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A novel planar monolayer graphene metamaterial structure containing rectangular interrupted graphene is proposed. Dynamically tunable multiple plasmon‐induced transparency (PIT) and slow light are obtained within the terahertz band through destructive interference between continuous dark and interrupted bright modes. Two distinct graphene types function as the optical dark and bright modes, and continuous graphene array is the nonradiative dark mode, whereas interrupted graphene array is the broad linewidth bright mode, respectively. Given the existence of graphene structure in the continuous state, continuous graphene Fermi level is dynamic tuned through the simple use of the bias voltage. Expressions of n‐order coupled mode theory (CMT) are correctly deduced, with CMT fitting theoretical analysis being identical to finite‐difference time‐domain numerical simulation based on dual‐ and triple‐PIT results for n = 3 and n = 4 cases, respectively. The continuous graphene Fermi level increases within 0.7–1.1 eV; the group index of the dual‐PIT system is maintained within 475.1–801.6, while that of the triple‐PIT system is 583.3–886.3. Additionally, the maximal group index is as high as 886.3 at 1.1 eV, indicating that an outstanding slow light device is established. Consequently, these proposed structures and research outcomes can guide the design of multichannel optical filters, excellent slow light devices, and dynamically tunable optical modulators. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the phenomenon of optomechanically induced transparency (OMIT) in a cavity that has a moving end mirror and is subjected to an external force. Furthermore, we place an optical parametric amplifier (OPA) inside the cavity. We show that the transmission intensity of the probe field and the group delay is enhanced by the parametric gain and phase of the OPA. We also show that this enhancement is influenced by external forces. We believe that these findings could be valuable in the area of quantum information processing. [ABSTRACT FROM AUTHOR]

In this study, we explore the effect of integrated auxiliary rods at varying angles to the primary cavity rod on the dispersion characteristics of the photonic crystal coupled cavity waveguide (PC CCW). Here, it is intended to break the symmetry of the cavity region by introducing auxiliary rods which gives the degree of freedom for tuning effective index of the PC waveguide. Furthermore, rotational angle variations of auxiliary rods reveal slow light operation of the PC CCW where the group index is maximized and group velocity dispersion, as well as the third-order dispersion, are minimized. In addition, auxiliary rods with a broken symmetry increase not only group index but also operating bandwidth and accordingly increase group bandwidth product by 675%. Leveraging these results, we demonstrate effective rainbow trapping by manipulating the auxiliary rod angles in photonic crystal coupled cavity waveguides. Our results have encouraging implications for optical buffering, multiplexing, demultiplexing, advanced time-domain and spatial signal processing. [ABSTRACT FROM AUTHOR]

We theoretically propose a loop-coupled multimode optomechanical system (OMS) with a single-mode cavity, a two-level system (TLS), and a mechanical resonator, which are coupled to each other. With controlled coupling parameters, the loop-coupled multimode OMS can flexibly transform into different OMSs (e.g. cavity OMSs, cavity quantum electrodynamic systems). By simultaneously driving the single-mode cavity using pump and probe fields, we investigate the coherent optical response and transmission spectra for the transparent window and absorption dips. Additionally, the transparent window and absorption dips that induce coherent light propagation were demonstrated. Our findings demonstrate that the transparent window and absorption dips can generate slow (fast) light, and that the control of coupling parameters can modulate optical fields in different OMSs. With further weaving of these coupling parameters, the loop-coupled multimode OMS can be a quantum information processing platform for chip-scale applications. [ABSTRACT FROM AUTHOR]

This study investigates the possibility of achieving a slow signal field at the level of single photons inside nanofibers by exploiting stimulated Brillouin scattering, which involves a strong pump field and the vibrational modes of the waveguide. The slow signal is significantly amplified for a pump field, with a frequency higher than that of the signal and attenuated for a lower pump frequency.We introduce a configuration for obtaining a propagating slow signal without gain or loss and with a relatively wide bandwidth. This process involves two strong pump fields with frequencies both higher and lower than that of the signal where the effects of signal amplification and attenuation compensate each other. We account for thermal fluctuations due to the scattering of thermal phonons and identify conditions under which thermal contributions to the signal field are negligible. The slowing of light through Brillouin optomechanics may serve as a vital tool for optical quantum information processing and quantum communications within nanophotonic structures. [ABSTRACT FROM AUTHOR]

A novel plasmonic structure is proposed to achieve plasmon-induced transparency (PIT), which is composed of a stub resonator (SR) and a square ring resonator (SRR). The research delves into the theoretical calculations and numerical simulations to explore the formation and evolution mechanisms of PIT. In this innovative structure, the evolution of PIT is notably influenced by geometric parameters, and its sensing performance in various environments is thoroughly examined. Furthermore, the study evaluates its potential applications in the domains of slow light and optical switches. Moreover, the introduction of an additional SR and SRR to the original structure leads to a multi-PIT phenomenon, and the underlying reasons for this phenomenon are elucidated. Meanwhile, the sensor sensitivity in air, alcohol, and glucose media is calculated to be improved by 12.5%, 12.7%, and 9.1%, respectively, compared with the previous work. This hybrid structure effectively enhances the overall performance of the plasmonic system in practical applications. Consequently, this proposed plasmonic structure introduces a fresh perspective for the development of multifunctional nanoscale optical devices, particularly in the realms of nanosensors, slow light technologies, optical storage, and optical switches. [ABSTRACT FROM AUTHOR]

