Showing papers on "Slow light published in 2023"

Producing slow light in warm alkali vapor using electromagnetically induced transparency

Abstract: We present undergraduate-friendly instructions on how to produce light pulses propagating through warm Rubidium vapor with speeds less than 400 m/s, i.e., nearly a million times slower than c. We elucidate the role played by electromagnetically induced transparency (EIT) in producing slow light pulses and discuss how to achieve the required experimental conditions. The optical setup is presented, and details provided for preparation of pump, probe, and reference pulses of the required size, frequency, intensity, temporal width, and polarization purity. EIT-based slow light pulses provide the most widely studied architecture for creating quantum memories. Therefore, the basic concepts presented here are useful for physics and engineering majors who wish to get involved in the development of cutting-edge quantum technologies.

Inverse design of a photonic moiré lattice waveguide towards improved slow light performances.

Abstract: Slow light waveguides in photonic crystals are engineered using a conventional method or a deep learning (DL) method, which is data-intensive and suffers from data inconsistency, and both methods result in overlong computation time with low efficiency. In this paper, we overcome these problems by inversely optimizing the dispersion band of a photonic moiré lattice waveguide using automatic differentiation (AD). The AD framework allows the creation of a definite target band to which a selected band is optimized, and a mean square error (MSE) as an objective function between the selected and the target bands is used to efficiently compute gradients using the autograd backend of the AD library. Using a limited-memory Broyden-Fletcher-Goldfarb-Shanno minimizer algorithm, the optimization converges to the target band, with the lowest MSE value of 9.844×10-7, and a waveguide that produces the exact target band is obtained. The optimized structure supports a slow light mode with a group index of 35.3, a bandwidth of 110 nm, and a normalized-delay-bandwidth-product of 0.805, which is a 140.9% and 178.9% significant improvement if compared to conventional and DL optimization methods, respectively. The waveguide could be utilized in slow light devices for buffering.

Coupling of Photon Emitters in Monolayer WS2 with a Photonic Waveguide Based on Bound States in the Continuum.

Abstract: On-chip light sources are an essential component of scalable photonic integrated circuits (PICs), and coupling between light sources and waveguides has attracted a great deal of attention. Photonic waveguides based on bound states in the continuum (BICs) allow optical confinement in a low-refractive-index waveguide on a high-refractive-index substrate and thus can be employed for constructing PICs. In this work, we experimentally demonstrated that the photoluminescence (PL) from a monolayer of tungsten sulfide (WS2) could be coupled into a BIC waveguide on a lithium-niobate-on-insulator (LNOI) substrate. Using finite-difference time-domain simulations, we numerically obtained a coupling efficiency of ∼2.3% for an in-plane-oriented dipole and a near-zero loss at a wavelength of 620 nm. By breaking through the limits of 2D-material integration with conventional photonic architectures, our work offers a new perspective for light-matter coupling in monolithic PICs.

Gap solitons on an integrated CMOS chip

Abstract: Abstract Nonlinear propagation in periodic media has been studied for decades, yielding demonstrations of numerous phenomena including strong temporal compression and slow light generation. Gap solitons, that propagate at frequencies inside the stopband, have been observed in optical fibres but have been elusive in photonic chips. In this manuscript, we investigate nonlinear pulse propagation in a chip-based nonlinear Bragg grating at frequencies inside the stopband and observe clear, unequivocal signatures of gap soliton propagation, including slow light, intensity-dependent transmission, intensity-dependent temporal delay and gap soliton compression. Our experiments which are performed in an on-chip ultra-silicon-rich nitride (USRN) Bragg grating with picosecond time scales, reveal slow light group velocity reduction to 35%–40% of the speed of light in vacuum, change in the temporal delay of 7 ps at low peak powers between 15.7 W–36.6 W, which is accompanied by up to 2.7× temporal compression of input pulses. Theoretical calculations using the nonlinear coupled mode equations confirm the observations of intensity-dependent temporal delay. Of fundamental importance, this demonstration opens up on-chip platforms for novel experimental studies of gap solitons as the basis of all-optical buffers, delay lines and optical storage.

