Search Results (59)

A kind of magnetoplasmonic resonators is numerically designed with hexagonally arrayed Au/bismuth iron garnet (BIG) bilayer nanodiscks on Au thin film layers. Multi-physics coupling calculation on their magnetoplasmonic resonance features suggest that there exists a strong resonant coupling between the surface plasmon excited by the hexagonal grating and the waveguide modes induced by Au-BIG-Au, which can significantly enhance the transverse magneto-optical Kerr effect. Interestingly, a new type of circular oscillating can be induced in the optical-transparent BIG layers as the thickness of BIG layers is between 2 nm and 22 nm. This circular oscillating exhibits a distinct thickness-dependent feature, which can be attributed to the near field interference of the excited localized plasmon resonance between the two interfaces formed by the middle BIG nanodiscs in the top Au nanodisks and the bottom Au thin film layers according to the simulation. These unique magnetoplasmonic features endow this kind of magnetoplasmonic resonators with a greatly enhanced refractive index sensing property, with a calculated figure of merit (FOM) value of up to 7527 RIU⁻¹. Full article

A dual-band tunable terahertz electromagnetically induced transparency (EIT) metamaterial is introduced. The EIT metamaterial consists of two rectangular split rings, two metal strips, and a patterned vanadium dioxide (VO₂) located at the back. The rectangular split rings serve as the bright resonator to generate two resonance valleys at distinct frequencies. The metal strips act as the dark resonator and are indirectly activated via the coupling influence of the bright resonator. The EIT metamaterial’s response mechanism is analyzed via the field effect and the two-particle model, with theoretical fitting results showing strong agreement with the simulation results. Moreover, VO₂’s conductivity is altered to dynamically control the EIT effect in both frequency bands. Two transparency windows, with modulation depths of 70% and 75%, are observed as the conductivity of VO₂ decreases. Simultaneously, the simulation results reveal a favorable slow light effect, with group delays reaching 51 ps and 74 ps at the transparency windows. The proposed metamaterial holds considerable promise for future modulator, filter, and slow light device applications. Full article

In this paper, we propose the use of a monolayer graphene metasurface to achieve various excellent functions, such as sensing, slow light, and optical switching through the phenomenon of plasmon-induced transparency (PIT). The designed structure of the metasurface consists of a diamond-shaped cross and a pentagon graphene resonator. We conducted an analysis of the electric field distribution and utilized Lorentz resonance theory to study the PIT window that is generated by the coupling of bright-bright modes. Additionally, by adjusting the Fermi level of graphene, we were able to achieve tunable dual frequency switching modulators. Furthermore, the metasurface also demonstrates exceptional sensing performance, with sensitivity and figure of merit (FOM) reaching values of 3.70 THz/RIU (refractive index unit) and 22.40 RIU-1, respectively. As a result, our numerical findings hold significant guiding significance for the design of outstanding terahertz sensors and photonic devices. Full article

We propose two types of structures to achieve the control of Fano and electromagnetically induced transparency (EIT) line shapes, in which dual one-dimensional (1D) photonic crystal nanobeam cavities (PCNCs) are side-coupled to a bus waveguide with different gaps. For the proposed type Ⅰ and type Ⅱ systems, the phase differences between the nanobeam periodic structures of the two cavities are π and 0, respectively. The whole structures are theoretically analyzed via the coupled mode theory and numerically demonstrated using the three-dimensional finite-difference time-domain (3D FDTD) method. The simulation results show that the proposed structure can achieve several kinds of spectra, including Fano, EIT and asymmetric EIT line shapes, which is dependent on the width of the bus waveguide. Compared to the previously proposed Fano resonator with 1D PCNCs, the proposed structures have the advantages of high transmission at the resonant peak, low insertion loss at non-resonant wavelengths, a wide free spectral range (FSR) and a high roll-off rate. Therefore, we believe the proposed structure can find broad applications in optical switches, modulators and sensors. Full article

The double resonance phenomenon of EIT is studied through the ladder three-level Rydberg system. A probe laser with the wavelength ${\mathsf{\lambda }}_{\mathrm{p}}=852.35$ nm is used to coupling the ground state 6S_1/2 to the middle state 6P_3/2, and a coupling laser with the wavelength ${\mathsf{\lambda }}_{\mathrm{c}}=509.08$ nm is implemented to couple the state 6P_3/2 to the Rydberg state 62D_5/2. A special optical scheme is designed, in which the co-propagating and counter-propagating configurations are both used. As a result, the double resonance of electromagnetically induced transparency (EIT) with the Rydberg atom is observed. By comparing the distance between the double peaks, it is found that the double resonance phenomenon comes from the Doppler effect, and the distance between the two resonance peaks in the absorption spectrum is related to the detuning of the resonant lasers. Full article