We explore novel optomechanically induced transparency (OMIT) and prolonged slow light in a linear and quadratic optomechanical system (OMS) with the Coulomb coupling. The hybrid OMS includes a Fabry–Pérot cavity and two charged mechanical resonators (MR1 inside the cavity and MR2 outside the cavity), where the interaction between the charged MR1 and the cavity field are both linear and quadratic in the MR1's displacement, and the charged MR1 and the charged MR2 mutually coupled via Coulomb interaction. Specifically, the transmission of the output field exhibits three transparency window dips. The Coulomb coupling strength is responsible for creating two transparency window dips near δ / ω m = 1 , which results from the mechanical dressed mode. Simultaneously, the quadratic coupling between the charged MR1 and the optical cavity field significantly contributes to another transparency window dip near δ / ω m = 2 , which is attributed to the two-phonon process. In addition, by adjusting the value of Coulomb coupling strength, linear (quadratic) coupling and frequency of the two mechanical resonators, one can attain prolonged slow light with a group delay extending to tens of milliseconds. Furthermore, the positive (negative) value of quadratic coupling strength can determine the switching behavior of the group delay (i.e., from superluminal to subluminal propagation) on the right (left) side of δ / ω m = 2 . We believe that the results have potential applications in manipulating the performance of OMIT devices and optical switching. [ABSTRACT FROM AUTHOR]

By employing the density matrix approach, this study systematically examines the impact of a longitudinal magnetic field on electromagnetically induced transparency (EIT) within the context of the effective three-level Zeeman sublevels associated with the $ {D_2} $ D 2 -line of 87Rb atomic vapor. Our investigation reveals that a sufficient enhancement in the longitudinal magnetic field induces a discernible narrowing of the EIT linewidth, accompanied by an enhancement in the peak transmission through a Rubidium (Rb) vapor cell. Related to these, we analyse the effect of magnetic field on the dispersive properties of the system, including group delay and group velocity and observed a slight decrement in the group delay and increment in the group velocity, which specifies the transition from slow to fast light under the application of the magnetic field. [ABSTRACT FROM AUTHOR]

In this paper, we propose a tunable metal-graphene hybrid metamaterial modulator based on the electromagnetically induced transparency (EIT) effect, which can be applied in the terahertz modulation field. The device consists of a U-shaped sliver strip and a rectangular sliver ring. The proposed structure is coupled by bright-bright EIT mode to generate a narrow-band electromagnetically induced transparent window. In the modulation process, the transparent window only changes in amplitude, keeping the resonant frequency constant and improving the device's resistance to interference. Active tunability is achieved by adjusting the bias voltage to alter the Fermi level of the graphene film layer, thereby facilitating modulation performance adjustment. The transparent window has a narrow bandwidth of 0.053 THz, with the transparent peak located at 0.773 THz. The maximum modulation depth of the proposed device is 74.1% and the maximum positive group delay in the transparent window can reach 0.01 ns. The designed structure has the advantages of terahertz modulation and slow light field due to its narrow-band tunability. This work provides a potential solution for electromagnetic wave control for 6G wireless communication. [ABSTRACT FROM AUTHOR]

In this paper, by finite-difference-time-domain (FDTD) simulation, we numerically demonstrate a plasmon-induced transparency (PIT) effect based on a carbon nanotubes (CNT) metamaterial. The proposed CNT metamaterials are regular arrays of unit cells composed of a cut wire and two rectangular split ring resonators (RSRRs). Under the excitation of a TM-polarization terahertz wave, a single PIT transparency window is achieved for the symmetry CNT metamaterial. By breaking the symmetry of the proposed structure with different sizes of RSRRs, a double PIT window is realized. Results show that the PIT effect is originated from the destructive interference of the three bright modes. A coupled harmonic oscillator model is used to describe the destructive interference between the three bright modes, and the results agree well with the FDTD simulation. The effect of geometrical sizes, like coupling distance, splitting size, and opening direction between two RSRRS on the PIT window is analyzed in detail. Further, the slow light performance of the proposed asymmetric CNT metamaterial is investigated, and a maximum time delay of 1.71 ps is obtained. Finally, an extensive sensitivity of 1.12 THz/RIU is obtained. Therefore, the proposed CNT-based device exhibits numerous potential applications in THz slow light, sensors, and modulators. [ABSTRACT FROM AUTHOR]

In this paper, we present a single nano ring resonator using Annular Photonic Crystal (APC) with ultra-compact size for applications in versatile optical network components. The proposed resonator is designed in the hexagonal lattice, made up of Silicon (Si) planar and annular rods, where the annular rods are filled with Silicon Nitride (Si3N4). Despite being pervasive, the proposed structure operates mostly in the C-band wavelength, providing high resonation, low insertion loss, high contrast ratio, and large bandwidth with low loss comprising a single resonator ring with photonic crystal waveguides. This structure is used to realize several high-performance optical network devices like optical ring resonator, 4 × 2 reversible encoder, 1 × 2 power splitter, and a multiplexer. Several parameters and their performances are optimized for this miniaturized photonic device using Finite Difference Time Domain (FDTD) method. This device works in the quantum regime as a slow light device with a better squeeze factor enabling quantum computing. The proposed nanostructure, having a Quality factor (Q) of 396.05, is highly suitable for optical network applications. [ABSTRACT FROM AUTHOR]