Nanosensor and slow light based on quintuple Fano resonances in metal-insulator-metal waveguide coupled with concentric-rings resonator

Abstract: In this paper, quintuple Fano resonances are produced and numerically analyzed based on a plasmonic resonator system. The system is composed of an optical metal–insulator–metal (MIM) waveguide, a side-coupled disk, and a concentric-ring resonator. Five Fano resonances can be seen, which originate from the interaction of the cavity mode between the disk resonator and the concentric-ring resonator. The transmission spectrum shows that the Fano resonance can be independently tuned by changing different geometrical parameters, such as the outer radius or inner radius of the concentric-ring resonator. The refractive index sensitivity is 1250nm/RIU for FR5, and the figure of merit is 138.9 (RIU is a refractive index unit). It can also serve as a temperature sensor with a maximum sensitivity of about 0.4nm/ ∘ C. Moreover, for slow light, the maximum delay time is about 0.12 ps at FR3. The proposed nano-scale structure has a sharp Fano line shape and effective ways of tuning independently, which may have applications in slow light and nano-biosensing; for example, we show the application of the detection of different human blood types.

Influence of spontaneously generated coherence on absorption, dispersion, and group index in a five-level cascade atomic system

Abstract: By solving the density matrix equations in the steady state, we have derived analytical expressions for the absorption, dispersion, and group index of a five-level cascade-type atomic system as functions of laser intensity and frequency, spontaneously generated coherence (SGC), and relative phase of applied fields. The influences of SGC and relative phase on absorption, dispersion, and group index of this system under electromagnetically induced transparency (EIT) are studied. It is shown that the three EIT windows of system become deeper and narrower as the strength of SGC increases. These lead to an increase in the slope and the amplitude of the dispersion curves at three EIT windows. As a result, the amplitude of the group index at these three EIT windows also becomes larger when the strength of SGC increases. In particular, the group index can easily be switched between negative and positive values i.e., the light propagation can easily be converted between superluminal to subluminal modes by adjusting the strength of SGC, relative phase or the coupling laser intensity.

Electromagnetically induced transparency based on metal-graphene hybrid metamaterials

Abstract: Abstract This paper introduces a novel metal-graphene composite metamaterial modulator that can produce a tunable EIT (Electromagnetically induced transparency) effect with good modulation effect under the action of an applied voltage. The material structure consists of bright mode coupling between a metal strip and a metal U-shaped ring. We investigated the nature of the field and indicated that the detuning of the dipole of the metallic ribbon structure and the quadrupole structure of the metallic U-ring induces an EIT-like reaction. The coupling effect of the metal resonant cavity was analyzed, this is, the coupling between the metal layer and the mono-graphene on the transparency window. By varying the voltage between the substrate silicon and the monolayer graphene surface in the structure, the modulator can achieve a maximum modulation depth of 83.4% and on the transparent window, the light will have a positive group delay of 8 ps, This wok can be applied to future 6G wireless communications et al.

Generating structured 3D linear space-time light bullets with nonlocal nanophotonics

Abstract: We propose the generation of 3D linear light bullets propagating in free space using a single passive optical surface. The device is a single-layer photonic crystal slab. It can automatically transform an incident conventional Gaussian pulse into a light bullet in the reflection. Our approach also provides simultaneous control of various properties including group velocity, spin, and orbital angular momentum. Our results may advance practical applications of light bullet.

