Slow Light Phenomenon Research Articles

Tunable Fano resonance in a novel compact metal–insulator–metal structure

A novel compact scheme to realize tunable Fano resonance is proposed and investigated theoretically and numerically. The scheme is based on two slot cavities in a metal–insulator–metal structure. The model and formation mechanism of Fano resonance in this structure are studied. A new method based on four-mode temporal coupled-mode theory is used to analyze model of the structure with two slot cavities. Compared with previous studies, this method only considers the interaction between modes within two cavities rather than considering the energy coupling between them. The tunability and slow light phenomenon in the new structure are also studied. It is believed that research in this article can provide a new method to achieve Fano resonance. Furthermore, it is helpful to establish the Fano resonance model and reveal the formation mechanism of Fano resonance.

Chirp-driven control over fast-slow light effects in epsilon-near-zero metamaterials.

Optical applications based on fast and slow light effects force the usage of metamaterials famous for their flexible dispersion properties. In this work, we apply the unique optical nonlocality of metal nanorod-based epsilon-near-zero (ENZ) metamaterials along with the chirp of femtosecond laser pulses for astonishing control of these effects. We demonstrate the switching between the fast and slow light phenomena via the change of the angle of incidence and/or the central wavelength of chirped pulses in the vicinity of metamaterial zero-transmission regime mediated by the ENZ nonlocality. We elucidate that the laser chirp allows one to manipulate and enhance the fast-slow light phenomena.

Sequential infiltration of two-photon polymerized 3D photonic crystals for mid-IR spectroscopic applications

Photonic crystals (PhCs) are spatially organized structures with lattice parameters equivalent to the operational wavelength of light. PhCs have been subject to extensive research efforts in the last two decades and are known for controlling light propagation with applications in sensing and time-delayed communication due to the slow-light phenomenon. Despite their exceptional properties, PhCs are difficult to fabricate using planar micromachining techniques due to their periodic structures. Techniques like two-photon stereolithography have been discussed for PhC fabrication in the literature, but the inherent disadvantage of poor refractive index (RI) contrast results in limited application. In this work, we present sequential infiltration synthesis performed on two-photon stereolithographically printed 3D PhCs for infiltration with zinc oxide to increase the RI of 3D PhCs. Finite element analysis was performed over a range of RI contrast values to study the change in photonic bandgap (PBG) with RI contrast. The transmission spectra were recorded on 3D PhCs before and after infiltration to demonstrate the change experimentally. An increase in the PBG width and absorbance is seen postinfiltration due to enhanced RI. This work presents the first, to our knowledge, sequentially infiltrated enhanced 3D PhC fabricated with two-photon stereolithography.

Dispersion-dependent superluminal propagation and photon drag in GaAs/AlGaAs quantum dot molecule

Controlling the basic properties of light such as polarization, angular momentum, and speed through various optical media leads to interesting phenomena in various fields such as quantum optics, photonics, plasmonics, and quantum information technology. Few of the phenomenon include, for instance, light storage, ultra-slow and ultra-fast propagation, optical transparency, and quantum entanglement via quantum coherence or superposition. The understanding of these phenomenon of milestone implications paved the way for the invention of novel classical and quantum technology. In this article, we present detailed theoretical and numerical demonstration on the dispersion-dependent phenomenon of slow and fast light, optically induced transparency, and photon drag. For this, we employ a three-level scheme of an ensemble of GaAs\\AlGaAs double quantum dot molecule in cascade configuration. In particular, by tuning the medium dispersion we predict interesting interplay between ultra-slow and ultra-fast light propagation with vanishing, infinite, ultra-positive and ultra-negative group velocities, and optical-assisted quantum transparency. The quantum coherence of the dressed states modifies considerably the optical properties of the system in view of dispersion, absorption, electron energy loss, transmission, and photon drag. An interesting interplay between ultra-slow to ultra-fast propagation is found by tuning various optical parameters. The calculated superluminal value of group velocity is m s−1. We also predict light propagation at vanishing and infinite group velocity. The calculated light drag is rad/m.

