The necessity for cheaper and more efficient sensors has been the main motivation for the use of Metal-Insulator-Metal (MIM) sensors. In this paper, a micro-dimensional refractive index MIM sensor based on surface plasmon polaritons is presented. This sensor has a ring-hexagonal resonator and a pair of squares-ring resonators that are connected to each other. For the proposed structure, magnetic field profile, transmission spectrum, and important sensor parameters such as sensitivity are obtained through the finite-difference time-domain (FDTD) method. By optimizing the dimensions of the resonators, we achieved a sensitivity equivalent to 2115 nm/RIU in the first mode and 2180 nm/RIU in the second mode. The FOM values for the first and second modes were 118.25 RIU-1 and 120.208 RIU-1, respectively. The results show that the ring-hexagonal resonator significantly improves the sensor parameters in both modes. These enhancements can be considered unique due to the simple structure presented and as a result the reduction of construction costs.

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In this research work, “the cavity plasmon multi-mode resonance-based refractive index sensor with ultra-high sensitivity” is presented. The proposed sensor is the metal-insulator-metal nanostructure including the bus waveguide coupled to the hexagonal-ring resonator with rectangular air stubs. The transmittance properties, electric field profile, and magnetic field profile are investigated theoretically and numerically for three types of resonator structures by using the finite-difference time-domain method. Adding the air stubs to the ring resonator structure improves the light-matter interaction and effects of cavity plasmon resonances. The high sensitivity of 1725.5 nm/RIU, 3445 nm/RIU, and 5770 nm/RIU was achieved for mode 1, mode 2, and mode 3 of 6-stub resonator (case 3), respectively. The results show that case 3 enhances the maximum sensitivity by about 8% for none-stub resonator (case 1) and 91% for 2-stub resonator (case 2). The figure of merit is 30.8 RIU-1 in mode 1, 74.9 RIU-1 in mode 2, and 58.6 RIU-1 in mode 3. The presented sensor can be used as a biosensor for glucose detection.