Study on the fano resonance of coupling M-type cavity based on surface plasmon polaritons

The metal-insulator-metal (MIM) waveguide structure consisting of an M-type cavity and a baffle is proposed. Through the interaction between the discrete state and the continuous state by the M-type cavity and the baffle, the structure possesses a distinctly sharp asymmetric Fano resonance line. For positive M-type cavity structure, the shape of transmission spectrum can be adjusted by the structure parameters. The wavelength of the resonant peak has a linear relation with the length and width of the cavity, and has very good flexibility in the design and adjustment of structure. The ultra-sharp spectrum contributes to the sensitivity of structure which can reach up to 760nm/RIU and the maximum figure of merit is 9.9×104. For improved symmetrical M-type cavity structure, the simulation results show that the sensitivity reaches 780nm/RIU and the maximum figure of merit is 1.56×105. Its performance has been further enhanced. The structure may have a number of important applications in the field of nano-sensors.