Now we add two cavities to the sensor structure and measure its performance (Fig. 10).
We change the refractive index of the middle cavity with a step of 0.01 from 1.14 to 1.2 and the refractive index of the waveguides and the other two cavities remain constant. Figure 11 shows the resulting transmission spectrum, which has three modes, in the wavelength range of 400 to 1600 nm.
We now calculate the sensitivity of the sensor, which according to Fig. 12 has the highest sensitivity for the refractive index n = 1.2 (in mode 3), which is equal to 1018 nm / RIU.
Next, we calculate the FIT and the quality factor Q and draw the corresponding diagrams (Fig. 13). According to the figure, the highest figure of merit (FOM) for the refractive index is n = 1.18 (in mode2) which is equal to 12.483 nm / RIU and the highest quality factor Q for the refractive index is n = 1.15 (in mode2) which is equal to With 19.089 nm / RIU.
Next, we change the structure of the sensor and change the coordinates and dimensions of the two upper and lower cavities (Fig. 14), to measure the quality of the sensor and create a suitable structure for the sensor.
As in the previous structure, we change the refractive index of the middle cavity by a step of 0.01 from 1.14 to 1.2 and the refractive index of the rest of the sensor structure remains constant. The transmission spectrum from the simulation can be seen in Fig. 15. This spectrum, which is displayed in the wavelength range of 400 to 1600 nm, has three modes. Mode 3 on the right side of the chart has more flexibility than changing the wavelength.
We now move on to measuring the sensor designed in Fig. 14 and computing the sensitivity coefficient, quality factor Q, and the figure of merit (FOM). First the coefficient diagram we obtain the sensitivity, which according to Fig. 16, the highest sensitivity is obtained at a refractive index of n = 1.16 (in mode3), which is equal to 1165 nm / RIU. Compared to the highest sensitivity obtained from the sensor in Fig. 10, this sensor has better performance and has reached a higher sensitivity. Therefore, changing the dimensions and coordinates of the cavities has improved the sensor.
By calculating and plotting the Diagrams of the figure of merit (FOM) and the quality factor Q, the performance measurement of this structure is completed (Fig. 17(. According to the figure, the highest the figure of merit (FOM) for the refractive index is n = 1.17 (in mode 2) which is equal to 15.128 nm / RIU and the highest quality factor Q is for the refractive index n = 1.2 (in mode 1) which is equal to 24.183 nm / RIU.