Fig. 1. (a) Schematic graph of film stack based on Fano resonance Sub/Ag/LaTiO₃/Ag/MgF₂/GST/air (MD2MD1A); (b) calculated (left, ‘-desi’) and measured (right, ‘-expt’) reflectance of film stacks using LaTiO₃ (bottom) or TiO₂ (top) as D2 layer (the optical thickness was kept the same); (c) effective interface method.

Fig. 2. (a) Phase shift and reflectance of MDM structure (data from: Ag/LaTiO₃/Ag); (b) phase shift and reflectance of MA (data from: Ag/GST); (c) coupling of different damping rate oscillators or structures (MDM + MA); (d) phase shift and reflectance of coupled structure, MDMA (data from: Ag/LaTiO₃/Ag/GST).

Fig. 3. Four different Fano structures with varied continuum states and the same bound state. (a) MDMD (data from: Ag/LaTiO₃/Ag/MgF₂); (b) MDMA (data from: Ag/LaTiO₃/Ag/GST); (c) MDMAD (data from: Ag/LaTiO₃/Ag/GST/MgF₂); (d) MDMDA structure (data from: Ag/LaTiO₃/Ag/MgF₂/GST); color blocks beside are the calculated colors for (a), (b), (c), and (d) from top to bottom.

Fig. 4. (a) Phase curves and (b) reflectance spectra of these two states: Ag/LaTiO₃/Ag and Ag/MgF₂/GST, and their coupling unit Ag/LaTiO₃/Ag/MgF₂/GST (three graphs from top to bottom); (c) change in the thickness of LaTiO₃ to tune the abrupt phase change created by Ag/LaTiO₃/Ag.

Fig. 5. Total structure: Ag (100 nm)/LaTiO₃/Ag (14 nm)/MgF₂ (42 nm)/GST (7.5 nm). (a) Color palette calculated by varying the thickness of the dielectric LaTiO₃ from 45 to 120 nm when the gap is fixed at 5 nm; (b) reflectance spectra calculated by varying the LaTiO₃ from 45 to 125 nm at an interval of 10 nm; (c) color gamut in CIE 1931 chromaticity diagram to compare our structure with F–P cavities, sRGB gamut, and Adobe RGB gamut. The incidence angle is 0 deg. “Fano (single layer)” and “Fano (two layers)” mean the color range gotten by altering the thickness of one single layer (LaTiO₃) and two layers (LaTiO₃, MgF₂).

Fig. 6. Calculated and measured optical spectra of the structure proposed here. (a) Red sample; (b) green sample; (c) blue sample; (d) picture of three samples taken at an angle of less than 5 deg.