Compact Plasmonic Structure Research Articles

Compact Plasmonic Structure Induced Mode Excitation and Fano Resonance

Metal-insulator-metal (MIM) waveguide has deep sub-wavelength field confinements, which makes it an important component in many aspects. In MIM structure, both of the symmetric and anti-symmetric modes could be supported. However, the anti-symmetric mode was hardly used in the SPP-based devices due to the critical excitation condition. Here, we demonstrate anti-symmetric mode excitation and Fano resonance in a compact MIM-based plasmonic structure. By changing the position of the output channel, the symmetric mode is suppressed and only anti-symmetric mode is excited. Then, we tune the position of the output channel; anti-symmetric and symmetric mode are both achieved. Furthermore, Fano resonance is realized due to the coupling between anti-symmetric mode and symmetric mode. In addition, we analyze the effects of the parameters of the structure on the transmission spectra, and a plasmonic refractive index sensor with sensitivity about 800 nm/RIU and 1100 nm/RIU based on different waveguide modes is also realized. The proposed structure provides a novel method to achieve anti-symmetric mode excitation, and it has important applications in nanophotonic devices such as filter, sensor, and photoswitch, and has important significance in achieving all-optical on-chip integration.

Analytical Methods of Equivalent Circuit Model and Transmission Matrix for a Plasmonic Switch with Sensing Capability in Near-Infrared Region

In this paper, the simultaneous switching and sensing capabilities of a compact plasmonic structure based on a conventional rectangular hole in a silver film are proposed and investigated. The proposed structure has ultrahigh sensitivity up to 3000 nm/RIU and high figure of merit of 170 RIU−1. Also, the simulation results show the potential of the presented refractive index sensor to detect malaria infection, cancer cells, bacillus bacteria, and solution of glucose in water. Simultaneously, by changing the incident lightwave polarization, the structure behaves like a plasmonic switch, which has high extinction ratios of 15.81, 31.20, and 25.03 dB at three telecommunication wavelengths of 850, 1310, and 1550 nm, respectively. The ultrafast response time of 20 fs is achieved for the wideband application of the switching capability at the wavelength range of 1056 to 1765 nm. Moreover, the equivalent circuit model and transmission (ABCD) matrix methods are derived to validate the simulated results. Simple design, good agreement between the numerical and analytical results, biomedical applications, ultrahigh sensitivity, and ultrafast performance of the proposed structure help this idea to open up paths for design and implementation of other multi-application plasmonic devices in near-infrared region. To the best of our knowledge, the mentioned analytical methods have not been studied former at near-infrared wavelengths. Therefore, the achievements could pave the way for verifying the simulation results of plasmonic nanostructures in future investigations.

Fano resonances based on plasmonic square resonator with high figure of merits and its application in glucose concentrations sensing

A compact plasmonic structure is proposed employing symmetrical metal–insulator-metal (MIM) waveguides coupled to the square resonator for nano-sensing applications, especially for water glucose sensing. Finite difference time domain method is chosen to derivate the output characteristics and magnetic-field distributions. Outcomes illustrate the Fano resonance in the output characteristics can be simply managed by varying the inner and outer lengths and the refractive index of the square cavity. Also, between Fano resonance wavelength and resonator length, a linear behavior exists. These features suggest that physical parameters provide flexibility to propose the structure. Our plasmonic device produces a sensitivity and figure of merit of about 6400 nm/RIU and 1 × 104, respectively. By utilizing the mathematical model for water refractive index, we aim to develop a sensor structure to detect the glucose concentration in water. This designed sensor may discover significant applications in future nanosensing domain.

Metal–insulator–metal waveguide‐coupled asymmetric resonators for sensing and slow light applications

In this study, a compact plasmonic structure for realising plasmon-induced transparency is proposed and numerically investigated by using the finite-difference time-domain method. The suggested device consists of double side-coupled square ring resonators based on a metal–insulator–metal platform. The coupled mode theory is introduced to describe the spectral response of the proposed structure, which is verified by numerical simulations. By changing the geometrical and material parameters such as outer side length and width of square ring resonators and metal collision frequency, the transmission characteristics can be easily tuned. The simulation results show that the proposed plasmonic system is used as a sensor by filling the insulator region with different refractive index. The sensitivity and figure of merit of this sensor are calculated, 806 nm/RIU and 66 RIU –1 , respectively. It is found that the slow light effect can appear in the proposed structure. By design optimisation, the maximum value of the group index is achieved close to 65. Meanwhile, the group index profile is obtained for different values of geometrical parameters like coupling aperture widths. The proposed structure provides a new way to utilise in nanosensor devices and slow light systems.

Blue-detuned optical atom trapping in a compact plasmonic structure

We theoretically propose blue-detuned optical trapping for neutral atoms via strong near-field interfacing in a plasmonic nanohole array. The optical field at resonance forms a nanoscale-trap potential with an FWHM of 200 nm and about ∼370 nm away from the nanohole; thus, a stable 3D atom trapping independent of the surface potential is demonstrated. The effective trap depth is more than 1 mK when the optical power of trapping light is only about 0.5 mW, while the atom scattering rate is merely about 3.31 s−1, and the trap lifetime is about 800 s. This compact plasmonic structure provides high uniformity of trap depths and a two-layer array of atom nanotraps, which should have important applications in the manipulation of cold atoms and collective resonance fluorescence.