Optical microresonators supporting whispering-gallery modes (WGMs) have become a versatile platform for achieving electromagnetically induced transparency-like (EIT-like) phenomena. We theoretically and experimentally demonstrated the tunable coupled-mode induced transparency based on the surface nanoscale axial photonics (SNAP) microresonator. Single-EIT-like and double-EIT-like (DEIT-like) effects with one or more transparent windows are achieved due to dense mode families and tunable resonant frequencies. The experimental results can be well-fitted by the coupled mode theory. An automatically adjustable EIT-like effect is discovered by immersing the sensing region of the SNAP microresonator into an aqueous environment. The sharp lineshape and high slope of the transparent window allow us to achieve a liquid refractive index sensitivity of 2058.8 pm/RIU. Furthermore, we investigated a displacement sensing phenomenon by monitoring changes in the slope of the transparent window. We believe that the above results pave the way for multi-channel all-optical switching devices, multi-channel optical communications, and biochemical sensing processing. Full article

Bound states in the continuum (BICs), which are characterized by their high-quality factor, have become a focal point in modern optical research. This study investigates BICs within a periodic array of dielectric resonators, specifically composed of a silicon rectangular bar coupled with four silicon rectangular blocks. Through the analysis of mode coupling, we demonstrate that the interaction between the blocks significantly modulates the eigenmodes of the bar, causing a redshift in all modes and enabling the formation of electromagnetically induced transparency based on BICs (EIT-BIC). Unlike typical EIT mechanisms, this EIT-BIC arises from the coupling of “bright” and “dark” modes both from the rectangular bar, offering novel insights for nanophotonic and photonic device design. Further, our systematic exploration of BIC formation mechanisms and their sensing properties by breaking structural symmetries and changing environmental refractive indices has shed light on the underlying physics. This research not only consolidates a robust theoretical framework for understanding BIC behavior but also paves the way for high-quality factor resonator and sensor development, as well as the precise control of photonic states. The findings significantly deepen our understanding of these phenomena and hold substantial promise for future photonic applications. Full article

Dynamical manipulation of plasmon-induced transparency (PIT) in graphene metasurfaces is promising for optoelectronic devices such as optical switching and modulating; however, previous design approaches are limited within one or two bright/dark modes, and the realization of dual PIT windows through triple bright modes in graphene metasurfaces is seldom mentioned. Here, we demonstrate that dual PIT can be realized through a symmetry-engineered graphene metasurface, which consists of the graphene central cross (GCC) and graphene rectangular ring (GRR) arrays. The GCC supports a bright mode from electric dipole (ED), the GRR supports two nondegenerate bright modes from ED and electric quadrupole (EQ) due to the C₂v symmetry breaking, and the resonant coupling of these three bright modes induces the dual PIT windows. A triple coupled-oscillator model (TCM) is proposed to evaluate the transmission performances of the dual PIT phenomenon, and the results are in good agreement with the finite-difference time-domain (FDTD) method. In addition, the dual PIT windows are robust to the variation of the structural parameters of the graphene metasurface except for the y-directioned length of the GRR. By changing the carrier mobility of graphene, the amplitudes of the two PIT windows can be effectively tuned. The alteration of the Fermi level of graphene enables the dynamic modulation of the dual PIT with good performances for both modulation degree (MD) and insertion loss (IL). Full article

In this paper, we demonstrate that the absorption frequencies of the bimodal absorber shift with the coupling strength of the bright and dark modes. The coupling between the bright mode and the dark mode can acquire electromagnetically induced transparency, we obtain the analytical relationship between the absorbing frequencies, the resonant frequencies, losses of the bright mode and dark mode, and the coupling strength between two modes by combining the coupled mode theory with the interference theory. As the coupling strength between the bright mode and the dark mode decreases, the two absorption peaks gradually move closer to each other, inversely, they will move away from each other. The simulation employs three distinct metasurface structures with coupling of the bright and dark modes, thereby verifying the generality of the theoretical findings. Full article

We propose a scheme to investigate the interference properties of a double optomechanically induced transparency system, which involves two charged nanomechanical resonators, coupled via Coulomb interaction. The results show that the opening of transparency windows is caused by a destructive interference effect only in the weak optical coupling region. For strong optical coupling, normal mode splitting dominates the transparency phenomenon. In the intermediate region, both destructive interference and normal mode splitting contribute to the transparency windows. When the Coulomb coupling is much weaker than the optical coupling, the Coulomb interaction strength linearly determines the distance between the two transparency windows, and has nearly no influence on the destructive interference effect. Otherwise, the system will work in a nonlinear region. Full article

Coupling is a ubiquitous phenomenon observed in various systems, which profoundly alters the original oscillation state of resonant systems and leads to the unique optical properties of metasurfaces. In this study, we introduce a terahertz (THz) tunable coupling metasurface characterized by a four-fold rotation (C₄) symmetry-breaking structural array achieved through the incorporation of vanadium dioxide (VO₂). This disruption of the C₄ symmetry results in dynamically controlled electromagnetic interactions and couplings between excitation modes. The coupling between new resonant modes modifies the peak of electromagnetic-induced transparency (EIT) within the C₄ symmetric metasurfaces, simulating the mutual interference process between modes. Additionally, breaking the C₄ symmetry enhances the mirror asymmetry, and imparts distinct chiral properties in the far-field during the experimental process. This research demonstrates promising applications in diverse fields, including biological monitoring, light modulation, sensing, and nonlinear enhancement. Full article

