A plasmonic colour filter and refractive index sensor applications based on metal–insulator–metal square µ-ring cavities

In this paper, we proposed dual applications of a metal–insulator–metal (MIM) waveguide (WG) resonator design for filtering white light into individual colours and refractive index sensing applications. Six square µ-ring cavities of different sizes are side coupled to the MIM bus WG. By careful selection of the cavity size and distance between the bus WG and µ-ring cavities, the resonator can selectively couple to the intensity maxima of different photonic modes and, as a result, preferentially select any of the primary colours. The spectral characteristics of the resonator are comprehensively studied by varying the geometric parameters using the finite element method. This design can offer a sensitivity of 700 nm/RIU, with a figure of merit of 191.6. (paper)