A Plasmonic Structure of Fano Resonance in the MIM Waveguide with r-Shaped Resonator for Refractive Index Sensor

A plasmonic structure of metal-insulator-metal (MIM) waveguide consisting of a single baffle waveguide and an r-shaped resonator is designed to produce Fano resonance. The finite element method uses the finite element method to analyze the transmission characteristics and magnetic field distributions of the plasmonic waveguide distributions. The simulation results exhibit two Fano resonances that can be achieved by the interference between a continuum state in the baffle waveguide and a discrete state in the r-shaped resonator. The Fano resonances can be simply tuned by changing geometrical parameters of the plasmonic structure. The value variations of geometrical parameters have different effects on sensitivity. Thus, the sensitivity of the plasmonic structure can achieve 1333 nm/RIU, with a figure of merit of 5876. The results of the designed plasmonic structure offer high sensitivity and nano-scale integration, which are beneficial to refractive index sensors, photonic devices at the chip nano-sensors, and biosensors applications.

Multiple Fano resonances based on clockwork spring-shaped resonator for refractive index sensing

A surface plasmon polarized structure consisting of two metal-insulator-metal (MIM) waveguide coupled with clockwork spring-shaped resonators are constructed in this paper, and its geometric parameters are controlled within a few hundred nanometers. The finite element method (FEM) and multimode interference coupled mode theory (MICMT) are used to simulate and theoretically calculate the optical response of the designed structure. By modifying the structural parameters of the system, the influence on the asymmetry of the Fano resonance line is studied. The changes of the transmission spectra at different refractive indexes are also investigated. Based on this asymmetric resonant line, the sensitivity and FOM* (figure of merit) value of the cavity with different parameters are measured. The sensitivity and FOM* under the best parameters are 1200 nm/RIU and 191.6, respectively. The surface plasmon structure proposed and the results in this paper are promising for applications in the field of high-performance sensing and micro-nano optical devices.

Super High Sensitivity Plasmonic Temperature Sensor Based on Square Ring Shape Resonator with Nanorods Defects

A super high sensitivity plasmonic temperature sensor via a metal-insulator-metal (MIM) waveguide system is presented in this paper, the waveguide structure is composed of a square ring shape resonator with nanorods defects and a nanodisk resonator. Finite difference-time domain method (FDTD) is used to study the structure’s transmission characteristics and electromagnetic field distributions. Results show that sensitivity will be increased due to the gap plasmonic in the nanorod defect, the nanodisk resonator provides more plasmonic resonant modes for sensing. The positions and intensities of plasmonic resonant modes can be tuned by the radius of nanorod defects and coupling distance. The calculated maximum refractive index and FOM are and 3500, respectively. Compared to the structure without nanorods, the sensitivity is enhanced 33% for mode 1. For temperature sensing, the proposed structure possesses a relatively high sensitivity of about . The proposed plasmonic structure provides a basis for designing high sensitivity nano-biosensing, refractive index sensing.

Nanoantennas Inversely Designed to Couple Free Space and a Metal–Insulator–Metal Waveguide

The metal–insulator–metal (MIM) waveguide, which can directly couple free space photons, acts as an important interface between conventional optics and subwavelength photoelectrons. The reason for the difficulty of this optical coupling is the mismatch between the large wave vector of the MIM plasmon mode and photons. With the increase in the wave vector, there is an increase in the field and Ohmic losses of the metal layer, and the strength of the MIM mode decreases accordingly. To solve those problems, this paper reports on inversely designed nanoantennas that can couple the free space and MIM waveguide and efficiently excite the MIM plasmon modes at multiple wavelengths and under oblique angles. This was achieved by implementing an inverse design procedure using a topology optimization approach. Simulation analysis shows that the coupling efficiency is enhanced 9.47-fold by the nanoantenna at the incident wavelength of 1338 nm. The topology optimization problem of the nanoantennas was analyzed by using a continuous adjoint method. The nanoantennas can be inversely designed with decreased dependence on the wavelength and oblique angle of the incident waves. A nanostructured interface on the subwavelength scale can be configured in order to control the refraction of a photonic wave, where the periodic unit of the interface is composed of two inversely designed nanoantennas that are decoupled and connected by an MIM waveguide.