Cross-polarization coupling between transverse electric (TE) and transverse magnetic (TM) whispering-gallery modes in an optical microresonator produces effects such as coupled-mode induced transparency (CMIT). The detailed analytical theory of this coupling indicates that the TE-to-TM and TM-to-TE couplings may have different strengths. Using an experimental setup centered around a hollow bottle resonator and polarization-sensitive throughput detection, that had been used in previous CMIT experiments, this asymmetry was confirmed and studied. By fitting the throughput spectra of both polarizations to the numerical output of a basic model, the asymmetry parameter defined as the ratio of the coupling amplitudes was determined from the output power in the polarization orthogonal to that of the input. The results of many experiments give a range for this ratio, roughly from 0.2 to 4, that agrees with the range predicted by the detailed theory. An analytical approximation of this ratio shows that the main reason for the asymmetry is a difference in the axial orders of the coupled modes. In some experimental cases, the orthogonal output is not well fitted by the model that assumes a single mode of each polarization, and we demonstrate that this fitting discrepancy can be the result of additional mode interactions. Full article

We analyze schemes of high-fidelity multi-qubit CNOT${}^{\mathrm{N}}$ and C${}_2$NOT${}^2$ gates for alkali metal neutral atoms used as qubits. These schemes are based on the electromagnetically induced transparency and Rydberg blockade. The fidelity of homonuclear multi-qubit CNOT${}^{\mathrm{N}}$ gate based on Rydberg blockade was limited by the undesirable interaction between the target atoms and by the coupling laser intensity. We propose overcoming these limits by using strong heteronuclear dipole–dipole interactions via Förster resonances for control and target atoms, while the target atoms are coupled by a weaker van der Waals interaction. We optimized the gate performance in order to achieve higher fidelity, while keeping the coupling laser intensity as small as possible in order to improve the experimental feasibility of the gate schemes. We also considered the optimization of the schemes of the C${}_2$NOT${}^2$ gates, where the fidelity is affected by the relation between the control–control, control–target and target–target interaction energies. Our numeric simulations confirm that the fidelity of the CNOT${}^4$ gate (single control and four target atoms) can be up to 99.3% and the fidelity of the C${}_2$NOT${}^2$ (two control and two target atoms) is up to 99.7% for the conditions which are experimentally feasible. Full article

The existence of surface plasmon polaritons in doped silicon micro-scale structures has opened up new and innovative possibilities for applications, such as sensing, imaging, and photonics. A CMOS-compatible doped Si plasmonic sensor is proposed and investigated. The plasmon resonance can be tuned by controlling the carrier density and dopant concentration. In this paper, we demonstrate that using silicon doped with phosphorus at a concentration of 5 × 10${}^{20}$ cm${}^{-3}$ can induce surface plasmon resonance in the mid-infrared region. Two ring resonators of two different radii based on metal–insulator–metal waveguide structures are studied individually. Then, the two ring resonators are integrated in the same device. When the two ring resonators are coupled and resonate at the same frequency; two distinct resonance spectral lines are generated with striking features that improve its potential use for sensing and modulation applications. The propagating plasmonic mode is studied, including its mode profile and bend loss. We evaluate the effectiveness of a microstructure gas sensor with dimensions of 15 $\mathsf{\mu }$m × 15 $\mathsf{\mu }$m by measuring its sensitivity and selectivity towards methane and ethane gases. Small alterations in the surrounding refractive index led to noticeable shifts in the resonance peak. The sensor achieved a sensitivity of 7539.9 nm/RIU at the mid-infrared spectral range around the 7.7 $\mathsf{\mu }$m wavelength. Furthermore, by combining the resonators, we can achieve a smaller full width at half maximum (FWHM), which will ultimately result in greater sensitivity than using a single-ring resonator or other plasmonic resonator configurations. Once the sensitivity and selectivity of the sensor are measured, the FOM can be calculated by dividing the sensitivity by the selectivity of the sensor, resulting in an FOM of 6732. Full article

This paper presents a metamaterial biosensor composed of dual-cut wires (DCWs) and quadruple split-ring resonators (QSRs), achieving polarization-independent plasmon-induced transparency (PIT) effects in the terahertz range. By leveraging the coupling between bright and dark modes, we observe a transparent window with a minimal loss at 1.22 THz. We investigate the physical mechanism of the PIT effect by analyzing the surface current distribution and electric fields. Simulations reveal that the PIT transparency shows a peak shift of up to 146.7 GHz with an analyte thickness of 14 μm. Moreover, as the refractive index of the analyte increases from 1.0 to 1.6, the biosensor’s theoretical sensitivity is calculated to be 281.25 GHz/RIU. Furthermore, we explore the application of the proposed DCW/QSR biosensor for the detection of bacteriophage viruses. Our simulation results demonstrate that the DCW/QSR biosensor serves as an effective sensing platform for detecting viruses such as PRD1 and MS2. These findings underscore the potential of our high-sensitivity metamaterial biosensor, which holds great promise in the field of biosensing, offering a practical and cost-effective approach to label-free biomedical detection. Full article