Multiwavelength nanophotonic devices are essential components in photonic integrated circuits for on-chip all-optical signal processing applications with enhanced data-storage capacity and increased bandwidth. Wavelength demultiplexing is a widely used photonic processing function, required for photonic signal processing on compact silicon chip designs. In this paper, we study optical rainbow trapping in a line defect photonic waveguide, and propose to use that effect for demultiplexing the light at visible spectrum. A defect waveguide is created in graded-index photonic crystal (GRIN PC) structure (the structure is composed of Si- PC cylinders having gradually varying radii along one dimension) as main channel, which allows the rainbow-trapping along the waveguiding channel. Vertical (side) channels are introduced to the system for efficient wavelength demultiplexing with low crosstalks and high coupling efficiencies thanks to the fact that incident light is localized at different positions along the main channel for certain operating visible wavelengths of The corresponding inter-channel cross-talks of is obtained at these incident wavelengths, which strengthens the idea of using such a GRIN PC structure for efficient wavelength demultiplexing applications. The studied multichannel demultiplexing device is relatively compact with a footprint of , which could be fabricated via simple lithography processes on a single Si- wafer. As far as authors' knowledge, this is the first time in literature that GRIN PC waveguide is implemented for multichannel wavelength demultiplexing function. The proposed GRIN PC design could be implemented for color sensitive photo-detection, absorption enhancement and optical spectroscopy. [ABSTRACT FROM AUTHOR]

The bandwidth limitation of slow light may distort optical pulses, potentially affecting their practical application. Therefore, researching structures capable of overcoming this limitation could represent a valuable step forward. This theoretical work explores a 2D photonic crystal waveguide with high bandwidth. The optimized structure, comprised of Ge cylinders in an air background, is designed to be arranged in square lattices containing a line defect. The line defect consists of a series of half-cylinders, with their centers aligned with neighboring cylinders at half the lattice constant. This defect generates a waveguide mode that propagates along the line. Additionally, the group index and bandwidth of the mode were studied and optimized for different radii of the photonic crystal. With this relatively simple structure and the selection of appropriate geometric sizes, high bandwidth and a group-index-bandwidth-product of up to one could be achieved. [ABSTRACT FROM AUTHOR]

This study investigates the possibility of achieving a slow signal field at the level of single photons inside nanofibers by exploiting stimulated Brillouin scattering, which involves a strong pump field and the vibrational modes of the waveguide. The slow signal is significantly amplified for a pump field, with a frequency higher than that of the signal and attenuated for a lower pump frequency. We introduce a configuration for obtaining a propagating slow signal without gain or loss and with a relatively wide bandwidth. This process involves two strong pump fields with frequencies both higher and lower than that of the signal where the effects of signal amplification and attenuation compensate each other. We account for thermal fluctuations due to the scattering of thermal phonons and identify conditions under which thermal contributions to the signal field are negligible. The slowing of light through Brillouin optomechanics may serve as a vital tool for optical quantum information processing and quantum communications within nanophotonic structures.

AbstractWe propose a novel acousto-optic (AO) devise using suspended fishbone nanobeams based on phononic and photonic potential well (PnPW and PtPW). We aim to reduce the traditional device size and eliminate the need for mirror regions in 1-D nanobeam cavity. By manipulating the frequencies of slow sound (SS) and slow light (SL) modes through geometric parameters, we can create potential wells for phonons and photons. The potential wells concentrate the waves inside the resonant cavity simultaneously, leading to an increase in AO coupling rate. We demonstrate the capability of potential wells in improving the AO coupling rate and investigate the impact of both wells. Some distribution of the phonons may affect the photons with a negative contribution, leading to a decrease in the coupling rate. Careful selection of appropriate acoustic and optical modes can overcome this limitation, making this structure a promising candidate for designing AO devices in silicon photonics.

In this paper, slow light features of an engineered photonic crystal waveguide are presented. The combined effect of lattice shift, lattice twist and introduction of ring-like holes (rings) in the innermost rows on the slow light features is studied. The rings are introduced in the first and second innermost rows of the waveguide. Slow light is characterized by calculating group index, second and fourth-order dispersions, and delay-bandwidth products. MIT Photonic Bands software is used for simulation. With rings in the innermost rows, a flat band of 17.71 nm is observed with a group index value of 12.72 and a flat band of 40.16 nm with a group index of 7.77. The normalized delay bandwidth product (NDBP) is observed as 0.1378 in the first structure and 0.1874 in the second structure with the proposed effects. These values are nearly 4.3 times higher in comparison with the NDBP value of the base structure (0.0436) and approximately 2 times higher than the engineered structure (0.0927). These structures are useful in slow light applications. [ABSTRACT FROM AUTHOR]

Here, we study the controllable optical responses in a two-cavity optomechanical system, especially on the perfect optomechanically induced transparency (OMIT) in the model which has never been studied before. The results show that the perfect OMIT can still occur even with a large mechanical damping rate, and at the perfect transparency window the long-lived slow light can be achieved. In addition, we find that the conversion between the perfect OMIT and optomechanically induced absorption can be easily achieved just by adjusting the driving field strength of the second cavity. We believe that the results can be used to control optical transmission in modern optical networks. [ABSTRACT FROM AUTHOR]

