Thermal Gradient Induced Transparency and Absorption in a Microcavity

An all-optical realization scheme of electromagnetically induced transparency (EIT) in a single silicon optomechanical microring resonator is proposed and demonstrated. Due to the strong mechanical Kerr effect and well-designed microring resonator, two modes with a resonant frequency separation of 292 GHz (2.35 nm) can be tuned into resonance when the control power is about 4.3 µW, and the EIT spectrum is achieved. Our work provides a constructive solution for realizing EIT in a single microcavity with a low mode density. Furthermore, this device is fully integrated on-chip and compatible with current complementary metal-oxide semiconductor (CMOS) processing and has great potential in applications such as light storage, optical sensing, and quantum optics.

Electromagnetically Induced Transparency (EIT), slow light and manipulation of the susceptibility in momentum space have recently been employed to eliminate diffraction during propagation of images in atomic gases [1]. By selecting a two-photon detuning in a Lambda energy-level configuration to be equal to the homogenous EIT linewidth, the induced diffraction compensates the paraxial one and even atomic diffusion [1]. Manipulation and elimination of diffraction is desirable for many applications, such as imaging, microscopy, wave-guiding, microlithography and optical data processing. Here we employ an alternative control of diffraction based on the generation of slow-light dissipative solitons for a three-level medium in a cavity pumped by two quasi-resonant fields. Complex self-organised structures and spatial localization of light due to the interaction of diffraction and nonlinearity in optical cavities have important applications in optics and photonics, ranging from digital optical memories to delay lines [2]. Note that conservative Raman solitons with slow-light have been observed in free propagation in a planar CS2 waveguide by using the localization of a pump field [3].

A terahertz metamaterial structure consisting of two U-shaped split-ring resonators and a horizontal cut-line resonator is designed for realizing the electromagnetically induced transparency (EIT) effect and the Fano resonance effect. The genesis of the EIT and Fano resonance bifunctionality is illustrated by combining the near-field distribution analysis of transparent windows and transmission dips. Interestingly, the bifunctional dual-band transparency effect could transform into a single-functional single-band transparency effect when we change the position of the square metal sheet in the vertical direction of the composited terahertz metamaterial structure. In addition, based on the high-quality factor of Fano resonance response, the proposed bifunctional terahertz metamaterial device has good refractive index sensing sensitivity. These results indicate that our proposed terahertz metamaterial can provide guidance for the design of subsequent multifunctional and integrated metamaterials and optoelectronic devices.

In recent years, the achievement of the electromagnetically induced transparency (EIT) effect based on the guided-mode resonance (GMR) effect has attracted extensive attention. However, few works have achieved a double EIT-like effect using this method. In this paper, we numerically achieve a double EIT-like effect in a GMR system with a three-layer silicon nitride waveguide grating structure (WGS), using the multi-level atomic system model for theoretical explanation. In terms of slow light performance, the corresponding two delay times reach 22.59 ps and 8.43 ps, respectively. We also investigate the influence of wavelength detuning of different GMR modes on the transparent window and slow light performance. Furthermore, a wide-band flat-top transparent window was also achieved by appropriately adjusting the wavelength detuning between GMR modes. These results indicate that the EIT-like effect in the WGS has potential application prospects in low-loss slow optical devices, optical sensing, and optical communications.

A dual-band asymmetric transmission device based on the nonlinear electromagnetically induced transparency (EIT) effect is presented in this paper. The device structure is composed of two P-type branches and two split ring resonators (SRRs). Dual-band EIT effect is induced based on the destructive interferences between scattering fields of the SRRs and branches in a microstrip transmission line system. Moreover, nonlinear varactor diodes and the asymmetric absorption resistor are added to EIT structure based on microstrip line couplings, which results in the asymmetric transmission property. The 10 dB and 7.5 dB transmission light contrasts at the frequencies of 0.85 GHz and 0.95 GHz with the input power of − 3 dBm are demonstrated experimentally. Such low-loss, broadband and high-contrast asymmetric transmission device results from the EIT mechanism, which possesses narrower, sharper and higher transmittance features. Such results will be very beneficial for new nonlinear electromagnetic devices.

Slow light with electromagnetically induced transparency (EIT) in the core of optical fibre containing three-level atoms is investigated. The guided modes are treated in the weakly guiding approximation which renders the analysis into a manageable form. The transparency window and permittivity profile of the core due to the strong pump field in the EIT scheme is calculated. For a specific permittivity profile of the core due to EIT, the propagation constant of the weak signal field and spatial shape of fundamental guided mode are calculated by solving the vector wave equation using the finite difference method. It is found that the transparency window and slow light field can be controlled via the optical fibre parameters. The reduced group velocity of slow light in this configuration is useful for many technological applications such as optical memories, effective control of single photon fields, optical buffers and delay lines.

