A plasmonic sensor is proposed, comprising a metal–insulator–metal (MIM) straight waveguide and a ring cavity with one stub (RCS). Using the finite element method, its transport properties are simulated and systematically analyzed. By optimizing the structure parameters, the sensor obtains the maximum sensitivity (S) of 2010 nm/RIU and the maximum figure of merit (FOM) of 49219.04 RIU⁻¹. It demonstrates a sensing resolution (SR) of 4.98 × 10⁻⁷ RIU in the detection of refractive index variation. Based on the optimized parameters, temperature sensing is investigated utilizing Polydimethylsiloxane (PDMS) as the temperature-sensitive medium, and the temperature sensitivity is found to be −0.90 nm/°C. In addition, multiple independently tunable resonances are achieved by adding a ring cavity (RC) above the straight waveguide. This derived structure enables the simultaneous detection of electrolyte samples (Na⁺ and K⁺) in blood with bio-sensing sensitivities reaching 0.1833 nm·dL/mg and 0.2 nm·dL/mg. These results have directive significance for the development of multifunctional and ultra-compact plasmonic sensor.

We propose metal-insulator-metal (MIM) plasmonic waveguide, in which metal is aluminum-doped zinc oxide (AZO) and insulator is air. The real part of relative dielectric constant is negative that is similar to the metal. Therefore, we call the AZO as metal. Owing to cutoff frequency of TM₀ model for the MIM waveguide being slightly larger than 193.5 THz, the MIM waveguide shows obviously slow light effect around the commonly used telecom frequency. Exploiting the dispersion relationship of MIM waveguide, we analyze the effect of core layer width for the MIM waveguide on slow group velocity, second-, and third-order dispersion. The core layer width of MIM waveguide is determined to simultaneously realize obviously slow light effect and the lower distortion for the pulse with width 200 fs, which is confirmed by simulation used the finite-difference time-domain method. The MIM waveguide potentially applied in optical delay lines is easily fabricated.

A metal–insulator–metal (MIM) waveguide system consisting of a MIM waveguide, a ring cavity, and a semi-ring cavity is proposed. Using the finite element method, the transmission characteristics of the MIM waveguide system are discussed under the different geometry parameters. By detecting the resonance wavelength and varying the refractive index, the sensing performance of the MIM waveguide system is analyzed. The proposed structure can be used as a refractive index sensor with the maximum sensitivity of 2412 nm/RIU. Due to isolating the ring cavity and semi-ring cavity, the independent tuning of double resonances can be realized by changing the refractive index of the insulator in the ring cavity or the semi-ring cavity. Benefiting from two independent refractive index sensing modes, the structure with two isolated resonators can realize the simultaneous measurement of glucose solution concentration and blood plasma concentration. The sensitivity of glucose solution sensing in the ring cavity is 0.13133 nm/(g/L). Meanwhile, the blood plasma concentration detection in the semi-ring cavity is realized with the sensitivity of 0.358 nm/(g/L). The system with two isolated cavities has the potential to be used as an efficient nano sensor, which can achieve simultaneous measurement of two parameters.