Theoretically, we aim to optimize the parameters related to slow light in a 2D heterostructure photonic crystal. Two types of heterostructures were investigated by joining two photonic crystals: one composed of square holes and the other with circular rods or vice versa. The plane wave expansion and supercell method are used to analyze the waveguide mode. Germanium is assumed to be the material for the rods and background. The group index and bandwidth for the waveguide appearing at the interface were optimized. A comprehensive survey of rod and hole size values reveals that the achieved group index bandwidth product of 0.72 is primarily due to the high bandwidth achieved within the optimized structure. Furthermore, our results confirm that rotating the square rods can further enhance slow light parameters, leading to a significantly higher group-index-bandwidth product than traditional semiconductor photonic crystal waveguides. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method to design an ultra-small photonic integrated biosensor to detect cancerous cells. The proposed biosensor is based on the self-phase modulation in PhC-SOA, inducing a frequency shift on a pulse traveling through the device. The amount of the frequency chirp depends on the group velocity of the active medium waveguide being determined by the refractive index of the microfluidic infiltrating the holes around the waveguide. The refractive index of the microfluidic is also determined by the cell type that can be normal or cancerous. Since the refractive index of a cancerous cell is higher than that of a normal one, the group index of the waveguide and the output chirp will decrease. By measuring the amount of the output chirp, we can detect the cell type. The Simulation results showed that for a 0.02 change in the refractive index of the cell, a 3.71 nm central wavelength shift occurred for a 10-ps 7-mW gaussian pulse input with a central wavelength of 1533.53 nm. In terms of the wavelength shift, the sensitivity and figure of merit are 185.5 and 530, respectively. To detect the cell type, we integrated a PhC channel drop filter to drop the chirped signal due to the cancerous cell infiltration. Designing an appropriate PhC-CDF leads to achieving an ultra-small cancerous detection cell biosensor with more than 97% precision. [ABSTRACT FROM AUTHOR]

A surface plasmonic waveguide made of metal–insulator–metal (MIM) capable of generating triple Fano resonances is proposed and numerically investigated for multi-biological parameter sensing as well as tunable slow light. The waveguide is made up of a bus waveguide with a silver baffle, a square split-ring cavity with a square center (SSRCSC), and a circular ring cavity with a square center (CRCSC). Based on the triple Fano resonances, human blood temperature and plasma concentration are measured simultaneously at different locations in the waveguide, and the maximum sensitivities were 0.25 nm/°C and 0.2 nm·L/g, respectively. Furthermore, the two biological parameters can be used to achieve tunable slow light, and it was found that the group delay responses to human blood temperature and plasma concentration all conformed to cubic functions. The MIM waveguide may have great applications in future nano-sensing of multiple biological parameters and information processing of optical chips or bio-optical chips. [ABSTRACT FROM AUTHOR]

Compact slow light devices are essential components for performing data caching and signal processing in photonic integrated loops. In this article, 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. [ABSTRACT FROM AUTHOR]

We have numerically studied a tunable dual‐spectral plasmon‐induced transparency metamaterial structure based on Dirac semimetal films in the terahertz region. The structure was composed of three length‐variant parallel coplanar strips. The dual‐spectral plasmon‐induced transparency is mainly induced by the bright‐bright modes coupling between neighboring Dirac semimetal strips. By adjusting the Fermi energies of Dirac semimetal strips, the individual and synchronous modulation of the dual‐transparency window in resonance frequency, bandwidth and strength can be obtained, respectively. Simultaneous change of the Fermi energies of all the strips can achieve an overall frequency shift of the dual‐transparency window, with the frequency modulation depth of 21.7% and 20.0%, respectively. The maximum group delays of 5.26 and 3.57 ps for each window were calculated in our proposed structure. The simulation results demonstrated the potential of the proposed structure to expand the applications for slow‐light systems, filters, and switchers in the terahertz region. [ABSTRACT FROM AUTHOR]

We propose a multiple-mechanical-mode-coupling nanomechanical system comprising three nanomechanical resonators (NRs) with different frequencies and each two NRs able to interact with each other. By weaving different NRs and controlling the coupling of NRs, the nanomechanical system can be series-, parallel-, or network-coupled nanoresonators network. Using two-tone fields to drive quantum dot implanted in one NR, we investigate the coherence optical responses and absorption spectrum manifested as a triple Fano resonance. Furthermore, each Fano resonance peak of the triple Fano resonance that induced the coherent optical propagation were demonstrated. The numerical results indicate that the slow light and the slow-to-fast light transition can be obtained by manipulating the interaction of NRs. These findings imply that the multiple-mechanical-mode coupling system can be a promising integration platform to achieve chip-scale applications in quantum information processing.

Buffering capability based on the slow light properties of silicon-polymer photonic-crystal coupled cavity waveguide (SP-PC-CCW) was set forth. We focused on reducing the dispersion and enhancing the buffering capability, including storage capacity, storage time, and physical size of each bit by appropriately adjusting the radii of the silicon filled rods in the first, second rows of the polymer-photonic-crystal slab, and the radius of the central cavity. We fulfilled the highest favorable value of the longest storage time of about 554.60ps and the highest storage density as 0.125464 bit/μm which is 1.72 times of the highest reported in PC-CCW micro-optical buffer. A polymer is used for the future incorporating electro-optic effect in buffers to realize dynamic controlling of optical properties. The results have been validated by the finite-difference time-domain (FDTD), in which a higher Q value resembles a longer buffering time of field inside the cavity. Moreover, the accumulation process of energy in the cavity contributes to the delay time, and thus higher quality factor corresponds to longer accumulation time, leading to more delay time. The proposed SP-PC-CCW may find applications in micro-integrated optical circuits for optical-signal processing, all-optical communication, and optical computers. [ABSTRACT FROM AUTHOR]