Flexible all-optical terahertz switch based on electromagnetically induced transparent-like metamaterial

The electromagnetically induced transparent-like metamaterials have received much attention because of their excellent slow-light properties and strong nonlinear effects. They have many promising applications in novel terahertz functional devices, high-sensitivity sensors, and optical storages. In this paper, a flexible terahertz switching device based on the electromagnetically induced transparent-like effect was proposed. The device exhibited a significant slow light phenomenon without pumped laser. Meanwhile, it is demonstrated that the device has a large modulation depth and excellent tunable slow light performance with low-power pumped laser. Its amplitude modulation depth can reach 60.4% and the group delay modulation can reach 32.5 ps. And the minimum group velocity of the device in slow terahertz light can reach 0.69 × 105 m/s. Moreover, the flexible substrate of the proposed device is not easily damaged. It makes the device suited for more complex environments well. Therefore, the device will have great potential for future research on high-performance terahertz switching devices.

Analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency with high sensitivity based on simple circular ring resonators and vanadium dioxide film

An analogy of polarization-independent, multi-band and tunable electromagnetically induced transparency (EIT) effect is proposed based on simple combination of circular ring resonators and vanadium dioxide film. The EIT-like effect is generated by bright-bright coupling resulting from adjacent ring resonators. High sensitivity up to 1.60 THz/RIU to the environmental refractive index is achieved utilizing the transparency peak. Accompanying with the EIT-like effect, the multi-band slow light phenomenon is obtained around the transparency windows. In addition, by inducing the insulator-metallic transition of the vanadium dioxide layer, the EIT-like curves can be actively manipulated while the multiple modulation is realized without refabricating the structure. Particularly, due to structural symmetry, the EIT-like windows keep unchanged and maintain noticeable with various polarization angles. The proposed structure has potential applications such as terahertz sensors, slow-light devices and modulators.

2-Photon Polymerized IP-Dip 3D Photonic Crystals for Mid IR Spectroscopic Applications

Photonic Crystals (PhC) are periodically structured dielectric materials that have been subject to extensive research efforts over the last two decades. PhC are known for the slow-light phenomenon, which increases the interaction time between light and the target gas, thereby enhancing sensitivity when applied to sensors. Slow light is best realized using three-dimensional (3D) PhC with a complete photonic band-gap (PBG). However, they are inherently difficult to fabricate with planar microfabrication techniques. In this work, we present two-photon polymerized (2PP) stereolithographically fabricated 3D PhC targeting mid-infrared (MIR) spectroscopic range. Finite Element Analysis (FEA) was performed on a two-dimensional (2D) PhC waveguide (PhCW) to analyze the significance of PBG and slow light properties. Additional FEA was conducted and validated experimentally using fabricated 3D PhC. The ability to tune PhC to a desired wavelength along with their repeatability and feasibility is experimentally demonstrated. This letter presents the first, to our knowledge, 3D PhC fabricated using 2PP stereolithography operating at this wavelength.

Exotic light transition between superluminal and subluminal group velocity in a [formula omitted] coupled slab waveguide

We propose a rigorous full-wave modal analysis based on the eigenmodes approach (“supermodes”), that allows the calculation of the transverse electric (TE) and transverse magnetic (TM) stationary propagation eigenmodes in a coupled PT-symmetric slab waveguide. Our findings show that the group velocity, for the fundamental TE0 supermode, passes from superluminal to subluminal speed over both sides of a critical point (CP), located near to the exceptional point (EP). We also demonstrate that the first higher-order supermode, TE1, exhibits a slow light phenomenon around the EP.

Slow-Light Enhanced Liquid and Gas Sensing Using 2-D Photonic Crystal Line Waveguides—A Review

Photonic crystals (PhCs) are periodically structured dielectric materials that have attracted significant research interest in the last two decades for their ability to slow down the group velocity of a propagating pulse envelope with promising sensing applications. This review article discusses the properties of 2-D PhCs including the slow-light phenomenon, bandgap generation, and application of these properties for gas and liquid sensing. Waveguide generation by introducing defects with light guiding and confinement is discussed. In addition, for 2-D PhC line waveguides, a comprehensive review on the slow-light principle and phenomenon of slow-light enhanced sensing for gases and liquids is discussed. 1-D and 3-D PhCs are also reviewed for bandgap generation and defects in PhCs along with present fabrication challenges and future trends. Our study highlights an increase in the detection capabilities of PhC-based sensors paving way for high-sensitivity detectors with applications in ubiquitous monitoring of gases and liquids.