The electromagnetic induction transparency (EIT) is a phenomenon in which the originally opaque medium becomes transparent under certain resonant electromagnetic fields. It has been seen in applications ranging from nonlinear optics, slow light and optical storage. From the viewpoint of single-frequency, researchers have paid much attention to the realization of broadband electromagnetic induction transparency in recent years. In this paper, a broadband electromagnetic induction transparency effect is investigated theoretically by the finite difference time-domain method. A composite structure based on graphene metasurface which consists of graphene strip with air groove, gallium nitride, silica and titanium dioxide is designed in infrared range. A broadband electromagnetically induced transparency effect could be found in the designed composite structure compared with those in several similar structure. The electromagnetically induced transparency window can be tuned gently by the width of air groove and gallium nitride dielectric slabs. The results show that a wideband electromagnetically induced transparency window of 4 terahertz is found in the infrared frequency range. By comparison with the existing research results, a wider band of electromagnetically induced transparency is found in our structure. We study the physical mechanism of broadband electromagnetically induced transparency from the aspects of structural parameters and electromagnetic field distribution. The thickness w1 of gallium nitride, the width wa and depth h of air groove on graphene strip are discussed in this article. The smaller the length wa or depth h, the wider the EIT band is. The peak of high frequency at which the transmission is near to zero is blue-shifted as h increases. However, red-shift is found as width wa increases. It is found that graphene strip exists as a bright mode. coupling action acts as air groove and gallium nitride slabs function as dark mode, resulting in broadband electromagnetic induced transparency. That is to say, the principle of broadband electromagnetically induced transparency is due to a bright mode coupling in two different forms of dark mode, thus widening the transmission band. This work provides a kind of structure and a design way, to gain the broadband of electromagnetically induced transparency effect. Moreover, it is found that changing the refractive index of background medium, the frequency of high frequency band has a red-shift, the greater change of the refractive index can lead to smaller frequency range. It can be seen that the values of group index ng of three frequency peaks exceeding 25 are observed. The results also show that the slow-light effect and the sensing effect in several frequency ranges are obtained in the proposed structure and potential applications in the optical storage and highly sensitive infrared-band sensor, infrared optical switching, etc.

A three-dimensional structure device that realizes electromagnetic-induced transparency (EIT) in the terahertz band is designed. We use metamaterials to simulate electromagnetic-induced transparency phenomena, through the design of effective metamaterial unit structures, acquire high transmittance while achieving strong dispersion, reducing the absorption of light waves by the medium in the slow light process. EIT’s frequency response is expressed as a narrowband transparent window formed in a large block peak. There are two coupling methods for metamaterials to achieve EIT: bright-bright mode coupling and bright-dark mode coupling. Obviously, the structures in the bright-mode coupled metamaterial unit can be directly excited by incident waves to form a resonant mode, that is, there are at least two radiating mode resonators, which are generally two-dimensional planar structures such as double strips, double rings, etc. This work breaks through the traditional planar patch structure, connects the two resonant rings with cylinders, and innovatively constructs a three-dimensional metamaterial unit. We successfully achieve EIT in the range of 1.06THz to 1.41THz, at a resonance frequency of 1.26THz, the two narrow-band resonance peaks of EIT are located at 1.22THz and 1.30 THz. Realizing EIT through terahertz metamaterials, thereby realizing slow light effect, have paved the way for the design of slow-light devices to meet the future demand for ultra-fast optical signal processing and promote the development of next-generation communication technologies.

We present theoretical and numerical analysis of a plasmonic-dielectric hybrid system for symmetric and asymmetric coupling between silver cut-wire pairs and silicon grating waveguide with periodic grooves. The results show that both couplings can induce electromagnetically-induced transparency (EIT) analogous to the quantum optical phenomenon. The transmission spectrum shows a single transparency window for the symmetric coupling. The strong normal phase dispersion in the vicinity of this transparent window results in the slow light effect. However, the transmission spectrum appears an additional transparency window for asymmetry coupling due to the double EIT effect, which stems from an asymmetrically coupled resonance (ACR) between the dark and bright modes. More importantly, the excitation of ACR is further associated with remarkable improvement of the group index from less than 40 to more than 2500 corresponding to a high transparent efficiency by comparing with the symmetry coupling. This scheme provides an alternative way to develop the building block of systems for plasmonic sensing, all optical switching and slow light applications.