A tunable and switchable plasmon-induced transparency (PIT) effect in the near-infrared region (NIR) is achieved in a borophene-based metasurface, which consists of a periodic array of parallel double-layer borophene nanoribbons (BNRs). The upper- and lower-layer BNRs fulfill two plasmonic bright modes exciting and coupling for PIT phenomenon generation. By changing borophene electron density, the PIT window can be not only tuned to varying resonance frequency, but also adjusted for switching modulation. The calculation results reveal that as the electron density increases from 2.4 × 1019 to 5.6 × 1019 m−2, the PIT resonance frequency correspondingly shifts from 150 to 220 THz, and a maximum amplitude modulation depth (MD) of the PIT window reaches 98.3% at 193.55 THz ( λ = 1.55 μ m ). Moreover, the slow light characteristics of the proposed metasurface are analyzed in detail using the well-controlled group delay. Such a switchable and broadband tunable metadevice can expand the applications for PIT effect in active slow light, plasmonic sensing, and optical modulator areas. [ABSTRACT FROM AUTHOR]

By analytically solving the density matrix equations of a three-level atomic system interacting with two coherent laser fields and an incoherent pumping field under steady-state condition, we have derived the expressions for the absorption and dispersion (and thus group index and group velocity), and population difference as a function of the intensity, frequency, polarization and phase parameters of the laser fields. We have demonstrated that the appearance of spontaneously generated coherence—SGC (characterized by the polarization and non-orthogonality of the electric dipole moments) fundamentally changes the atomic optical responses. By adjusting the strength of SGC and/or incoherent pumping rate, the medium can switch between absorption and amplification regimes, between normal dispersion and anomalous dispersion, and thus light propagation in the medium can switch from slow light to fast light and vice versa. In particular, we have also found that in amplification regime the light is slowed down considerably. Amplifying and slowing light also become more efficient as incoherent pumping rate increases. In addition, the presence of the SGC and incoherent pumping field leads to a sensitive dependence of the atomic responses on the relative phase of the laser fields. Namely, the absorption, dispersion, and group index vary periodically with relative phase. [ABSTRACT FROM AUTHOR]

In this paper, a Plasmonic Photonic Crystal (PPhC) Waveguide structure is proposed, which is appropriately designed to support dispersionless slow plasmonic wave with group velocities between c/20 and c/50. Two important features of photonic crystals are manifested in the proposed structure; excitation of plasmonic waves and the slow light phenomenon. Introducing a silver stripe in the structure not only supports the propagation of plasmonic waves but also creates a TM bandgap which substantially leads to the creation of slow plasmonic waves. Numerical simulations confirm the plasmonic nature of the excited wave and the strong attenuation in the bandgap region. In addition, our simulations clarify more enhancement of light for the slower guided waves, which originates from the combination of plasmonic waves' confinement and high interaction of slow light with PPhC. The propagation length and quality factor of the proposed PPhC waveguide are calculated. It is shown that the slowest wave has the maximum enhancement, minimum propagation length, and quality factor. The trade-off between group velocity and enhancement factor can be balanced appropriately in order to have desired propagation length. Demonstration of the TM bandgap and high enhancement factor suggests the use of the proposed structure for the nonlinear application of all-optical devices, particularly soliton propagation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pushing a tunable metamaterial magnetic plasmon resonance with a narrow linewidth into the ultraviolet region still remains a challenge, which is desirable for the applications of optoelectronic devices in the ultraviolet (UV) range. Here, a thermally tunable narrow UV magnetic plasmon induced transparency (PIT) is explored in a metamaterial consisting of Si vertical split ring resonator (Si VSRRs) array. With the 3D metamaterials suspended in air to minimize the dielectric substrate effect, the plasmonic interference between the bright broad Si UV magnetic plasmon and the dark narrow Wood-Rayleigh anomaly mode produces a narrow PIT with a bandwidth of 5.2 nm and a Rabi splitting energy of 87 meV in the UV, revealed by the coupled Lorentz oscillator theory. Moreover, a dynamic tuning of the UV magnetic PIT and the associated slow light is achieved via temperature change of the encapsulated ethanol. With a high-level sensitivity of 180 nm/RIU and a figure of merit of 45, the lifted Si VSRR is applicable to detecting sub nanometre-thick analytes, indicating the potential for developing UV plasmonic biosensing. [ABSTRACT FROM AUTHOR]

The bound states in the continuum (BICs) are desired for high-performance optical devices. The structures composed of gratings and cavities were investigated. Grating waveguide modes (GWMs) are excited by the grating in structures. When the symmetry of the structure is broken, the positive and opposite GWMs couple and generate upper- and lower-coupled modes. Two coupled modes show different properties, such as the Fabry-Pérot (F–P) BIC in lower-coupled mode and the symmetry-protected (SP) BICs in upper-coupled mode. The special properties indicate the two coupled modes are desirable for multifunctional applications. The radiation from the quantum emitter (QE) was enhanced 3030 times through the quasi-BIC of lower-coupled mode. The maximal group delay reached 6.1 ps by the quasi-BIC of the lower-coupled mode. The quasi-BIC of the upper-coupled mode generates high-performance absorption. Two coupled resonance modes are sensitive to polarization, which can be used for optical switching with a maximal amplitude modulation depth of up to 99.8% with an insertion loss of less than 0.008 dB. These results offer hope for developing multifunctional and high-performance devices through coupled resonance modes in the grating-cavity structures. [ABSTRACT FROM AUTHOR]