Transparency and Enhancement in Fast and Slow Light in q‐Deformed Optomechanical System

AbstractNonclassical phenomena can be enhanced by introducing q‐deformation in optomechanical systems. This motivates investigation of the optical response in a q‐deformed linearly coupled optomechanical system. The system consists of two deformed cavities that are linearly coupled to the motion of mechanical mirrors, and the cavities are coupled to each other by transmission strength parameter. This study shows that compared to non‐deformed cases, the deformed system exhibits more rapid phase transition at the positions of transparency windows, causing stronger and enhanced fast and slow light phenomena. Moreover, in the region , the optomechanical system results in gain. Additionally, for a fixed deformation of cavities, by tuning the tunneling strength and optomechanical coupling, one can observe a delay and advancement in probe field in the order of milliseconds and even above milliseconds for fine‐tuning of the coupling parameters. Finally, the bridge between mathematical and physical models is built by assuming the deformation to be a primitive root of unity, which indicates a class of anyon models. These results demonstrate that q‐deformation provides a novel method for manipulating and significantly enhancing optical phenomena not only in arbitrarily deformed optomechanical systems but also in anyon models.

All-optical memory based on slow light and Kerr effect in photonic crystal platform with independent write/read/hold control

A general scheme has been proposed for the design of photonic-crystal-based all-optical memory by implementing the Kerr effect and slow light phenomenon and a memory cell with independent control on the read, write and hold processes is presented. A photonic crystal slab platform comprised of air holes in a square array with a hole radius of R = 192.5 nm and slab thickness of 275 nm is considered to realize the optical memory operating at the signal and pump wavelengths of λ = 1550 nm and λ = 1604 nm, respectively. The radii of the holes and the thickness of the proposed slab are engineered to provide proper functionality in the write/read waveguides and memory cell. For the slab thickness of 275 nm, the radii of the defect holes at the center of the read and write channels, and memory cell are determined to be 66 nm, 60.5 nm, and 55 nm, respectively. The pump pulse with a peak power of 2.65 W and a minimum time duration of ∼2.64 ps is required for the reading process. Also, the peak power and minimum time duration of 4.7 W and 1.35 ps, respectively are required to accomplish the writing process. The study has been carried out by 3D PWE and 3D FDTD methods.

Design of Broadband Plasmon‐Induced Transparency Hybrid Metamaterial Based on the Interaction of the Metal and Dielectric Resonances

AbstractIn this paper, a broadband plasmon‐induced transparency (PIT) hybrid metamaterial system (HMS) is realized and numerically demonstrated via the interference between different resonance modes of metal and dielectric resonators. The employed PIT HMS supports a strong near‐fired coupling between unit cells consisting of eight TiO2 nested split rings (dark plasmonic resonators) surrounded by four metal cut wires (bright plasmonic resonators) embedded in the intermediate dielectric layer, and a broad transparency window which is higher than 0.9 is obtained from 0.61 to 0.76 THz with a relative bandwidth of 21.9%. In the transparent window, the drastic change of phase leads to high group delay, and the remarkable slow light phenomenon can be clearly observed. The maximum of the group delay and group index can reach 528 ps and 2880, respectively. The localization distributions of the electromagnetic field intuitively exhibit the generation and action process of destructive interference. The theoretical investigation of the two‐oscillator model further confirms the effectiveness and consistency of the simulation results. In addition, the fourfold symmetric of the proposed PIT HMS supports the liberation from the dependence of incident polarization form. Such an implementation opens a new path for the designing of filtering, switching, and data storing devices.