Controllable magnon-induced transparency in a ferromagnetic material via cross- and self-Kerr effects

Abstract: Nonlinear interactions between optical fields and magnetic modes in cavity magnonics constitute a rich source of various nontrivial effects in optics and quantum information processing. In cavity magnonics, the nonlinear cross-Kerr effect, which shifts the cavity's central frequency when a magnetic material is pumped, causes the system to exhibit both Kittle and magnetostatic modes. Here, we propose a new scheme for the investigation of probe fields transmission profiles in cavity magnonic systems composed of a microwave cavity and a ferromagnetic material (Yttrium iron garnet sphere). We report single-to-double magnon-induced transparency (MIT) dips and a sharp magnon-induced absorption (MIA) peak, and demonstrate how nonlinear cross- and self-Kerr interactions can significantly enhance or suppress these phenomena. It is observed that the splitting of the MIT window occurs when we incorporate magnon-magnon modes coupling, which helps introducing a new degree of freedom to light-matter interaction problems. Moreover, we investigate the propagation of group delay in the vicinity of transparency and demonstrate how a sharp dip allows the realization of slow light for a longer period of time. We found that both the cavity-Kittle and magnon-magnon modes coupling parameters influence the propagation of group delay, which demonstrates how subluminal-to-superluminal (and vice versa) propagation phenomena may occur and transform. These findings could pave the way for future research into nonlinear effects with novel applications in cavity magnonics devices, which might be exploited for several applications such as quantum computing devices and quantum memories.

Systematic design of a robust half-W1 photonic crystal waveguide for interfacing slow light and trapped cold atoms

Abstract: Novel platforms interfacing trapped cold atoms and guided light in nanoscale waveguides are a promising route to achieve a regime of strong coupling between light and atoms in single pass, with applications to quantum non-linear optics and quantum simulation. A strong challenge for the experimental development of this emerging waveguide-QED field of research is to combine facilitated optical access for atom transport, atom trapping via guided modes and robustness to inherent nanofabrication imperfections. In this endeavor, here we propose to interface Rubidium atoms with a photonic crystal waveguide based on a large-index GaInP slab. With a specifically tailored half-W1 design, we show that a large coupling to the waveguide can be obtained and guided modes can be used to form two-color dipole traps for atoms at about 100 nm from the edge of the structure. This optimized device should greatly improve the level of experimental control and facilitate the atom integration.

Photothermally-Induced Nonlinearity in a Quantum Multimode Optical System

Abstract: Similar to radiation pressure, photothermal effects connect the optical path length to an intracavity field, resulting in nonlinear behavior of the resonator due to thermal effects. Here, we theoretically investigate the nonlinear optics that emerge as a result of photothermal effects in a multimode optical system composed of two cavity modes coupled via hopping coefficient and with two mechanical modes through coupling rates. We report single to double photothermally-induced transparency (PTIT) dips, and a single sharp photothermally-induced absorption (PTIA) peak, and demonstrate that photothermal and strong coupling coefficients can suppress this phenomenon. Moreover, we observe Fano resonances in the absorption profile by monitoring probe transmission in the off-resonant configuration of the transparency phenomenon. The dynamics of group delay or advance are investigated in the range of transparency such that a sharp dip can assist in achieving slow light for a longer time. Using appropriate experimental parameters, our proposed work can pave the way for future practical applications in quantum information processing based on multimode interactions.

Tunable magnomechanically induced transparency and fast-slow light in a hybrid cavity magnomechanical system

Abstract: We theoretically explore the tunability of magnomechanically induced transparency (MMIT) phenomenon and fast-slow light effect in a hybrid cavity magnomechanical system in which a high-quality yttrium iron garnet (YIG) sphere and an atomic ensemble are placed inside a microwave cavity. In the probe output spectrum, we can observe magnon-induced transparency (MIT) and MMIT due to the photon-magnon and phonon-magnon couplings. We further investigate the effect of atomic ensemble on the absorption spectrum. The results show that better transparency can be obtained by choosing appropriate atomic ensemble parameters. We give an explicit explanation for the mechanism of the phenomenon of Fano resonance. Besides, we also discuss the phenomena of slow-light propagation. The maximum group delay increases significantly with the increase of the atom-cavity coupling strength, and the conversion between slow light and fast light can also be achieved by adjusting the atom-cavity coupling strength. These results may have a potential application for quantum information processing and high precision measurement.