• Triple narrowband and broadband PAs from the deep-UV to visible range are achieved, explained by impedance matching theory. • The group index (n g) of the lifted Al VSRR array for slow light can reach as large as 2.5 × 103 in the UV range. • Ultrasensitive biosensing in the UV region is achieved with FoM * of 1.1 × 106 at 312.5 nm. • Both the values of n g and FoM * are among the largest values in the UV range that have been recently reported. Achieving multiple perfect absorptions from ultraviolet (UV) to near-infrared (IR) region is practically important for metamaterial-based efficient harvesting of photons and biosensor. Here, we theoretically demonstrate a triple narrow and broad perfect absorptions (PAs) from visible to UV range in a lifted metamaterial made of aluminum vertical split-ring resonators (Al VSRR) on silica nanostrip /Al mirror. The three simultaneously achieved narrowband and broadband PAs with bandwidth of 283.3 nm, 8.9 nm and 18.2 nm are excited from magnetic plasmon resonance, surface plasmons polariton and plasmon standing wave mode, respectively, which is further explained by the impedance matching theory. The triple-band absorption peaks are further tailored by changing the size of the structure. The group index of the lifted Al VSRR array can reach as large as 2.5 × 103 in the UV range. Moreover, due to the designed metamaterial being lifted with the reduced substrate effect, the figure of merit (FoM *) and sensitivity (S) in the UV range are as high as 1.1 × 106 and 306 nm per refractive index unit‌ (306 nm/RIU), respectively. The proposed lifted metamaterial could have a considerable effect on the development of various UV plasmonic applications, including slow light nanodevices and optical sensor. [ABSTRACT FROM AUTHOR]

A double hexagonal single 'S' metamaterial (DHSSM), exhibiting plasmon-induced transparency (PIT) in its spectral response is studied in this paper. Amplitude modulation of the PIT window is achieved by varying the azimuth angle of substructure 'S'. Theoretical investigations into the PIT effect are conducted through numerical simulations. Moreover, an equivalent coupling circuit and Lorentz model are constructed to elucidate the PIT modulation mechanism. The results reveal that the PIT physical mechanism of the DHSSM has originated in destructive interference between bright-bright modes, which is directly excited by terahertz waves on the double hexagonal split rings and the 'S' substructure. For slow optical propagation performance, the structure has a high group delay (up to 41.92 ps) while allowing for the adjustment of the transparency window amplitude. The proposed metamaterial holds promising prospects for applications in slow light devices, switches, and filters within the terahertz frequency range. • Coupling between bright modes produces electromagnetically induced transparency at terahertz band. • The equivalent coupling circuit and Lorentz model reveal the amplitude modulation mechanism. • Strong scattering results in high group delay. • Amplitude modulation can be realized while maintaining high group delay. [ABSTRACT FROM AUTHOR]

A relatively simple metasurface structure is proposed to achieve a dynamically tunable slow light effect. The metasurface consists of two horizontal graphene strips and two vertical continuous graphene strips. Strong interference between the bright and dark modes enables the metasurface to generate a significant triple plasmon-induced transparency (PIT). Varying the coupling distance between the horizontal strips, double-PIT and triple-PIT can be transformed into each other. During the reduction of the transparent window, electromagnetic waves undergo strong phase changes, resulting in a higher group index. After structural optimization, the maximum time delay and group index can be as high as 2.624 ps and 3934, surpassing comparable slow light devices. The proposed patterned graphene metasurface provides theoretical guidance for designing high-performance slow light devices for optical storage, nonlinear optics and quantum optics. [Display omitted] • Based on graphene strips for achieving triple plasmon-induced transparency (PIT) effect. • The PIT effect can be dynamically regulated by the Fermi levels of graphene. • Varying the coupling distance between the two horizontal graphene strips, the triple-PIT can evolve into a dual-PIT. • The proposed metasurface exhibits outstanding slow-light performance with a group index up to 3934. [ABSTRACT FROM AUTHOR]

We theoretically demonstrate the ultraviolet (UV) high-order magnetic plasmon induced reflection (PIR) by lifting metamaterials consisting of three-dimensional aluminum split-ring resonators (3D-AlSRRs) with the effect of substrate being reduced. The strong plasmonic coupling between the second-order magnetic plasmon (2nd MP) of the lifted 3D-AlSRRs and the surface plasmons polaritons propagated on the Al substrate is achieved and leads to an ultranarrow PIR with linewidth of 4.6 nm in the UV range. The UV PIR effect is theoretically explained by an analytical Fano coupling model. In addition, the lineshape and position of the UV 2nd MP induced PIR can be artificially adjusted through varying the geometric parameters. The maximum of the group index of about 120 is achieved in the UV range. In addition, the sensitivity (S) and figure of merit (FoM) of the lifted 3D-AlSRRs are obtained to be 240 nm/RIU and 52, respectively. Our designed 3D metamaterials open a new path for the designing of multi-functional devices for such as slow-light and high sensitive optical sensor in the UV range.

