Electromagnetically Induced Transparency Resonance Research Articles

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.

Active modulation of electromagnetically induced transparency analog in graphene-based microwave metamaterial

Metamaterial analogs of electromagnetically induced transparency (EIT) enable a unique route to enhance light-matter interactions without quantum approach, showing remarkable potentials for slow-light devices and highly sensitive sensors. In particular, dynamic control of EIT in metamaterials opens new avenues for optical networks and electromagnetic communications. Here, we experimentally present, for the first time, the active modulation of EIT analog by integrating graphene into a microwave metamaterial. Experimental results demonstrate that the EIT peak can be dynamically controlled under a relatively low bias voltage applied on graphene. A coupled harmonic oscillation model is exploited to analyze the physical mechanism which lies in the active tuning of the damping rate of the dark mode resonator through varying the graphene's sheet resistance. Via variably dampening the dark resonator using graphene, the coupling condition could be electrically modulated and the continuous tuning of the EIT resonance strength is achieved. In addition, the controllable slow-wave propagation is also performed theoretically based on the tunable phase delay of the transmitted waves. This work opens up promising possibilities for slow-wave manipulation with applications in smart and multifunctional devices.

Dual-band electromagnetically induced transparency (EIT) terahertz metamaterial sensor

We propose a dual-band terahertz metamaterial sensor (MS), which exhibits the low loss and high quality (Q) factor of electromagnetically induced transparency (EIT) effects at the frequencies of 0.89 THz and 1.56 THz simultaneously. The physical natures of EIT effects are analyzed by using numerical simulations and a “two particle” model. Further, THz sensing is performed based on the shifts of two EIT resonances when the analyte is coated at the metamaterial surface. The sensitivities of the sensor are investigated with respect to different thicknesses, cover areas and refractive indexes of the coated analyte film. Results show that the first EIT resonance is suitable for sensing the analyte with the refractive index from 1.5 to 2, while the second EIT resonance is more suitable for sensing the refractive index of the analyte from 1 to 1.5. The sensitivity is 280.8 GHz/RIU, the average Q value is 14.3, and the figure of merit (FOM) value is 4 for the first EIT resonance. Meanwhile, the sensitivity is 201.6 GHz/RIU, the average Q value is 56.9, and the FOM value is 11.5 for the second EIT resonance. Such a metamaterial sensor with high refractive index sensitivity and dual-band would have great potentials for promoting the developments of multi-band/broadband terahertz sensing and detection technology.

Two-color optical nonlinearity in an ultracold Rydberg atom gas mixture

We report the experimental observation of strong two-color optical nonlinearity in an ultracold gas of $^{85}\mathrm{Rb}$-$^{87}\mathrm{Rb}$ atom mixture. By simultaneously coupling two probe transitions of $^{85}$Rb and $^{87}$Rb atoms to Rydberg states in electromagnetically induced transparency (EIT) configurations, we observe significant suppression of the transparency resonance for one probe field when the second probe field is detuned at $\sim1~\mathrm{GHz}$ and hitting the EIT resonance of the other isotope. Such a cross-absorption modulation to the beam propagation dynamics can be described by two coupled nonlinear wave equations we develope. We further demonstrate that the two-color optical nonlinearity can be tuned by varying the density ratio of different atomic isotopes, which highlights its potential for exploring strongly interacting multi-component fluids of light.

Surface plasmon polaritons broadband band-stop filter based on EIT effect modulation

The filter is one of the most important key elements of electronic circuit. With the rapid development of information, traditional electrical filters can no longer meet the requirements of fast information processing speed and low loss. All optical information processing is considered as one of the solutions to solve this problem. Therefore, there is great significance for studying the all-optical filter. Here, we put forward a kind of broadband band-stop filter which based on surface plasmon polaritons (SPPs) metal - insulator - metal (MIM) modulating by electromagnetically induced transparency (EIT) resonance. We use the finite element method for numerical simulation, and further research on the factors influencing the transmission characteristics of this structure by adjusting the geometric structure. Compared with similar SPPs-based filters, the proposed structure realizes broad stopband, and we can change the EIT resonance to modulate the band-stop filter wavelength range. The proposed broadband band-stop filter based on EIT effect modulation may have great potential in the next generation of all-optical information processing and communication.