Slow light by dual-periodic self-similar dielectric multilayered films.

Abstract: We demonstrate the emergence of slow-light in dual-periodic dielectric one-dimensional photonic crystals with self-similar features at different length scales. Specifically, using numerical modelling, we explore self-similar photonic crystals which are formed as effective combinations of dual periodic stacks of dielectric layers and show that the emergent photonic band diagram can be widely designed by different structural parameters. The width and the position of bandgaps can be designed to work over a wide range of bands and frequencies. The proposed design also leads to the emergence of flat bands and major slow-light regimes, with possible group refractive index of light as large as 103 and in a range of bands.

Tunable terahertz double plasmon induced-transparency based on monolayer patterned graphene structure

Abstract: In this paper, tunable double plasmon-induced transparency (PIT) is achieved in a monolayer-patterned graphene structure. The proposed structure is composed of a middle graphene-strip and two π-shape graphene microstructures. Results show that the double PIT effect is originated from the destructive interference between two bright modes and one dark mode, a equivalent coupled mode theory (CMT) model is utilized to confirm the finite-difference-time-domain (FDTD) simulation. The influences of the chemical potential, scattering rate, and geometrical size on the double PIT transmission spectrum are investigated. The modulation properties of the proposed structure have been studied in detail and it shows excellent modulation depth (MD) and relatively low insertion loss (IL). Moreover, the proposed structure shows a maximum refractive index sensitivity about2.38THz/RIU, and the maximum figure of merit (FOM) can reach 43.4. The effect of the refractive index of the substrate on the sensing performance is also investigated. Thus, the proposed structure can be applied in the areas of multi-function optical switches, terahertz slow light devices, modulators, and sensors.

Size effect on light propagation modulation near band edges in one-dimensional periodic structures

Abstract: Periodic photonic structures can provide rich modulation in propagation of light due to well-defined band structures. Especially near band edges, light localization and the effect of near-zero refractive index have attracted wide attention. However, the practically fabricated structures can only have finite size, i.e., limited numbers of periods, leading to changes of the light propagation modulation compared with infinite structures. Here, we study the size effect on light localization and near-zero refractive-index propagation near band edges in one-dimensional periodic structures. Near edges of the band gap, as the structureʼs size shrinks, the broadening of the band gap and the weakening of the light localization are discovered. When the size is small, an added layer on the surface will perform large modulation in the group velocity. Near the degenerate point with Dirac-like dispersion, the zero-refractive-index effects like the zero-phase difference and near-unity transmittance retain as the size changes, while absolute group velocity fluctuates when the size shrinks.

Controllable magnon-induced transparency in a ferromagnetic material via cross- and self-Kerr effects

Abstract: Nonlinear interactions between optical fields and magnetic modes in cavity magnonics constitute a rich source of various nontrivial effects in optics and quantum information processing. In cavity magnonics, the nonlinear cross-Kerr effect, which shifts the cavity's central frequency when a magnetic material is pumped, causes the system to exhibit both Kittle and magnetostatic modes. Here, we propose a new scheme for the investigation of probe fields transmission profiles in cavity magnonic systems composed of a microwave cavity and a ferromagnetic material (Yttrium iron garnet sphere). We report single-to-double magnon-induced transparency (MIT) dips and a sharp magnon-induced absorption (MIA) peak, and demonstrate how nonlinear cross- and self-Kerr interactions can significantly enhance or suppress these phenomena. It is observed that the splitting of the MIT window occurs when we incorporate magnon-magnon modes coupling, which helps introducing a new degree of freedom to light-matter interaction problems. Moreover, we investigate the propagation of group delay in the vicinity of transparency and demonstrate how a sharp dip allows the realization of slow light for a longer period of time. We found that both the cavity-Kittle and magnon-magnon modes coupling parameters influence the propagation of group delay, which demonstrates how subluminal-to-superluminal (and vice versa) propagation phenomena may occur and transform. These findings could pave the way for future research into nonlinear effects with novel applications in cavity magnonics devices, which might be exploited for several applications such as quantum computing devices and quantum memories.