Cavity optomechanical systems have become a topic of great interest in recent years, and the coupled-cavity model is also a classic theoretical framework. This paper aims to construct a coupledcavity optomechanical system to study induced transparency, Fano resonance, and fast-slow light effects in such a system. By transferring phenomena typically studied in a single optical cavity to a coupled-cavity system, we analyze specific phenomena detected in optical and microwave cavities, such as transmission and absorption spectra, to investigate induced transparency. We also examine Fano resonance in the model by varying detuning, and study fast-slow light effects through group velocity. This paper first constructs the corresponding physical model, as shown in Figure 1. Based on the theoretical model, a reasonable Hamiltonian is proposed. By introducing appropriate dissipation and fluctuation noise terms, the Langevin equations of motion are derived. Next, the Langevin equations are linearized, and the resonant terms are retained to obtain <i>O</i><sub>+</sub> . The amplitude of the field modes is then derived using the input-output relations. Following the experimental data from referenced literature, a numerical simulation program is implemented in Mathematica. By substituting the relevant parameters and performing calculations, the results are obtained through simulation. For the first time, the interactions among photons, magnons, microwaves, and phonons— as well as the interplay between photons in the two cavities—are investigated in a coupled cavity optomagnomechanical system. Electromagnetically induced transparency (EIT), Fano resonance, and fast-slow light effects are studied in this coupled-cavity optomagnomechanical framework. Phenomena typically examined in a single optical cavity are extended to the coupled-cavity system, with specific observations analyzed separately in the optical and microwave cavities. When <i>δ</i>=<i>ω</i><i><sub>b</sub></i>, the absorption spectrum splits, and the absorption peak decreases from its maximum to its minimum. This phenomenon arises from the disruption of quantum interference effects. The resonance condition suppresses the generation of Fano resonance. At the resonant frequency <i>ω</i><i><sub>0</sub></i>, the group delay is greater than zero, indicating slow-light propagation, and this effect is enhanced with increasing coupling strength. Additionally, a group delay of τ is achieved. Meanwhile, on either side of the resonant frequency, the group delay peaks exhibit a decreasing positive value and an increasing negative value, respectively, signifying a gradual weakening of the slow-light effect and a corresponding enhancement of the fast-light effect. This paper investigates the MIT, MMIT, and OMIT windows in a coupled-cavity optomagnomechanical (OMM) system under a strong control field and weak probe field. The MMIT phenomenon is observed through nonlinear phonon-magnon interactions. Additionally, the photon-magnon interaction in the microwave cavity leads to MIT, while OMIT is achieved via the radiation pressure interaction between photons and nonlinear phonons in the optical cavity. The frequency of the probe field is tuned to interact with both the microwave and optical cavities. When the probe field couples with the microwave cavity, its absorption at the resonant frequency is significantly suppressed under optomechanical coupling, resulting in a pronounced optical switching effect on transmission. We analyze the asymmetric Fano resonance phenomenon, which reflects the existence of quantum interference mechanisms within the system and influences the fast- and slow-light conversion processes. Furthermore, by selecting appropriate coupling parameters, not only can the fast- and slow-light effects be enhanced, but dynamic switching between them can also be achieved.

Well-established electromagnetically induced transparency (EIT) and absorption (EIA) have been applied to various applications including quantum computing, light storage, and precision measurement. Here, we propose and implement a differential detection scheme based on coexisting EIT and EIA signals in a double-Λ system with counterpropagating bichromatic laser fields, in which a differential coherent population trapping (diff-CPT) signal is extracted with a desired enhanced amplitude and highly suppressed common-mode noise. Compared to that of either EIT or EIA, the observed signal-to-noise ratio of the proposed method’s diff-CPT signal improved by one order of magnitude, which would benefit the implementation of high-performance CPT clocks. This technique may also be applied to magnetometers and precision spectroscopy.