A Nanoscale Structure Based on an MIM Waveguide Coupled with a Q Resonator for Monitoring Trace Element Concentration in the Human Body

In this study, a nano-refractive index sensor is designed that consists of a metal–insulator–metal (MIM) waveguide with a stub-1 and an orthogon ring resonator (ORR) with a stub-2. The finite element method (FEM) was used to analyze the transmission characteristics of the system. We studied the cause and internal mechanism of Fano resonance, and optimized the transmission characteristics by changing various parameters of the structure. In our experimental data, the suitable sensitivity could reach 2260 nm/RIU with a figure of merit of 211.42. Furthermore, we studied the detection of the concentration of trace elements (such as Na+) of the structure in the human body, and its sensitivity reached 0.505 nm/mgdL−1. The structure may have other potential applications in sensors.

A MIM Waveguide Structure of a High-Performance Refractive Index and Temperature Sensor Based on Fano Resonance

A plasmonic refractive index nanosensor structure consisting of a metal-insulator-metal (MIM) waveguide with two symmetrical rectangle baffles coupled with a connected-concentric-double rings resonator (CCDRR) is presented. In this study, its transmission characteristics were investigated using the finite element method (FEM). The consequences, studied via simulation, revealed that the transmission spectrum of the system presents a sharp asymmetric Fano profile due to the destructive interference between the wide-band mode of two rectangle baffles on the bus waveguide and the narrow-band mode of the CCDRR. The effects of the geometric parameters of the structure on the transmission characteristics were investigated comprehensively. A sensitivity of 2260 nm/RIU and figure of merit (FOM) of 56.5 were the best levels of performance that the designed structure could achieve. In addition, the system could act as a sensor for use for temperature sensing, with a sensitivity that could reach 1.48 nm/°C. The designed structure advances with technology with new detection positions and has good application prospects in other high-sensitivity nanosensor fields, for example, acting as a biosensor to detect the hemoglobin level in the blood.

Refractive Index Sensing Based on Multiple Fano Resonances in a Split-Ring Cavity-Coupled MIM Waveguide

A metal–insulator–metal (MIM) waveguide consisting of a circular split-ring resonance cavity (CSRRC) and a double symmetric rectangular stub waveguide (DSRSW) is designed, which can excite quadruple Fano resonances. The finite element method (FEM) is used to investigate influences of geometric parameters on the transmission characteristics of the structure. The results show that Fano resonances are excited by the interference between the DSRSW and the CSRRC. Among them, the resonance wavelengths of the Fano resonances are tuned by the narrow-band discrete state excited by the CSRRC, and the resonance line transmittance and profiles are tuned by the wide-band continuous state excited by the DSRSW. The sensitivity (S) can be up to 1328.8 nm/RIU, and the figure of merit (FOM) can be up to 4.80 × 104. Based on these advantages, the structure has potential applications in sensing in the sub-wavelength range.

Tunable Nanosensor With a Horizontal Number Eight-Shape Cavity in a MIM Waveguide System

Optical devices play an important role in different fields, such as refractive index detection in food processing and the biochemical industry. In our work, a novel nanoscale optical structure, composed of a metal-insulator-metal waveguide with a stub and a horizontal number eight-shape cavity (HNEC), is presented. The transmission properties of this structure are investigated in detail by using finite element method The effects of geometric parameters on sensing performance are studied in detail. Moreover, the influences of an asymmetric resonator caused by shifting central rectangular cavity of HNEC on transmission spectrum are discussed. The changing parameters of HNEC resonator have different effects on different resonance dips. Then, when the parameters of this presented structure are fixed as a of 540 nm, b of 340 nm, S of 0, l of 70 nm and g of 10 nm, this intriguing structure can serve as a refractive index sensor, whose maximum sensitivity can reach 1,500 nm/refractive index unit with a figure of merit of 75. Therefore, this structure will contribute to the development of miniaturization of optical devices.