Ultra-sensitive And Tunable Plasmonic Sensor Based On The Fano Resonance

Surface plasmon is a one of the most popular topics in nanophotonics,which refers to electromagnetic wave induced collective oscillation of free electron at the surface of metal.Surface plasmon includes the localized surface plasmon?LSP?and surface plasmon polaritons?SPPs?.Due to the characteristics of remarkable enhancement of electrical filed and concentrating light beyond the diffraction limit,plasmonic waveguide structures have attracted much attention in recent years.Compared with other plasmonic waveguide,metal-dielectric-metal?MDM?holds the properties of high confinement of field,transmission distance with several tens of microns,simple structure and ease of fabrication,so it has been widely studied.With the rapid development of nanotechnology and plasmonics,it is possible to control light at the nanoscale.Researchers have investigated the Fano resonance in MDM waveguide and discussed the corresponding applications in sensing,switching,filtering,etc.,which provides basis for the development of high-performance and on-chip photonic device.In this paper,the research contents are as follows:?1?Based on Fano resonance,an on-chip high-sensitivity sensor,composed of two waveguides coupling with a symmetry breaking ring resonator,has been theoretically and numerically investigated.The established theoretical model agrees well with the finite-difference time-domain simulations,which reveals the physics of Fano resonance.Differing with the coupled cavities,the Fano resonance originates from the interference between symmetry-mode and asymmetry-mode in a single symmetry-broken cavity.The spectral responses and sensing performances of the plasmonic structure rely on the degree of asymmetry of cavity.In particular,the plasmonic sensor can detect the refractive index changes as small as 10^-5,and the figure of merit?FOM?of symmetry-breaking cavity structure is 17 times larger than that of symmetrical cavity system.Additionally,the sensitivity to temperature of ethanol analyte achieves 0.701nm/^?C.Compared with the coupled cavities,the on-chip high-sensitivity sensor using a single cavity is more compact,which paves the way toward highly integrated photonic devices.?2?A simple and tunable plasmonic sensor,composed of a slot cavity coupled to the MDM waveguide with two movable baffles,has been studied.Fano resonance results from the interference between a wide continuous state related to the baffle and a narrow discrete mode produced by the slot cavity,respectively.The Fano line-shape can be dynamically regulated by altering the refractive indices of analytes between the two baffles,and the structural parameters keep unchanged.In addition,the sensing performances of the plasmonic structure has been investigated,which provides a solution for realizing tunable and on-chip sensor.