Theoretical Investigation Of Novel Nanosensors Based On Surface Plasmon Polaritons

In the field of photonics, the optical diffraction limitation has restricted the development of the integration of photonic devices. Therefore, this problem about how to break through the diffraction limit and then guiding and manipulating the light in nanoscale has become a hot spot in the research of nanophotonics. With the continuous development of nanotechnology, Surface plasmon polaritons provide a possible solution to solve this outstanding problem. Due to its ultra-sensitive property to the metal nanostructure and the surrounding medium, it has important applications in the field of sensing. Applying surface plasmon polaritons in sensing will help to promote the production of a new generation of micro-nano photonic sensor with high sensitivity and high integration and this will have great potential application value. This paper mainly investigates the sensing structure based on metal–insulator–metal(MIM) waveguide with side-coupled cavity using the Finite-difference time-domain(FDTD) method. The main research contents in this paper are as follows:First, based on the Maxwell equations, the theory of surface plasmon polaritons excited on the interface between metal and dielectric and its basic characteristics are deduced in detail. Then the dispersion of the MIM waveguide is also introduced.Second, based on the structure consisting of an MIM waveguide and a side-coupled nanodisk resonator, we investigate its sensing characteristics of the structure using a finite-difference time-domain(FDTD) method. And analyze the influence of its structural parameters on the sensing characteristics of the structure.Third, we investigate a novel and compact plasmonic sensing structure based on an MIM waveguide with a side-coupled hexagonal cavity. The sensing structure has been numerically and theoretically investigated using the FDTD method and temporal coupled-mode theory. The numerical simulation results show that the resonance dips of the structure have a high resonant transmission contrast ratio and the resonance wavelengths have a near-linear relationship with the refractive index of the dielectric material in the cavity. The effects of the geometrical parameters on the transmission and sensing characteristics of the structure are analyzed in detail. In addition, based on the relationship between the temperature and the refractive index of the dielectric, the temperature-sensing characteristic of the structure based on the refractive-index sensor is also discussed in this paper.Last, based on the sensing structure constructed of an MIM waveguide with a side-coupled hexagonal cavity, we propose and investigate a plasmonic temperature-sensing structure, which is based on an MIM waveguide with dual side-coupled hexagonal cavities. Based on the linear relationship between the resonance dip and the environment temperature, the temperature-sensing characteristics are discussed. The temperature sensitivity is influenced by the side length and the coupling distance. Moreover, two concepts of optical spectrum interference and misjudge rate are introduced to study the temperature sensing resolution based on spectral interrogation. These two concepts provide the methods to analyze numerically the overlap degree of the spectra and the accurate judgment rate for them. This provides a theoretical support for the analysis of the resolution of the sensor, then it may promote the development of the sensors with high resolution.