Study on the PBGs of a two-dimensional photonic crystal with multilayer rings composite structure and its slow light in W1 waveguide

In this paper, we present a scatterer with a multilayer annular nested composite structure. The photonic band gaps (PBGs) characteristics of the two-dimensional photonic crystals and the slow light features of the W1 waveguide are studied by the plane-wave expansion method. The influences of the number and the thicknesses of hollow annular dielectrics on the PBGs are analyzed. Meanwhile, the impact of the refractive index of each dielectric column is also taken into account. Herein, the scatterers are placed in the square and triangular lattices, and the PBGs traits of the TE and the TM modes in different lattice arrangements are fully discussed. With five layers of dielectric, we get a wide range of complete PBGs. When the thickness and refractive index of the dielectric layer are constant, increasing the number of dielectric layers does not always contribute to boosting the PBG scope. With the aggrandizement in the number of dielectric layers, the PBGs of the TM mode are larger and larger, but the PBGs of the TE mode always aggrandize first and then reduce, or even die down. As the thickness of the dielectric layer is altered, the results depict that the PBGs appertain to the TE mode when the thickness is small, while the TM mode and absolute PBGs tend to occur with the condition that the thickness of the dielectric column is large. Besides, the width of the PBGs always aggrandizes to the accession in the refractive index, and when the refractive index adds to a certain value, the PBGs width degrades to the augment in the refractive index. Finally, the slow light phenomenon in the W1 waveguide with a diverse number of ring layers is analyzed by introducing line defects into the structure. In the GaAs waveguide, we obtain group velocities of ±0.23c.

Optical response of a dual membrane active–passive optomechanical cavity

We investigate a dual membrane active–passive cavity where each mechanical membrane individually quadratically coupled to passive and active cavities via two-phonon process. Due to the fact that in the quadratically coupled optomechanical system mean-field approximation fails, hence to analyze the system completely, we switch to a more generalized out of equilibrium approach, namely Keldysh Green’s functional approach. We calculate transmission rate using predetermined full retarded Green’s function, and then numerically examine the effect of the various parameters on the transmission coefficient and discuss the features and physical mechanism behind them in detail. On the basis of the optical responsivity we further extend our study to fast and slow light phenomenon. The results show that our proposed system can not only realize ultra-fast/ultra-slow light under proper choice of cavity parameters but also a realization of the conversion between fast and slow light and vice versa has also been pointed out.

A Tunable Slow Light Device with Multiple Channels Based on Plasmon-Induced Transparency

Slow light devices with buffering capability play a critical role in all-optical signal processing. In this paper, multiple slow light phenomena are implemented based on plasmon-induced transparency (PIT) in our device. The device mainly consists of dual tooth cavities coupled with stub resonators, respectively. Temporal coupled-mode theory model illustrates that the triple PIT phenomena can be achieved based on different formation mechanisms. The simulation results calculated by the finite-difference time-domain method reveal that significant slow light response occurs at two wavelength regions. In addition, the parameters of structure have an important influence on PIT response and slow light characteristics. Moreover, the separate manipulation of wavelength, transmission and group index at transparency peak can be achieved in different slow light channels by adjusting the structural parameters. This plasmonic device is of great significance for the design of optical networks on chips.

Terahertz hybrid metal-graphene metamaterials with tunable dual-band electromagnetically induced transparency

The electromagnetically induced transparency (EIT) effects in metamaterials have been widely studied due to their broad application prospects in the field of optical communications. Previous researchers focused mainly on the regulation of a single EIT effect. Here we proposed a structure containing two pairs of asymmetric C-shaped double-split ring resonators (DSRRs) placed on the two sides of cut wire (CW), and we studied the EIT effect of the structure. Furthermore, in order to tune the EIT peak, two graphene strips are placed on the two pairs of DSRRs. Simulation results show that, the EIT peak can be modulated by adjusting the Fermi level of the graphene strips and the modulation depths as high as 83 % and 87 % can be realized. Besides, slow light phenomenon accompanied by the EIT effect in the structure was investigated. Simulation results implied that, double group delays of 4.4 ps and 3.4 ps can be achieved in the design, and the delays can be adjusted by changing the graphene Fermi level. The physical mechanism of the tunable metamaterial was analyzed in terms of the three-oscillator model.