Band-stop filter based on tunable Fano resonance and electromagnetically induced transparency in metal-dielectric-metal waveguide coupling systems

Metal-dielectric-metal (MIM) waveguide coupling systems based on surface plasmon polaritons (SPPs) are designed and studied. The finite element method is used to simulate the transmission spectra of structures in the whole simulation process. One waveguide coupling system consists of an inverted T-shaped cavity with defect (ITD) and a waveguide with a metal wall. The filter band appears in the transmission spectrum due to the opposite direction of two Fano resonances. The filter band width and the filtering range can be tuned effectively by changing the structure parameters. In this system, the center frequency and bandwidth of the filter band are 1330 nm and 114 nm, respectively. The insertion loss and reflection loss are −1.41 dB and −16.89 dB, respectively. The optimization is carried out on the basis of the first system in order to improve the filtering performance. Optimized waveguide coupling system contains an ITD and a waveguide with a slot cavity. Electromagnetically induced transparency (EIT) and Fano resonance exist simultaneously, and the filter band is induced in the transmission spectrum. In this system, the center frequency and bandwidth of the filter band are 1412 nm and 120 nm, respectively. The insertion loss and reflection loss are −0.50 dB and −37.32 dB, respectively. EIT and Fano resonance can not only be regulated independently, but also be regulated simultaneously by changing the structural parameters. And the intensity of EIT and the width of the filter band can be manipulated with changes of the structural parameters. The transmission response of SPPs propagating in the structure can be adjusted dynamically. Moreover, these novel SPPs optical waveguide structures have good filtering efficiency and can meet different filtering needs. These results show that the proposed systems are promising for filter, slow light device and photonic device integration applications.

Active control of electromagnetically induced transparency analog in all-dielectric metamaterials loaded with graphene

Electromagnetically induced transparency (EIT) analog in all-dielectric metamaterials with a high quality factor provides an effective route to enhance light–matter interaction at the nanoscale. In particular, the active control applied to it enables great degree of freedom for spatial light modulation and thus promises functional device applications with high flexible tunability. Here, we load graphene into all-dielectric metamaterials and realize the remarkably high modulation depth in the transmission amplitude of the EIT resonance with the manipulation of graphene conductivity, via shifting the Fermi level or altering the layer number. The physical origin lies in the controllable light absorption through the interband loss of graphene in the near infrared. This work reveals a strategically important interaction mechanism between graphene and EIT resonance in all-dielectric metamaterials, and opens avenues in designing a family of hybrid metadevices that permit promising applications to light modulation, switching, slow light and ultrasensitive biosensing.

Doppler narrowing, Zeeman and laser beam-shape effects in Λ-type electromagnetically induced transparency on the 85Rb D2 line in a vapor cell

We study Λ-type Electromagnetically Induced Transparency (EIT) on the Rb D2 transition in a buffer-gas-free thermal vapor cell without anti-relaxation coating. Experimental data show well-resolved features due to velocity-selective optical pumping and one EIT resonance. The Zeeman splitting of the EIT line in magnetic fields up to 12 Gauss is investigated. One Zeeman component is free of the first-order shift and its second-order shift agrees well with theory. The full width at half maximum (FWHM) of this magnetic-field-insensitive EIT resonance is reduced due to Doppler narrowing, scales linearly in Rabi frequency over the range studied, and reaches about 100 kHz at the lowest powers. These observations agree with an analytic model for a Doppler-broadened medium developed in (Javan et al 2002 Phys. Rev. A 66 013805; Lee et al 2003 Appl. Phys. B, Lasers Opt. (Germany) B 76, 33–9; Taichenachev et al 2000 JETP Lett. 72, 119). Numerical simulation using the Lindblad equation reveals that the transverse laser intensity distribution and two Λ-EIT systems must be included to fully account for the measured line width and line shape of the signals. Ground-state decoherence, caused by effects that include residual optical frequency fluctuations, atom-wall and trace-gas collisions, is discussed.

Manipulating EIT and EIA Effects by Tuning the Gain Assisted Dark Mode

We investigate the scattering properties of an array of plasmonic structure consisting of a bright atom and a gain assisted dark atom. In light of the Lorentz model analysis, we demonstrate perfect electromagnetically induced transparency (EIT) like resonance with high Q factor when proper amount of gain is introduced. The non-Hermitian physics associated with the proposed structure can greatly enrich the electromagnetic property of it. Ultra-high transmission and reflection of a finite bandwidth are reported at the EIT resonance frequency when the gain level is increased to a critical point. Furthermore, we find that by introducing extra loss into one strip and equal amount of gain into another strip in the dark atom simultaneously, enhanced absorption of the incident wave is achieved. In addition to incorporating material gain to balance the loss, we propose that coherent pump waves can introduce effective gain in the dark mode. Compared to utilizing gain medium, such a route is much easier to implement. The demonstrated high-Q EIT resonance, lasing and enhanced absorption effects may find their applications in sensing, switching, absorbing, nonlinear optics and spaser areas.

Switchable Electromagnetically Induced Transparency with Toroidal Mode in a Graphene-Loaded All-Dielectric Metasurface.

