In the paper, resonances of different waveguide structures with various vertical indirect coupled cavities were investigated by FDTD (finite difference-time domain). In the silicon cavity, Fano resonance could be observed at about 1430 nm. The coupling distance for the gold cavity/air cavity had less effect on the transmittance of the main waveguide but had a great influence on the transmission for water cavity in the visible region, which showed that water cavity could adjust resonance of waveguide structures. In addition, with the increment of refractive index n, the resonance peak at about 850 nm moved to the long wavelength (redshift). Dispersion rate about 2 × 10–3/nm indicated that the transparent dielectric selectively absorbed the surface plasmon polariton wave and the sensitivity of the waveguide structure designed in this paper has high stability for the refractive index of the main waveguide cavity. Obvious Fano resonance could be observed with the increase of refractive index for silicon cavity. Among the four dielectrics, silicon and water are suitable for studying Fano resonance and filter dielectrics.
相似文献In this paper, a high-resolution refractive index sensor is proposed based on a novel metal–insulator–metal plasmonic topology. The structure is based on a Si nano-ring located inside a circular cavity. It acts as an optical notch filter with a quality factor equal to 269. The proposed filter topology is numerically simulated using the finite difference time domain method. It is shown that the proposed filter can also act as a refractive index sensor with a sensitivity of 636 nm/RIU and a fairly high figure of merit (FoM) equal to 211.3 RIU−1. It is shown that the sensor can easily detect a refractive index change of ± 0.001 for dielectrics whose refractive index is between 1 and 1.2. For the refractive index range of 1.33 to 1.52, the maximum FoM of the sensor is 191 RIU−1. The simplicity of the design and its high resolution are the two main features of the proposed sensor which make it a good candidate for biomedical applications.
相似文献Three layers of periodic artificial metamaterial sensing structure (including the upper metal particles, intermediate dielectric layer, and the lower reflective layer) with ultra-narrow band absorption were designed. The resonance characteristics and sensing properties were analyzed by the finite difference time domain (FDTD) method. The effect of localized surface plasmon resonance (LSPR) was obviously observed at the resonance wavelength of 911 nm, and it achieves nearly perfect absorption of exceeding 98% with a full width at half maximum (FWHM) of 3.5 nm. In addition, a wavelength sensitivity of 542 nm/RIU with a figure of merit (FOM) of 155 was obtained in the refractive index (RI) range from 1.00 to 1.35, which has a wide range of applications. The results show that the proposed structure has high absorption and RI sensitivity, which is suitable for bioengineering and medical detection.
相似文献A dual-core and dual D-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor with silver and aluminum nitride (AlN) films is designed. The distribution characteristics of the electromagnetic fields of core and plasmon modes, as well as the sensing properties, are numerically studied by finite element method (FEM). The structure parameters of the designed sensor are optimized by the optical loss spectrum. The results show the resonance wavelength variation of 489 nm for the refractive index (RI) range of 1.36?~?1.42. In addition, a maximum wavelength sensitivity of 13,400 nm/RIU with the corresponding RI resolution of 7.46?×?10?6 RIU is obtained in the RI range of 1.41?~?1.42. The proposed sensor with the merits of high sensitivity, low cost, and simple structure has a wide application in the fields of RI sensing, such as hazardous gas detection, environmental monitoring, and biochemical analysis.
相似文献The polarization characteristics of high-birefringence photonic crystal fiber (HB-PCF) selectively coated with silver layers are numerically investigated using the full-vector finite element method (FEM). The fundamental mode coupling properties and polarization splitting effect are discussed in detail. Results show that the resonance wavelength, resonance strength, and splitting distance between two polarized modes can be adjusted significantly by changing the fiber structure, the diameter of silver rings, and the thickness of silver layers. A single-polarization filter at 1310 nm bands is proposed with the corresponding loss 500 dB/cm and full width half maximum (FWHM) only 23 nm. This work is very helpful for further studies in polarization-dependent wavelength-selective applications or other fiber-based plasmonic devices.
