for a metal-doped active material switch that can produce an equivalent high excited conductivity while reducing the required threshold of the active material conductivity, thus balancing the conflict between the two mutual requirements. Based on it, we designed a reconfigurable electromagnetically induced transparency (EIT) metasurface driven by a low excited conductivity of vanadium dioxide VO2, which can achieve the amplitude modulation and amplitude coding under the control of light and electric. Simulation results validate the role of the metal-doped VO2 switch on the metasurface. This work provides a new scheme to mediate the contradiction between the modulation performance and the modulation rate in the requirement of active material’s excited conductivity, which facilitates the development of new terahertz modulators based on reconfigurable metasurfaces. In addition, the concept of a metal-doped active material switch will also provide a solution to the limitations of active material from the design layer.

Reconfigurable Photonic Lattices Based on Atomic Coherence

AbstractThe array of coupled optical waveguides, which is also viewed as a photonic lattice, can exhibit abundant photonic band structures depending on the desired spatial arrangements of involved waveguides. Studies of photonic lattices are usually performed in solid‐state materials, where the required periodic susceptibilities can be achieved by employing the femtosecond laser direct‐writing or optical induction method, and have spawned flourishing achievements in manipulating the behaviors of light. Recently, the concept of electromagnetically induced photonic lattice (EIPL) is proposed under the well‐known electromagnetically induced transparency (EIT) in coherently prepared multilevel alkali‐metal atomic systems, where the strong coupling beams producing EIT possess spatially periodic intensity profiles. The inherited instantaneous tunability of susceptibility from EIT‐modulated atomic coherence allows for the easy reconfigurability of EIPLs, which gives rise to exotic beam dynamics under such a readily controllable framework. This paper summarizes the historical overview and recent advances of the in situ and all‐optically reconfigurable EIPLs. The Introduction section provides the scheme and formation of the EIPL via atomic coherence. The following sections review the recently demonstrated dynamical properties of light in various 1D and 2D EIPLs and in compound EIPLs built by two coupling fields. The final section gives brief concluding remarks.

Control resonant excitation of surface plasmon polariton in quantum-dot molecule system via tunneling induced transparency and Autler–Townes splitting

Electromagnetic induced transparency (EIT) and Autler–Townes splitting (ATS) both produce a transparency window in an absorption profile, yet EIT is distinct in that it can create a transparency window for a weak control field. To elucidate the distinct physical mechanisms underlying EIT and ATS effects, we explore the controlled resonant excitation of surface plasmon polaritons (SPPs) within these regimes. Our setup is composed of three layers: a top vacuum or air layer, a central metal film, and a bottom layer of dielectric medium based on the quantum-dot molecules (QDMs) system. Unlike typical systems, that employ prism or grating coupling scheme, our setup takes advantage of the unique features of the QDMs medium to investigate the direct resonance excitation of SPPs. A weak probe and a strong control field are carried through air or vacuum to the top layer. Our results demonstrate that the permittivity of the bottom medium displays tunneling induced transparency (TIT) if the tunneling strength (Te) and the decay rate of the direct exciton (Γ1) follow the condition Te/Γ1⩽0.5; otherwise, it represents the ATS effect. In both instances, the permittivity of the QDMs medium satisfy the low-loss (high transmission) criteria, i.e., Re [ɛd]<1 and Im [ɛd]≪1, providing a framework for exploring the control resonant excitation of SPPs. We simulate the reflection and transmission spectra using the Fresnel’s formula and noticed sharp dips in reflection and peaks in the transmission spectra, which are the signature of coupler free resonance excitation of SPPs. We noticed that the narrow peak in TIT allows for strong light transmission and thus a high peak in SPP resonance excitation, resulting in higher sensitivity in plasmonic sensors. Conversely, the large spacing between the two peaks in the ATS effect broadens the range of effective excitation frequencies for SPPs, increasing the system’s adaptability and efficiency in applications requiring broad spectrum responses.

Phase-modulation-induced reconfigurable rotating photonic lattices in atomic vapors.

We propose a method to prepare optically induced rotating hexagonal and honey-comb photonic lattices by employing the phase modulated three-beam interference in atomic vapors with electromagnetically induced transparency. The phase differences among the three beams are dynamically elaborated to synthesize the circular motion (in transverse dimensions) of waveguides in the photonic lattices. Further, we verify this model experimentally in the case of low-speed modulation. A weak Gaussian probe field is sent into the constructed helical photonic lattices to image their structures under electromagnetically induced transparency (EIT). The motion trajectories of the sites on the discretized output patterns exhibit repeated circles, advocating the formation of rotating lattices. By introducing phase modulations to involved beams, we provide a continent way for producing transverse motions in waveguide arrays with reconfigurability in rotational direction, radius, and speed. This work looks forward to promising applications in topological photonics with great popularity.

Stretchable kirigami mechanical metamaterial with tunable dual electromagnetically induced transparency resonances

Kirigami, i.e. paper cutting is nowadays widely investigated to design the mechanical structure that can be transformed with unique and programmable performances. When it is transformed, the components of the kirigami are also reconfigured and then provide tunable polarization-sensitive electromagnetic responses. In this study, we present a design of stretchable kirigami mechanical metamaterial (SKMM) with dual electromagnetically induced transparency (EIT) resonances. The proposed two designs of SKMM show two dual EIT resonances at 0.905 THz, 0.975 THz, and 0.449 THz, 0.558 THz, which can be switched to 0.964 THz, 1.042 THz and 0.433 THz, 0.532 THz by rotating kirigami cells in predestinated orientations, respectively. During the continuous modulations of transmission spectra by increasing the stretching force, the characteristics of resonant spectra maintain excellent with their corresponding averaged Q-factors as 33.19, 21.59 and 4.87, 17.31, respectively. The EIT resonances originating from the bright-bright mode could be explained with multipole scattering theory along with the three-dimensional schematic illustrations. These results prove the proposed SKMM possesses promising applications in slow light, optical data computing, quantum information technology, and sensing fields.