Active photonics based on graphene has attracted wide attention for developing tunable and compact optical devices with excellent performances. In this paper, the dynamic manipulation of electromagnetically induced transparency (EIT) with high quality factors (Q-factors) is realized in the optical telecommunication range via the graphene-loaded all-dielectric metasurface. The all-dielectric metasurface is composed of split Si nanocuboids, and high Q-factor EIT resonance stems from the destructive interference between the toroidal dipole resonance and the magnetic dipole resonance. As graphene is integrated on the all-dielectric metasurface, the modulation of the EIT window is realized by tuning the Fermi level of graphene, engendering an appreciable modulation depth of 88%. Moreover, the group velocity can be tuned from c/1120 to c/3390. Our proposed metasurface has the potential for optical filters, modulators, and switches.

Ultrafast Frequency Shift of Electromagnetically Induced Transparency in Terahertz Metaphotonic Devices

AbstractRecently, the actively controlled meta‐atoms have been employed to manipulate terahertz (THz) waves allowing for the implementation of many functionalities operating. A salient example of such systems is the electromagnetically induced transparency (EIT) metaphotonic device, which opens up a new avenue for THz manipulations. However, these devices are currently limited to be tuned at a given frequency, which severely impedes their practical applications. Here, novel photo‐active THz meta‐atoms are proposed, whose EIT resonance is equipped with a frequency tuning functionality up to 36%. At different levels of optical pumping power, a substantial modulation of EIT resonance is realized at the fundamental and shifted frequency, respectively. Moreover, the ultrafast dynamics manifest the switching time scale of ≈1 ns. This configuration is easily extensible by other types of stimuli, which may contribute to the development of multifunctional active tuning meta‐photonic systems.

Ion Imaging via Long-Range Interaction with Rydberg Atoms.

We demonstrate imaging of ions in an atomic gas with ion-Rydberg-atom interaction induced absorption. This is made possible by utilizing a multiphoton electromagnetically induced transparency (EIT) scheme and the extremely large electric polarizability of a Rydberg state with high orbital angular momentum. We process the acquired images to obtain the distribution of ion clouds and to spectroscopically investigate the effect of the ions on the EIT resonance. Furthermore, we show that our method can be employed to image the dynamics of ions in a time resolved way. As an example, we map out the avalanche ionization of a gas of Rydberg atoms. The minimal disruption and the flexibility offered by this imaging technique make it ideally suited for the investigation of cold hybrid ion-atom systems.

Artificial modulation-free Pound-Drever-Hall method for laser frequency stabilization.

We have proposed an artificial modulation-free Pound-Drever-Hall (PDH) method for laser frequency stabilization and demonstrated it via two-color polarization spectroscopy of Rydberg electromagnetically induced transparency (EIT) resonance in a room-temperature rubidium vapor. Due to the unique error signal profile, the conventional PDH method owns a large capture range in laser frequency locking. Here we manually construct a PDH error signal via a linear combination of polarization spectroscopies of the Rydberg EIT resonances without and with a magnetic field applied. The artificial modulation-free PDH error signal owns a subnatural linewidth dispersion curve as well as a large capture range with which we successfully stabilize the laser to an absolute atomic frequency reference in a long running time, immune to environmental fluctuation and even manmade impulse perturbation. This method can provide an absolute frequency reference based on atomic transition while keeping similar locking ability to provide corrections for frequency fluctuations over a broad bandwidth as the conventional PDH.

Ultrahigh-quality electromagnetically induced absorption resonances in a cesium vapor cell

Electromagnetically induced absorption (EIA) of cesium atoms exposed to counter-propagating light waves with orthogonal linear polarizations is studied. Probe beam transmission through a buffer gas-filled vapor cell is monitored as a function of a static magnetic field applied parallel to the wave vectors. The light waves are tuned to a single dipole transition Fg → Fe in the D1 line (λ = 894.6 nm). The proposed magneto-optical configuration helps overcome a long-standing problem in obtaining high-contrast EIA resonances in conjunction with narrow linewidths. Our experiments demonstrate EIA contrast with respect to a broad Doppler absorption background (CD) as high as 1630%. Thus, a high value of CD means that background absorption is almost absent, and the vapor cell transmission profile represents only a single narrow resonance. This result is unique for EIA as well as for electromagnetically induced transparency (EIT) effects, because usually in a resonant medium, narrow EIT or EIA resonances are accompanied by natural-linewidth or other broad spectral features, even in the case of cold atoms. The resonance contrast with respect to the light transmission background (Cback) is also high enough, reaching 75% in the experiments. The full width at half maximum of the narrowest observed EIA is approximately 0.77 mG (0.7 × 0.77 = 540 Hz in the frequency domain). The considered simple scheme has good prospects for the development of various quantum magneto-optical devices such as optical switches and atomic magnetometers.

