Fig. 1. (a) Three-dimensional structure diagram; (b) plan view of structure unit.

Fig. 2. Fabrication for the proposed structure.

Fig. 3. (a) Color plot of the transmission spectra with different lengths of metal bars; (b) transmission when the lengths of the metal bars are from 50 to 66 µm; (c) fitting curve of Fano resonance when the length of L is 56 µm; (d) transmission of MICMT and simulation when the lengths of the metal bars are 62, 60, and 58 µm, respectively. By curve fitting, the decay time of the internal losses, respectively, are about τ₁₀ = 4000 fs, τ₂₀ = 8000 fs, and τ₃₀ = 500 fs. The decay time of coupling and the total coupling phases, respectively, are about τ₁ = 400 fs, τ₂ = 8000 fs, τ₃ = 250 s, φ₁ = 0.2π, φ₂ = −0.3π, φ₃ = −0.1π; τ₁ = 400 fs, τ₃ = 250 s, φ₁ = 0.2π, φ₃ = −0.1π; τ₁ = 400 fs, τ₂ = 8000 fs, τ₃ = 250 s, φ₁ = 0.2π, φ₂ = −0.3π, φ₃ = −0.1π. (e) Quadrupole modes and (f) dipole modes when the lengths of the metal bars are 55 µm.

Fig. 4. (a) Single, double, and triple metal bars structure unit; (b) FWHM under different lengths; (c) ratio of Fano intensity to FWHM under different lengths; (d) Fano intensity, Q factor, and Q × I under different lengths.

Fig. 5. Simulated field enhancement of the triple metal bars. (a) and (b) show color plots of the field enhancement for different lengths in the triple metal bars, respectively; (c) electric field enhancement and (d) magnetic field enhancement for the lengths of 53, 55, 59, and 60 µm in the triple metal bars, respectively; (e) electric field enhancement and (f) magnetic field enhancement corresponding to the green dotted lines in (a) and (b), respectively.

Fig. 6. (a), (d), (g) Electric, (b), (e), (h) magnetic fields, and (c), (f), (i) surface current at the Fano resonance. (a), (b), (c) The length is 59 µm; (d), (e), (f) the length is 55 µm; (g), (h), (i) the length is 50 µm.

Fig. 7. (a) Dependence of transmission on the refractive index increased from 1.3 to 1.6 under the thickness of 70 µm; (b) dependence of transmission on the analyte thickness increased from 10 to 70 µm under the refractive index of 1.6; (c) frequency shift under different refractive indices of analyte extracted from (a); (d) frequency shift under different analyte thicknesses extracted from (b).

Fig. 8. Angular response for the triple metal bar length of 55 µm: (a) simulated transmission contour plot under TM-polarized incidence; (b) simulated transmission curves with incidence angles from 10° to 24°; (c) field distribution of Mode 1 and Mode 2 at 10° and 24°, respectively.

Table 1. Properties of BIC-Based Metasurface Sensors