Slow-light application using dielectrics in a metallic terahertz plasmonic waveguide.

In this paper, a metallic terahertz (THz) plasmonic waveguide comprising subwavelength scale pillars is proposed. The pillars are periodically arranged in one dimension and are assumed to be metallic; on the top of the pillars, dielectric material is deposited. The fundamental guided resonant mode properties of the waveguide are comprehensively examined with and without dielectric material. Furthermore, guided modes are examined while varying the refractive index value (n) of the dielectric material, and it is observed that resonant modes supported by the waveguide strongly depend on n value of dielectrics. The dispersion relations of the guided modes are analyzed to ensure the plasmonic response. To support the numerical results, a Drude model is employed to fit the real and imaginary parts of the complex dielectric function for the proposed waveguide design. The group velocity of the fundamental guided terahertz mode is calculated in order to investigate slow-light properties of the terahertz wave. Additionally, the phase of transmission output and electric field profiles are studied in support of slow-light phenomena. The slow-light phenomenon using a dielectric-metal-based plasmonic waveguide could be very useful in construction of terahertz buffers, storage devices, terahertz sensors, detectors, etc.

Nematic reorientation effects on resonant modes, wavelength mismatch, and slow-light phenomena in one-dimensional magnetophotonic crystals with a dual anisotropic defect.

The present study is devoted to the investigation of spectral properties of an alternated sequence of magnetic and dielectric layers containing a dual defect based on magnetic and nematic layers. Combining the Hydrodynamic Continuum Theory for nematic liquid crystals and Berreman's formalism, we determine how the nematic ordering affects the light localization, polarization rotation, and slow-light phenomena observed in the magnetophotonic system. In particular, we analyze the effects associated with a field-induced reorientation of the director in a nematic defect with strong planar boundary conditions. Our results reveal that field-induced reorientation of the nematic ordering can be used as an efficient mechanism to tune and control the spectral properties of magnetophotonic structure, anomalies in group velocity, and the wavelength mismatch between resonant mode and maximum polarization. The effects of nematic layer thickness are also analyzed.

Maximization of terahertz slow light by tuning the spoof localized surface plasmon induced transparency

This work numerically investigates a localized terahertz (THz) slow light phenomenon by tuning the spoof localized surface plasmon-induced transparency (PIT). A binary meta-molecule supports the interaction of the spoof localized surface plasmon (spoof-LSP), which is composed of a metallic arc and a textured circular cavity of periodic grooves. By tuning the central angle θ of the arc from 90 degrees to 170 degrees, a slow light plateau is found in the transparency window at certain frequency range. A maximum of 46 ps group delay is achieved at the θ of 135. The numerical mapping of the electromagnetic field indicates a new-born dipolar spoof-LSP that appears at the transparency windows on the circular cavity with opposite polarity to the spoof-LSP on the metallic arc. These two spoof-LSPs of opposite direction lead to a fake quadrupole, which will repel each other in magnetic dipole momentum. The slow light achieves maximum with the induced spoof-LSP and is the same as the origin spoof-LSP on the metallic arc in oscillation strength. This work paves a new way for the maximization of THz slow light.

Slow light in a hyperbolic metamaterial waveguide cladded with arbitrary nonlinear dielectric materials

We have demonstrated a hyperbolic metamaterial (HMM) waveguide cladded with arbitrary nonlinear dielectric materials to explore the properties of slow light. The HMM proposed in this paper is assumed as a metal–dielectric stack which can lead to slow light phenomena while being cladded by dielectric materials. Both the asymmetric (i.e., linear–HMM–linear case and nonlinear–HMM–linear case) and symmetric (i.e., linear–HMM–linear case and nonlinear–HMM–nonlinear case) dielectric structures are considered to examine the properties of slow light in the paper. The dispersion relations which are required to investigate the properties of slow light are derived and presented in detail. The results show that the metal filling factor, the dielectric permittivities, and the arbitrary nonlinearity have significantly changed the characteristics of slow light. Parameter dependence of the effects is calculated and discussed.