Active control of electromagnetically induced transparency based on terahertz hybrid metal-graphene metamaterials for slow light applications

Recently, the dynamically controlled electromagnetically induced transparency (EIT) metamaterials have been widely used in the slow light effect field to enhance the light-matter interactions and nonlinear effects, which has aroused the great attraction of many researchers. The emergence of two-dimensional materials has pushed this research to a new research hot again. Therefore, a terahertz hybrid metal-graphene metamaterial, consisting of a bi-layer metallic EIT metamaterial, an unpatterned monolayer graphene, and an encapsulated ion-gel layer, was proposed to actively control the EIT resonance. In this structure, the transparency peak of the bi-layer metallic EIT metamaterial can realize on-to-off switch through shifting the Fermi energy of graphene covering onto the dark mode resonators. Theoretical analysis and surface current distributions reveal that the active modulation can be attributed to the increasing damping rate of the dark mode caused by the actively controllable conductivity of the graphene. In addition, the active control of the group delay in the hybrid metamaterial is also demonstrated for the slow-light applications. Therefore, this work provides an alternative way to design compact slow-light devices for future terahertz wireless communications.

Enhanced THz EIT resonance based on the coupled electric field dropping effect within the undulated meta-surface

Abstract In this paper, the enhanced terahertz (THz) electromagnetically induced transparency (EIT) resonance is achieved based on the coupled electric field dropping effect within the undulated meta-surface. It is found that the height difference between the inner ring and the outer split ring could lead to a significant coupled mode with electric field dropping distribution. When the height of the inner ring increases, the electric field of the inner ring gradually cascades to the outer ring just as a waterfall so that the coupling between the two rings in a unit cell and two adjacent units is enhanced. Both the simulation and experimental results show that a nearly 95% transparency window which is twice that of traditional EIT can be observed by applying such coupled electric field dropping effect, which may provide a promising way to develop the high resonance intensity meta-surface in the THz region.

Tailoring slow light with a metal–graphene hybrid metasurface in the terahertz regime

A metal–graphene hybrid metasurface is proposed and numerically investigated for active tailoring of slow light in the terahertz (THz) regime. In the unit cell of the metasurface, four mirror-symmetrically arranged aluminum split ring resonators (SRRs) form the bright-dark-dark-bright mode coupling and exhibit a strong electromagnetically induced transparency (EIT) resonance characteristic. With monolayer graphene placed under the dark SRRs, both the transmission amplitude of EIT resonance and the group delay within the transparency window can be continuously tuned via shifting the Fermi level of graphene. Further theoretical analyses reveal that the active modulation arises from the increasing damping rate of the dark SRRs due to the recombination effect of the conductive graphene. The proposed metasurface provides an effective approach to tailoring the slow light effect and will find important applications in active functional devices for future THz wireless communications.

High spectral purity electromagnetically induced transparency-based microwave optoelectronic oscillator with a quasi-cylindrical microcavity.

High spectral purity microwave oscillators are widely exploited in science and military areas including communication, radar, and navigation. Here, we theoretically analyze and experimentally observe the application of tunable electromagnetically induced transparency (EIT) effect generated within a single quasi-cylindrical microresonator (QCMR) to a high spectral purity microwave optoelectronic oscillator (OEO). Stable single-frequency microwave oscillation with phase noise of -123 dBc/Hz at 10 kHz offset from ~5 GHz carrier and -135 dBc/Hz at 100 kHz offset is demonstrated without using any narrow-band RF filters. Moreover, we evaluate the impact of laser-mode locking state, quality factor as well as spectral lineshapes of the EIT resonance, laser coupling efficiency, and three configurations of optical energy storage elements on the spectral purity of the oscillator, so as to improve its phase noise and stability performances. Extending the concept of EIT to a microwave generator opens a promising avenue towards compact low-phase-noise oscillator systems for emerging mass applications.

Study of EIT resonances in an anti-relaxation coated Rb vapor cell

We study the sign of resonances obtained in electromagnetically induced transparency (EIT). Resonances of both kinds—bright (corresponding to enhanced absorption) and dark (corresponding to reduced absorption)—are obtained when the frequency of a probe beam is scanned. The experimental results, presented earlier, use magnetic sublevels of a hyperfine transition in the D1 line of 87Rb along with a magnetic field of 27 G. The atoms are contained in a vapor cell at room temperature, and with anti-relaxation coating on the walls. A quantitative theoretical model, which reproduces the experimental results quite well, is presented for the first time. The model solves the density matrix of the sublevels involved, and uses two regions—one with both the light and magnetic field, and the second without light and just a magnetic field. This ability to have both bright and dark resonances promises applications in sub- and super-luminal propagation of light.