Multi-band and polarization-insensitive electromagnetically-induced transparency based on coupled-resonators in a metamaterial operating at GHz frequencies

The analogy of electromagnetically-induced transparency (EIT) has emerged as an intriguing phenomenon in metamaterials research, enabling precise control over electromagnetic wave propagation. In this work, a metamaterial is investigated to achieve polarization-insensitive and multi-band transparency in microwave region. The metamaterial unit-cell consists of three coupled resonators, engineered to exhibit distinct resonance frequencies within the GHz spectrum and their coupling results in transparency windows. The functionality of the metamaterial is validated experimentally, demonstrating dual-band transparency windows at 4.6 and 6.4 GHz. Additionally, under oblique incidence, a third transparency peak arises, and the achieved triple-band EIT peaks can be maintained above 67% up to an incident angle of 60°. Our work contributes a metamaterial platform offering multi-band EIT behavior and polarization insensitivity at GHz frequencies. The proposed structural design leverages coupled-resonator configurations to achieve enhanced control over electromagnetic wave propagation, promising significant advancements in both fundamental research and practical applications. These include advanced signal processing, high-efficiency filters, and sensors operating in GHz communication and radar systems.

Microwave field sensor based on cold cesium Rydberg three-photon electromagnetically induced spectroscopy

Abstract We present the electromagnetically induced transparency (EIT) spectra of cold Rydberg four-level cascade atoms consisting of the 6S1/2 → 6P3/2 → 7S1/2 → 60P3/2 scheme. A coupling laser drives the Rydberg transition, a dressing laser couples two intermediate levels and a weak probe laser probes the EIT signal. We numerically solve the Bloch equations and investigate the dependence of the probe transmission rate signal on the coupling and dressing lasers. We find that the probe transmission rate can display an EIT or electromagnetically induced absorption (EIA) profile, depending on the Rabi frequencies of the coupling and dressing lasers. When we increase the Rabi frequency of the coupling laser and keep the Rabi frequency of the probe and dressing laser fixed, flipping of the EIA to EIT spectrum occurs at the critical coupling Rabi frequency. When we apply a microwave field coupling the transition 60P3/2 → 61S1/2, the EIT spectrum shows Autler–Townes splitting, which is employed to measure the microwave field. The theoretical measurement sensitivity can be 1.52 × 10−2 nV⋅cm−1⋅Hz−1/2 at the EIA–EIT flipping point.

Simultaneously measuring microwave electric fields at different frequencies by Rydberg-atom-based electrometry with Zeeman-resolved Autler–Townes splitting

We provide the simultaneous traceable measurements of microwave electric fields at two different frequencies by the electromagnetically induced transparency (EIT) and Autler–Townes (AT) splitting. A static magnetic field working together with a linearly polarized probe and coupling light prepares Rydberg atoms in Zeeman sublevels with maximal |mJ| in an atomic vapor cell. Using the EIT-AT splitting of these two maximal |mJ| states, the microwave electric fields at two different frequencies are simultaneously measured, in which their frequency difference can be adjustable within the linear range of magnetic field-induced level shifts. The proposed method provides a promising prospect for calibrating multiple microwave frequencies simultaneously in the future.

Plasmonic MIM waveguide based FR sensors for refractive index sensing of human hemoglobin

Fano resonance (FR) is a universal phenomenon that is used to attain electromagnetic-induced transparency (EIT), high absorption and sensitivity, and low-power photonic devices. This work presents dual FR refractive index (RI) sensor models on a plasmonic metal-insulator-metal (MIM) waveguide system. The FR phenomenon is attained by including circular and elliptic nanorod defects in the bus waveguides. The resonances originate from the defect's narrow discreteness and the rectangular resonator's broad state. Analytical methods such as finite difference time domain (FDTD) and multimode interference coupled mode theory are adopted to analyze the FRs. The shapes of the Fano line and resonance peak amplitude can be tuned independently by controlling the diameter of the defects, the separation between the defects, and the coupling (between the resonator and the bus waveguide) distance. Moreover, the proposed structures detect the RI (human hemoglobin) variation in the bus waveguide and resonator. The obtained results with circular nanorod defect verify the autocorrelation coefficient of 99.92 %, ensuring the device's linearity and high performance. However, an autocorrelation of 99.7 % is attained by using two elliptic nanorod defects.

Temporal analogs of electromagnetically induced transparency, induced absorption, and Fano resonance.

We describe the occurrence of electromagnetically induced transparency (EIT), electromagnetically induced absorption (EIA), and Fano resonance due to time-controlled discontinuities in the refractive index of a medium, which leads to the formation of a double-cavity system inside a temporal photonic crystal. The temporal resonances partly resemble the optical resonances arising in conventional microcavities, since the amplified temporal EIA displays distinct spectral characteristics. Although an amplified EIT does not occur, a strongly amplified EIA affects the behavior of EIT as well. Besides modifying the temporal resonances via coupled-cavity interactions, we reveal refractive index-controlled temporal resonances. This computational study paves the way to probe the temporally driven coherent phenomena of EIT and EIA with potential applications such as slow-light, amplified fast-light, amplified ultranarrow bandwidth optical filters, and multicavity systems.