Electromagnetically induced slow-light medium is a promising system for quantum memory devices, but controlling its noise level remains a major challenge to overcome. This work considers the simplest model for such medium, comprised of three-level Λ-systems interacting with bosonic bath, and provides a new fundamental trade-off relation in light–matter interaction between the group velocity of light and the Fano factor of photon current due to radiative transitions. Considering the steady state limits of a newly derived Lindblad-type equation, we find that the Fano factor of the photon current maximizes to 3 at the minimal group velocity of light, which holds true universally regardless of detailed values of parameters characterizing the medium. [ABSTRACT FROM AUTHOR]

We propose a novel acousto-optic (AO) devise using suspended fishbone nanobeams based on phononic and photonic potential well (PnPW and PtPW). We aim to reduce the traditional device size and eliminate the need for mirror regions in 1-D nanobeam cavity. By manipulating the frequencies of slow sound (SS) and slow light (SL) modes through geometric parameters, we can create potential wells for phonons and photons. The potential wells concentrate the waves inside the resonant cavity simultaneously, leading to an increase in AO coupling rate. We demonstrate the capability of potential wells in improving the AO coupling rate and investigate the impact of both wells. Some distribution of the phonons may affect the photons with a negative contribution, leading to a decrease in the coupling rate. Careful selection of appropriate acoustic and optical modes can overcome this limitation, making this structure a promising candidate for designing AO devices in silicon photonics. [ABSTRACT FROM AUTHOR]

A metal–insulator-metal (MIM) structure consisting of a semi-circular resonant cavity (SCRC) and a circular split-ring resonator (SRR) is proposed and designed for optical sensing applications. The coupling between the SCRC and SRR can create dual Fano resonances in the visible range. The optical responses of the structure including transmittance spectra and magnetic field distributions are investigated using finite-difference time-domain (FDTD) method. According to the calculated transmittance spectra, the proposed optical sensor can support double Fano resonances as a result of the interaction between the narrow-band mode of SRR and broadband mode of SCRC. The light-matter interaction at the Fano resonance frequencies is highly enhanced so that a maximum sensitivity and figures of merit (FOM) of 579 nm/RIU and 12.46 are obtained, respectively. Our proposed design also exhibits a great linearity R2 value of 0.999987. For the sake of completeness, it is shown that the structure can result in an optical delay of about 0.05 ps corresponding to a group index of 14.6 that is potentially useful for plasmonic nanosensors and slow-light devices in the visible range of the spectrum. [ABSTRACT FROM AUTHOR]

Si photonic foundry fabricated cascaded and continuous spiral shaped silicon nitride (SiN) waveguides that incorporate Bragg grating structures were explored to produce an on-chip true-time delay line. A time-domain measurement method was used to characterize the delay time of the grating waveguides near their photonic band edge where it exhibits the strongest slow light effect. The highest group index extracted from cascaded SiN grating waveguides is 19.7 corresponding to a total delay time of 5.48 ns in a full length of 12.49 cm that consumes a surface area of 2.66 mm2. A continuous spiral SiN grating waveguide was also fabricated which produces a delay time of 3.78 ns in a length of 5.47 cm with a surface area consumption of 0.88 mm2.

The geometric parameters of periodic units, which influence the refractive/reflective behaviors of grating waveguides, are usually designed using intuition combined with meticulous trial-and-error, making the design extraordinarily time-consuming and computationally intensive. In this work, we proposed an effective method based on deep learning to meet this challenge. Concretely, we employed fishbone slow-light waveguides as the object to be optimized, whose unit cell has multiple degrees of freedom, and trained a deep neural network (DNN) to predict their geometric parameters with the given discrete group index curves as the input. Our design is oriented for high group index and near-zero group velocity dispersion (GVD). To verify this functionality, we performed the controllable inverse design of GVD while keeping the group index at the same level (about 24), which made the bandwidth increase by 53.8% at the same time, and further explored near-zero GVD structures with a group index of 30.76/41.30/51.90. Our results lay the groundwork for the rapid design of complex slow-light grating waveguides. [ABSTRACT FROM AUTHOR]

Fano resonance is based on plasmonic metasurfaces and has many applications in all kinds of fields. In this paper, we propose an independently switchable double-layer raster structure based on graphene. Depending on the highly adjustable nature of graphene, the Fermi energy level can be adjusted to control the Fano resonance at different wavelengths. The equivalent resonator coupling mode method is used to simulate the Fano resonance, and the transmission spectrum fits well. Functional switch at different wavelengths can be achieved using Fano resonance technology. The simulation obtained a fantastic group refractive index of the designed structure, indicating that there is a possibility to apply it in slow light. The effect of the environmental refractive index on sensing performance was studied and we found the structure has great potential in making high-sensitivity sensors. To sum up, it is hoped that this structure can make a great contribution to the manufacture of integrated optics. [ABSTRACT FROM AUTHOR]

In this study, a two-dimensional low-symmetric photonic crystal (PC) configuration with elliptical geometry is presented and its slow-light (SL) effect is investigated. Reducing the symmetry in the PC unit cell provides slow modes at the higher transverse electric bands. The calculated group index and the corresponding normalized bandwidth equal to {ng, BW}={63.56, 0.0065}. That corresponds to a value of figure of merit (FOM)=0.4344 defined by the product of the average group index and the normalized bandwidth, FOM=g>BW, which is comparable to the values available in literature. Tracing the whole edges of the Brillouin zone, strongly excited SL modes are observed only along Γ-X but not along Γ-X' or Γ-M. That condition allows for the design of low-symmetric PC waveguides with finite thicknesses at the expense of lowering group index value. The SL effect is still obtained for the proposed low-symmetric PCs having finite thicknesses, which is numerically proved via finite-difference time-domain methods. It is important to note that non-dispersive SL Bloch modes exist through the non-zero k-vector components of Brillouin zone. Hence, such a defect-free (without either point- or line- defect) SL PC design may have a great potential for the use of compact photonic devices such as in optical switching and biochemical sensing applications. [ABSTRACT FROM AUTHOR]