Highly confined low-loss light transmission in linear array-enabled hybrid plasmonic waveguides

Abstract: Deep subwavelength highly confined and long-range optical propagation is vital for photonics integration. However, the performance of the guided mode could be improved by the trade-off between light confinement and loss. Here, we demonstrate a high-performance hybrid waveguide consisting of a high-index nanowire separated from a linear array by a low-index dielectric gap. The array significantly achieves the plasmonic platform optimization based on a linear combination of few-layer graphene (FLG) and hexagonal boron nitride (hBN) layers. Through the hybridization of graphene plasmon polaritons and hyperbolic phonon polaritons mode, the resulting hybrid waveguide shows at least double times larger propagation distance and smaller mode area than the multilayer waveguide. Further, modulated by altering material configuration and geometric effects, the mode properties reveal that it is more flexible to adjust the optical transmission, along with a strong deep-subwavelength mode with low loss. Because of highly confined low-loss propagation, the hybrid waveguide is expected to be an excellent building block for various mid-infrared photonic integrated circuits. The present structure also has the potential to be extended to other FLGs, like magic-angle twisted bilayer graphene and trilayer graphene/hBN moiré superlattice.

Large group delay and low loss optical delay line based on chirped waveguide Bragg gratings.

Abstract: On-chip optical delay lines (ODLs) based on chirped waveguide Bragg gratings (CWBG) have attracted much attention in recent years. Although CWBGs are well developed, the CWBG which have large group delay (GD), large delay-bandwidth product and low loss while is circulator-free have little been investigated so far. In this work, we propose and experimentally demonstrate such a CWBG-based ODL. This device is fabricated on a low-loss 800-nm-height silicon nitride platform, combining 20.11-cm long index-chirped multi-mode spiral waveguide antisymmetric Bragg gratings with a directional coupler. The bandwidth of this circulator-free ODL is 23 nm. The total GD is 2864 ps and the delay-bandwidth product is 65.87 ns·nm, which both are the largest values achieved by on-chip CWBG reported to our knowledge. Its loss is 1.57 dB/ns and the total insertion loss of the device is 6 dB at the central wavelength near 1550 nm. This integrated CWBG can be explored in practical applications including microwave photonics, temporal optics, and optical communication.

Dispersion Management of Light Pulse Transparency in Quantum Metamaterials

Abstract: We present a theoretical prediction of a novel, nonEIT, mechanism for the achievement of a transparency window. It relies on an intrinsically nonlinear (soliton type) mechanism which may be exploited for the production of slow light, which may appear in a photonic band-gap structure: the infinite coupled cavity array (CCA), filled with two-level systems - qubits. Each cavity contains a single qubit. The most important prediction is substantial dependence of the pulse transparency on its width. In particular, the medium is opaque for very short pulses with carrier wave frequency below the photonic gap. When the pulse width exceeds the critical one, a twin transparency window separated by a finite band gap appears in the SIT pulse dispersion law. Both low-frequency TW and the SIT pulse band gap lie entirely within the polaritonic band gap.

A Novel Approach for Achieving Slow Light With Ultra-Low Dispersion in Plasmonic Device

Abstract: Compact slow light devices are essential components for performing data caching and signal processing in photonic integrated loops. In this paper, an integrated ultra-low-dispersion slow light device with a novel method is proposed. The device consists of three parts (hexagonal resonator with elliptical core, stub cavity, and tooth cavities) coupled to the waveguide, respectively. Dual Fano resonances occur in the structure, and transmission characteristics of the structure are investigated in detail by temporal coupled-mode theory. Finite-difference time-domain simulations reveal that the transmission bandwidth, group index, and delay time can be manipulated by adjusting the separation between two Fano resonances, which is related to the eccentricity of the oval core. At the 850.7 nm window, transmission bandwidth and average group index are optimized to 21.1 nm and 12.19, respectively. Moreover, multiple dispersionless wavelengths within the slow light bandwidth are obtained based on dual Fano resonances. Furthermore, feasibility of the device to perform slow light function in different channels is researched, and device performance is presented and analyzed. This device has a great impact on improving the quality of signals on chips, and the method introduced is of great significance for designing other photonic devices.

