Figure 2
From: Formation mechanism of guided resonances and bound states in the continuum in photonic crystal slabs
(a) Band structure and (b) quality factors of the guided resonances and BICs in the system illustrated in Fig. 1b. (a) Yellow shaded area is where there is only one leaky channel in the surrounding medium. The blue (green) solid curve is the dispersion of guided resonances that are even (odd) in x. BICs are marked with red plus signs: ① and ③ are protected by symmetry, while ② and ④ are not. Circles are FDTD simulation results. The grey curves are guided modes below the light line. Red dashed lines in (b) mark the location of BICs not protected by symmetry. (c) Electric field patterns of the BICs. (d) Magnitudes of the mode-expansion coefficients in the slab C (upper panel) and outside the slab T (lower panel) for the BIC ④. Red dots are components propagating in the x direction (where βm or γm is real); blue dots are evanescent components with imaginary wave vector along the x direction. The structural parameters are: εA = 4.9, εB = 1, h = 1.4a, d = 0.5a.
