A new kind of tunable multi-channel wavelength demultiplexer (WDM) based on metal-insulator-metal (MIM) plasmonic nanodisk resonators with a metal block is proposed. The transmission properties of such structure are simulated by the Finite-Difference Time-Domain (FDTD) method, and the eignwavelengths of the disc resonator are calculated theoretically. It is found that the transmission characteristics of the filter can be easily adjusted by changing the geometrical parameters of the metal block of the nanodisk. The multi-channel WDM structure consisting of a plasmonic waveguide and several nanodisk resonators with metal block, by changing the parameter of metal block of nanodisk resonators, the filter shows the resonant mode filter function. Basing on this characteristic, a three-port wavelength demultiplexer is designed, which can separate resonant modes inside the nanodisk with high transmission up to 60%. It can find important potential applications in highly integrated optical circuits.
A surface plasmon resonance (SPR) sensor on an optical fiber endface with metallic rectangular slit array structure is presented. The finite-difference time-domain (FDTD) method was utilized to study the influence of structural parameters on the transmission spectrum and the refractive index (RI) sensing characteristic based on the two transmission peaks. The proposed sensor is compact and has the potential to be used in biomedical applications, having two transmission peaks with a sensitivity of 1209 and 500 nm per refractive index unit (RIU) respectively.