Optical Properties And Sensing Applications Of Plasmonic Ring Cavities

Surface plasmon polaritons(SPPs),are electromagnetic Surface waves that are electromagnetic oscillations caused by the interaction of photons and free electrons on metal surfaces.Due to the limitation of diffraction,traditional photonic devices,such as light emitting devices,detectors,optical waveguide devices,optical switches,etc.,can not meet the requirements of high speed and high integration in the practical applications.Surface plasmons can break the diffraction limit and achieve optical control at the subwavelength scale.A new approach is provided by nano-all-optical communication.At present,the study of surface plasmons has been a hot topic.SPPs,along the metal-dielectric(MD)interface,can be controlled by changing the surface structure of the Metal,providing a new method for manipulating the electromagnetic wave propagation.Among all the plasmonic waveguides,metaldielectric-metal(MDM)waveguide has been widely investigated due to the simple structure,ease of fabrication,strong localization and low propagation loss.The research of this paper is as follows:(1)Based on the finite-difference method in the time domain(FDTD)and coupledmode theory(CMT),the frequency-selecting and sensing properties,in plasmonic system composed of waveguide and ring cavity with embedded metal bar,have been numerically and theoretically demonstrated.The added metal rod doubles the number of resonant mode of the system and increases the number of frequency selection.Modulating the location of metal bar introduces the periodic variation of transmission spectra,which provides a new degree of freedom for controlling the resonant modes.In addition,the sensitivity and figure of merit(FOM)reach 1627.5 nm/RIU and 37.8935,respectively.The results provide theoretical basis for designing ultracompact optical switch,sensor and filter.(2)A simple and tunable plasmonic sensor has been designed.The system consists of an MDM waveguide embedded with a metal baffle and a ring cavity.The Fano resonance occurs form the interference between the continuous state generated by the baffle and the discrete mode generated by the ring cavity.By adjusting the position of the baffle,the transmission characteristics can be dynamically tuned.The maximum FOM and sensitivity can reach 20480 and 690 nm/RIU,respectively.Besides,the influences of the rod on the Fano resonance effect have also been studied,which introduces the multiple Fano resonances and enhances the sensing performances.