Theoretical approach to breaking the angular dispersion limit of Fano resonances in thin-film optics

Fano resonances in thin-film optics exhibit strong angular dispersion, which severely degrades the Q factors and significantly distorts the lineshapes. In this Letter, we theoretically demonstrate an angle-dispersion-free Fano resonance in a heterostructure composed of a plasmonic layer and two one-dimensional photonic hypercrystals. This fascinating property of the Fano resonance originates from the interference between an angle-dispersion-free continuum and an angle-dispersion-free optical Tamm state. As the incident angle increases from 0 to 80 degrees, the Fano dip exhibits an extremely small wavelength shift of less than 0.1%, while its Q factor remains highly stable. Our work breaks the angular dispersion limit of Fano resonances in thin-film optics.