Tunable slow light systems have gained much interests recently due to their efficient control of strong lightâ€"matter interactions as well as their huge potential for realizing tunable device applications. Here, a dynamically tunable polarization independent slow light system is experimentally demonstrated via electromagnetically induced transparency (EIT) in a terahertz (THz) metasurface constituted by plus and dimer-shaped resonators. Optical pump-power dependent THz transmissions through the metasurface samples are studied using the optical pump THz probe technique. Under various photoexcitations, the EIT spectra undergo significant modulations in terms of its resonance line shapes (amplitude and intensity contrast) leading to dynamic tailoring of the slow light characteristics. Group delay and delay bandwidth product values are modulated from 0.915 ps to 0.42 ps and 0.059 to 0.025 as the pump fluence increases from 0 to 62.5 nJ cmâˆ'2. This results in tunable slow THz light with group velocities ranging from 2.18 Ă— 105 m sâˆ'1 to 4.76 Ă— 105 m sâˆ'1, almost 54% change in group velocity. The observed tuning is attributed to the photo-induced modifications of the optoelectronic properties of the substrate layer. The demonstrated slow light scheme can provide opportunities for realizing dynamically tunable slow light devices, delay lines, and other ultrafast devices for THz domain. [ABSTRACT FROM AUTHOR]

In this article, we investigate the effect of reducing the speed of light by applying an electric field. This method is called tunneling-induced transparency (TIT). The research is based on the quantum structure of the ten layers of gallium arsenide and quantum dots of indium arsenide. We simulate and examine the transmission capacity of this device in terms of passing the wavelengths of the optical window. By widening the frequency transparency window, we can increase the light transmission limit of the probe. After passing the electric field of the probe light through a device based on quantum dots, the group velocity is predicted to be decreased by about 3 million times, which is about twice as much as similar work reported before Borges et al. (Phys Rev B 85:115425, 2012). Our main device is made from gallium arsenide, the dots are made from indium arsenide, and their surface distance from each other is 50 nm. [ABSTRACT FROM AUTHOR]

Topological photonics offers enhanced control over electromagnetic fields by providing a platform for robust trapping and guiding topological states of light. The topological rainbow can separate and distribute different wavelengths of topological photonic states into different positions, but related topological devices have not yet been fully explored. In this work, topological rainbows are realized by inserting a sandwiched gradient structure in the topological waveguide to realize the topological edge states. A robust one‐way slow‐light coupling state is realized to broaden the frequency range of the formed topological rainbow with the robust transmission. Thus, multiple topological rainbows are realized by combining the topological property with immunity to backscattering and coupling states of the slow light. Accordingly, light can spread, separate, and thus be trapped at different positions in different directions. This work provides a new way to reconfigure the topological rainbow and brings opportunities to study nanophotonic topological devices. [ABSTRACT FROM AUTHOR]

We theoretically investigate the Rabi-like splitting in the absorption spectrum of a single electron spin mediated by Majorana fermions in a hybrid semiconducting nanowire/superconductor system. The absorption spectra can display the symmetrical splitting phenomenon, and their related optical propagation such as fast light and slow light are investigated in different parametric regimes. When we consider implanting a spin into the carbon nanotube (CNT) resonator, the Rabi-like splitting in the absorption spectrum changes into asymmetric Fano resonance, which is accompanied by the rapid steep dispersion promising the slow- or fast-light effect, and even reaching tunable fast-to-slow light propagation (or vice versa) with controlling different parameter regimes. Moreover, we also investigate the role of the CNT resonator, which behaves as a phonon cavity enhancing the fast and slow light effect. [ABSTRACT FROM AUTHOR]

Slow light topological photonic crystal waveguide offers an attractive platform for enhancing light-matter interaction. We design a slow light rainbow trapping based on translational valley photonic crystal waveguides constructed by a gradient interface width. Through theoretical analysis and numerical calculation, the resulting structure supports topologically protected edge states at different frequencies. The edge state can be slowed down to zero group velocity and trapped at different positions. Moreover, the switch between slow light trapped states and transport states can be easily realized by tuning the structural parameter. Our work can help open up a new avenue to control the flow of light and find great potential for applications such as optical buffers and wavelength-division multiplexing. [ABSTRACT FROM AUTHOR]

The existence of a frozen mode in a periodic serpentine waveguide with broken longitudinal symmetry is demonstrated numerically. The frozen mode is associated with a stationary inflection point (SIP) of the Bloch dispersion relation, where three Bloch eigenmodes collapse on each other, as it is an exceptional point of order three. The frozen mode regime is characterized by vanishing group velocity and enhanced field amplitude, which can be very attractive in various applications including dispersion engineering, lasers, and delay lines. Useful and simple design equations that lead to realization of the frozen mode by adjusting a few parameters are derived. The trend in group delay and quality factor with waveguide length that is peculiar of the frozen mode is shown. The symmetry conditions for the existence of exceptional points of degeneracy associated with the frozen mode are also discussed.