相似文献A single-polarization photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed. Finite element method is employed in simulating the PCF with gold-coated. The resonance wavelength can be modulated by changing the thickness of gold layer. At the resonance wavelength 1.55 μm, the loss of y-polarized mode is much larger than the loss of x-polarized mode. When the fiber length is set to 2 mm, the value of extinction ratio reaches to −118.7 dB, the y-polarized mode is suppressed and only x-polarized mode can be guided. The fiber is applicable in the production of single-polarization filter. The PCF has a simple structure and a big error tolerance, it has a good practicability.
相似文献Dividing a metal nanoparticle into smaller components and the occurrence of the plasmonic phenomenon in the gap between these components can improve the sensitivity of the detector to variation of the refraction coefficient of liquid. In this paper, in a constant volume of metal, a golden disk is divided into two rings and one smaller disk. With a proper arrangement of these components, the surface plasmon resonance phenomenon takes place at the wavelength of 945.7 nm. The occurrence of this phenomenon increases the field in the distance between nanoparticles surrounded by liquid. The sensitivity of the detector that designed using nanodisks is 300 nm/RIU while it increases to 500 nm/RIU for the new structure. The increase of LSPR displacement, for a variation of 0.01 in the liquid refraction coefficient, from 3 nm for a disk to 5 nm for a proposed structure verifies a 67% improvement in the sensitivity of the sensor.
相似文献This paper deals with the development and analysis of D-Shaped photonic crystal fiber (PCF) biosensors using surface plasmon resonance (SPR). A thin metal layer is deposited on the outer flat surface of the PCF that behaves as the plasmonic material. Analyte is filled in the outermost peripheral region of metal layer. Finite element method (FEM) with perfectly matched layer (PML) is applied to analyze the proposed sensors. Mode analysis is performed on the proposed structures to evaluate various parameters of SPR-based PCF sensors. Three D-shaped PCF structures have been proposed with silver (Ag), gold (Au) and two-half layers of both (Ag-Au) on its flat surface. The first two structures are analyzed to the range of wavelength where the SPR will occur to facilitate understanding of the third structure. It is observed that the structures with one metal have only one sensitive plasmonic peak whereas the structure with two metal layers has two sensitive plasmonic peaks, making it suitable candidate for two-molecule sensing present in a sample analyte. Good sensitivities and resolutions are achieved for both plasmonic peaks.
相似文献In this paper, a wavelength demultiplexing structure based on multi-teeth-shaped metal-insulator-metal (MIM) plasmonic waveguide is designed and numerically studied using the finite-difference time-domain (FDTD) method. Investigating the characteristics of a multi-teeth-shaped plasmonic waveguide structure reveals that with the design of the structure, it was possible to create a mode inside the bandgap of the filter. Based on the created mode inside the bandgap of the filter, the demultiplexer structure has been proposed and investigated. By changing the geometric parameters of the structure, the transmission wavelength of the demultiplexer channel can be adjusted. The proposed demultiplexer can be used in integrated optical circuits.
相似文献In this paper, a graphene strip is introduced into a metal-insulator-metal (MIM)-integrated square cavity hybrid structure; the transmission spectra are theoretically investigated by the finite different time domain (FDTD) methods. An asymmetric Fano resonance dip that has high figure of merit (FOM) value appears in the transmission band. According to the multimode interference coupled mode theory (MICMT) analytical method, the Fano resonance originates from the coherent coupling between TM10 cavity magnetic mode and graphene plasmonic resonance electric mode. The center wavelength, full width at half maximum (FWHM), and FOM value of the Fano resonance can be tuned dynamically by altering the Fermi level of the graphene. Through breaking the symmetry of the hybrid structure or introducing double graphene strips with different Fermi level into hybrid structure, double Fano resonance are realized. This study can provide some theoretical basis and design reference for designing ultrahigh sensitivity plasmonic sensor.
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