Normal and anomalous dispersion study on probe light propagation in the presence of structured coupling light using electromagnetically induced transparency protocol

Abstract: Here, we present a study on the dispersion features obtained in an electromagnetically induced transparency (EIT) experiment using a three-level cascade configuration in an 87Rb atomic vapor medium in the presence of Laguerre–Gaussian (LG) light as a coupling. A doublet transmission structure was obtained experimentally, and dispersion spectra were extracted using transmission spectra to study the probe light behavior. Dispersive regions that exhibit normal and anomalous nature were studied considering the polarization of various orientations as a coupling light. We established that normal dispersive region shows steep positive slopes, and anomalous dispersive region shows negative slopes, which can be controlled by polarization orientations. Owing to the change in the slopes of dispersion, normal and anomalous dispersive region is observed, and spectrum shows the effects of subluminal and superluminal propagation of probe light. This work, to the best of our knowledge, is novel in the study of dispersive region arising out of double-resonance EIT transmission spectra in the presence of LG light with the l=10 and p=0 mode as a coupling light with various polarization orientations. In the discussion, we establish that single parameter θ is sufficient for identifying the orientation and ellipticity of the polarization ellipse and also determine that the polarization of coupling light acts as a tuning parameter for changing the behavior of normal and anomalous dispersive region. Slow and fast light or superluminal propagation of probe light arise as a consequence of positive or negative group index, and fast light does not violate the principle of causality. Slow and fast light have future applications in high-speed quantum information and quantum communication using EIT-based protocol.

Light drag in an optically dense left-handed atomic medium

Abstract: In this paper, we investigate the light drag in an optically dense negative refractive index medium. Our model is a four-level atomic system in which we demonstrate an enhancement of the light drag while keeping the negative refraction condition. Furthermore, we control the shift in the light drag by tuning both the strong coupling field and the detuning. Hence, we observe that the light drag in the negative refractive index material can be controlled to switch from subluminal to superluminal at various ranges of the detuning. Our system suggests a straightforward technique for realizing and controlling light dragging in materials with negative refractive indices, or ‘NRI,’ which might open the way for more efficient use of left-handedness in atomic systems.

Design and simulation of high modulation efficiency, low group velocity dispersion lithium niobate slow-wave electro-optic modulator based on a fishbone-like grating

Abstract: • In this paper, we propose an on-chip slow-wave electro-optic modulator with improved modulation efficiency on lithium-niobate-on-insulator platform. • The slow-light effect is realized with flat optical operating bandwidth, near zero group velocity dispersion, and low loss. • A matched micro-structure electrode is designed to realize the low group velocity of the microwave modulation signal. Thin-film lithium niobate (LN) has emerged as an excellent platform for electro-optic modulators (EOMs) owing to its strong electro-optic (Pockels) effect. However, it remains an open challenge to achieve high modulation efficiency in chip-scale EOMs, primarily due to the limitation of light-matter interaction. Here, we propose an on-chip slow-wave LN EOM with a length of 3.4 mm with high modulation efficiency by using a fishbone-like grating. By assembling the fishbone-like grating, the Pockels effect is significantly enhanced as a result of the compression of the local density of states. Benefiting from this effect, the modulation efficiency of the modulator can be improved to 4.6 times of the original. In addition, a 3 mm matched micro-structure electrode is designed to realize the low group velocity of the microwave modulation signal. The simulation results show that the modulation efficiency of this slow-wave EOM is 1.42 V·cm. The slow-light effect is realized theoretically with a flat optical operating bandwidth of about 21 nm, group velocity dispersion < 2 ps 2 /mm, and low loss < 0.33 dB. Additionally, a 3 dB modulation bandwidth of 80 GHz is verified by simulation by virtue of the proposed micro-structure electrode.