Ultra-High Sensitivity Nanosensor Based on Multiple Fano Resonance in the MIM Coupled Plasmonic Resonator

This paper proposes a compact plasmonic structure that is composed of a metal-insulator-metal (MIM) waveguide coupled with a groove and stub resonators, and then investigates it by utilizing the finite element method (FEM). Simulation results show that the interaction between the local discrete state caused by the stub resonator and the continuous spectrum caused by the groove resonator gives rise to one of the two Fano resonances, while the generation of the other resonance relies only on the groove. Meanwhile, the asymmetrical linear shape and the resonant wavelength can be easily tuned by changing the parameters of the structure. By adding stubs on the groove, we excited multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of 2000 nm/RIU and a figure of merit of about 3.04 × 103, which can find extensive applications for nanosensors.

Ultra-high Sensitivity Plasmonic Nanosensor Based on Multiple Fano Resonance in the MDM Side-Coupled Cavities

We propose a compact plasmonic structure comprising a metal-dielectric-metal (MDM) waveguide coupled with a side cavity and groove resonators. The proposed system is investigated by the finite element method. Simulation results show that the side-coupled cavity supports a local discrete state and the groove provides a continuous spectrum, the interaction between them, gives rise to the Fano resonance. The asymmetrical line shape and the resonant wavelength can be easily tuned by changing the geometrical parameters of the structure. Moreover, we can extend this plasmonic structure by the double side-coupled cavities to gain the multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of ∼1900 nm/RIU and a figure of merit of about ∼3.8 × 104, which can find wide applications for nanosensors.

Symmetry breaking induced mode splitting based on a plasmonic waveguide system

Mode splitting is numerically predicted in a symmetry breaking plasmonic waveguide system, which consists of a metal–insulator–metal structure with a square cavity. By introducing a baffle in the square cavity, the anti-symmetric waveguide mode is excited and the transmission properties analyzed in detail. Simulation results show that we can obtain a longer resonant wavelength by only increasing the length of the baffle. Using the relationship between the length h and resonant wavelength λ, we can get a resonant cavity with a quality factor (Q-factor) as high as Q ≈ 150. Furthermore, a compact 1 × 2 plasmonic wavelength demultiplexer is successfully achieved without increasing the total size of the structure, which is very conducive to integration. In addition, a refractive index sensor with a high sensitivity about 1320 nm/RIU is also realized. When the lateral symmetry of the structure is broken, the anti-symmetric waveguide mode splits into two high-order modes, and a typical Fano profile is also achieved. Our compact plasmonic structure may have potential applications in nanoscale optical switching, nanosensors, nanolasers, wavelength demultiplexers and slow-light devices in highly integrated optical circuits.

Subwavelength beam focusing via multiple-metal slits arranged along a triangle surface

A compact plasmonic structure is proposed to actualize the subwavelength beam focusing, through a metal slit array arranged along a triangular or trapezium surface profile. The incident light passes through the metal slits in the form of surface plasmon polaritons (SPPs) and then scattered into radiation fields. The constructive interference of radiation fields from individual slits with different depths and widths gives rise to beam focusing. The advantages of the proposed plasmonic lens are having a much smaller lateral dimension and broad working wavelength range. This is of importance for realizing densely integrated photonic circuits. The finite-difference time-domain (FDTD) method is employed to verify the proposed design. The simulation results indicate that the focal spot is beyond the diffraction limit.

Spectral Splitting Based on Electromagnetically Induced Transparency in Plasmonic Waveguide Resonator System

Spectral splitting is numerically investigated based on the electromagnetically induced transparency (EIT) in a nanoscale plasmonic waveguide resonator system, which consists of a square ring resonator coupled with a stub-shaped metal-insulator-metal (MIM) waveguide. Simulation results show that the transparency window can be easily tuned by changing the geometrical parameters of the structure and the material filled in the resonators. By adding another stub or (and) square ring resonator, multi-EIT-like peaks appear in the broadband transmission spectrum, and the physical mechanism is presented. Our compact plasmonic structure may have potential applications for nanoscale optical switching, nanosensor, nanolaser, and slow-light devices in highly integrated optical circuits.

All-optical EIT-like phenomenon in plasmonic stub waveguide with ring resonator

An optical phenomenon analogous to electromagnetically induced transparency (EIT) has been proposed and investigated numerically in a plasmonic system, which is composed of a single stub-shaped metal–insulator–metal (MIM) waveguide coupled with a ring resonator. The transmission properties of the system are simulated by the finite-difference time-domain (FDTD) method. The bandwidth of the EIT-like spectrum is mainly dependent on the coupling distance between the stub and ring resonator. The red-shift of EIT-like peak is nearly linearly proportional to the increase in the radius and the refractive index of ring resonator, as is confirmed by the theoretical calculations. Our compact plasmonic structure may find potential applications in highly integrated optical circuits, such as nanoscale filters and optical switching.