  In this paper, a bilateral asymmetric equilateral triangular ring (ETR)
band-stop filter based on metal-insulator-metal (MIM) waveguide is proposed.
The transmission spectrum and electric field distribution of the filter are
simulated and theoretically investigated by finite difference time domain
(FDTD) and coupled mode theory (CMT) method. The results show that changing the
number and position of resonant cavities can adjust the transmission
characteristics of the filter. The minimum transmission and sensitivity of this
filter is 0.19% and 1149 nm/RIU, respectively. The filters have broad prospects
in the highly integrated optical circuits and refractive index sensor.