Metasurfaces emerge as exceptional platforms for achieving classical‐analog electromagnetically induced transparency (EIT). In this study, dual‐band EIT is demonstrated by strategically engineering the coupling between a magnetic toroidal dipole (TD) Mie resonance and two quasi‐bound states in the continuum (QBICs) within all‐dielectric metasurfaces. Through deliberate symmetry breaking in the cuboid unit cell—achieved via off‐center holes or U‐shaped configurations—two BICs, predominantly governed by electric TD and magnetic quadrupole modes, are successfully transformed into QBICs with high quality (Q) factors. These QBICs are then coupled to a low‐Q magnetic TD Mie resonance, resulting in the emergence of dual‐band EIT. The corresponding group delays reach up to 9.51 ps (Q = 7,674) and 5.69 ps (Q = 3,631), respectively, and diverge when the Q‐factors approach infinite. Furthermore, the dual‐band EIT with high Q‐factors is experimentally validated by fabricating a series of silicon metasurfaces and characterizing their transmission spectra. Excellent agreement is found between numerical simulation and experimental measurement. Measurement results reveal that both the resonance wavelengths and Q‐factors of the dual‐band EIT are precisely tuned by adjusting the asymmetry parameters. These findings hold significant promise for applications in multi‐wavelength slow light devices and biosensing.

Triple-band graphene-based tunable electromagnetically induced transparency terahertz metamaterial with multi-frequency optical switching

This article investigates and improves optical properties of slow light devices. The device structure consists GaAs/AlGaAs [110] strained quantum wells (QWs) based on V-type electromagnetically induced transparency (EIT). In this paper, we use an analytical model in fractional dimension in order to simulate and analysis slow light device. Effects of well width variation have been investigated on exciton oscillator strength (EOS) and fractional dimension parameter. Influences of these parameters alterations have been illustrated in optical properties of slow light system such as slow down factor (SDF) and central energy of the device. Based on obtained results, we can adjust optical variables of slow light system with controlling the well thickness. Using proposed method, we have also estimated the maximum value of SDF about 9×103.

All-optical group velocity manipulation of light, so-called slow and fast light, has drawn extensive attention due to its potential applications in the fields of optical signal processing, light storage, light-matter interaction enhancement, hypersensitive sensing and temporal cloak. Tremendous approaches of slow and fast light generation have been widely demonstrated by the creation of the sharp spectral resonances in the past decade. Specifically, superluminal propagation (larger-than-light velocity c ) through the optical media has been proposed and validated in anomalous dispersion media. One effective approach is employing stimulated Brillouin scattering to harness the narrowband spectral resonance and thus generate slow and fast light in the optical fiber. In particular, Brillouin lasing oscillation has been experimentally demonstrated to generate fast and superluminal propagation in ten-meter optical fibers. Afterwards, the propagating distance over hundreds of meters has been experimentally demonstrated by the suppression of multiple-longitudinal-mode operation. However, the delay-bandwidth product or the fractional advancement is still fundamentally limited in conventional fast and slow light system. For example, the maximum advancement as well as the fractional temporal advancement are practically restricted due to the Brillouin gain saturation and multiple longitudinal mode lasing operation under high pump power in the Brillouin lasing resonance-based fast and superluminal system. In this paper, we experimentally validate the extension of time advancement of superluminal propagation based on Brillouin lasing oscillation for the first time. By employing two stages of single-frequency Brillouin lasing fiber ring resonators, Stokes lasing resonance was effectively created in each fiber ring cavity to deliver Brillouin-induced loss resonance at the center frequency of pump, which essentially leads to fast light and superluminal propagation of the pump light. Consequently, Gaussian signal pulses with the pulse width of 500 ns experiences cascaded Brillouin-induced fast light and even negative group-velocity superluminal propagation. The temporal advancement was basically extended to 365.8 ns which is twice than that of single stage fast light and superluminal system. Correspondingly, the fractional advancement was increased from 0.36 to 0.73. The maximum group velocity was 6.3 times larger than the light speed c in vacuum while negative-group- velocity propagation can be found in the range of −9.9 to −0.2 by increasing the total input power from 593.2 to 812.0 mW. Furthermore, the group index can be manipulated in the range of 1.5 to −4.0 by simply varying the total input pump power. It indicates superluminal signals can be cascaded to essentially extend the propagation distance and enlarge the temporal advancement. The scheme exhibits robustness in cascading Brillouin spectral loss resonance for temporal advancement enhancement as well as propagating distance extension. More importantly, the cascading design could basically eliminate the fundamental limitation introduced by Brillouin gain saturation and multiple longitudinal lasing mode under high power operation in single stage Brillouin fast and superluminal system. Further optimization could also be implemented by utilizing the nonstandard specialty fibers as Brillouin gain medium to achieve an efficient Brillouin lasing resonance for an enhanced advancement efficiency. Additionally, the combination with the cascading technique and long-cavity single-frequency Brillouin lasing resonance could enable the feasibility of distance-limitless and large-advancement superluminal propagation, paving a way for promising applications in sensing and temporal cloak.