Light gap bullets in defocusing media with optical lattices

Abstract: Searching for three-dimensional spatiotemporal solitons (also known as light/optical bullets) has recently attracted keen theoretical and experimental interests in nonlinear physics. Currently, optical lattices of diverse kinds have been introduced to the stabilization of light bullets, while the investigation for the light bullets of gap type -- nonlinear localized modes within the finite gap of the underlying linear Bloch spectrum -- is lacking. Herein, we address the formation and stabilization properties of such light gap bullets in periodic media with defocusing nonlinearity, theoretically and in numerical ways. The periodic media are based on two-dimensional periodic standing waves created in a coherent three-level atomic system which is driven to the regime of electromagnetically induced transparency, which in principle can also be replaced by photonic crystals in optics or optical lattices in ground-state ultracold atoms system. The temporal dispersion term is tuned to normal (positive) group velocity dispersion so that to launch the light gap bullets under self-repulsive nonlinearity; two types of such light gap bullets constructed as 3D gap solitons and vortices with topological charge m=1 within the first finite gap are reported and found to be robustly stable in the existence domains. On account of the light bullets were previously limited to the semi-infinite gap of periodic media and continuous nonlinear physical systems, the light gap bullets reported here thus supplement the missing type of three-dimensional spatiotemporal localized modes in periodic media which exhibit finite band gaps.

Auxiliary-Cavity-Assisted Slow and Fast Light in a Photonic Molecule Spinning Optomechanical System

Abstract: We investigate the coherent optical propagation in a photonic molecule spinning optomechanical system consisting of two whispering gallery microcavities in which one of the optical cavities is a spinning optomechanical cavity and the other one is an ordinary auxiliary optical cavity. As the optomechanical cavity is spinning along the clockwise or counterclockwise direction, the cavity field can undergo different Sagnac effects, which accompanies the auxiliary optical cavity, together influencing the process of the evolution of optomechanically induced transparency and its related propagation properties, such as fast and slow light effects. The numerical results indicate that the enhanced slow and fast light and the conversion from fast to slow light (or slow to fast light) are determined by the spinning direction of the optomechanical cavity and the coupling of the two optical cavities. The study affords further insight into the photonic molecule spinning optomechanical systems and also indicates promising applications in quantum information processing.

Slow-Light and Sensing Performance Analysis Based on Plasmon-Induced Transparency in Terahertz Graphene Metasurface

Abstract: In this article, a polarization-independent graphene metasurface structure is designed to realize the excellent functions of slow-light and sensing generated based on plasmon-induced transparency (PIT) in terahertz (THz) region. The structure includes a cross-shaped and four square graphene resonators that are identical. The unique PIT transparent window generated by bright–bright mode coupling is studied by using finite difference time domain (FDTD) and coupled mode theory (CMT), which are highly consistent. By changing the Fermi level and carrier mobility of graphene, the transmission spectrum of PIT can be tuned effectively. Interestingly, due to the field enhancement and strong dispersion properties of surface plasma, the graphene metasurface proposed in this article has excellent effects in slow-light, and the maximum group index can reach 658. At the same time, because the transmission spectrum of PIT is sensitive to the external refractive index, the sensitivity and figure of merit (FOM) used to evaluate the sensing performance of the structure are 1.7134 THz/RIU and 144.45, respectively. Finally, because the graphene metasurface is a center symmetric structure, it has polarization-insensitive performance. The proposed structure can be used as a slow-light device or applied to biomolecular recognition, environmental monitoring, and other THz sensing fields.