Fig. 2: Comparison between the flat-band BIC mode and other normal BIC modes.
From: Ultracompact multibound-state-assisted flat-band lasers
a, Calculated band diagrams of the daisy-like air-hole photonic crystal with flat-band BIC (top) and conventional circular air-hole structure with normal C6v-BIC. b, Near-field profiles in finite-sized cavities (L = 5a) corresponding to the fundamental mode of the E1 band (top; flat-band) and B′ band (bottom) in the corresponding data in a. c, Group indices for the representative modes computed from the corresponding Bloch-band structures. d,e, Near-field profiles of the fundamental modes belong to the two adjacent bands (B (d) and E2 (e) bands) with linear dispersion, for the cavity with L = 13a (top). Bottom, extracted electric-field intensity along the dashed line within the cavities. f, Calculated Q factors of the B, E1 and E2 modes with distinct band dispersion features, treating the pumped region as a lossless dielectric with absorbing boundaries (Methods). Here a flat-band BIC cavity with lattice parameters of a = 37.2 μm and r0 = 14.5 μm is adopted to exclude the influence of the multi-BIC, which will be discussed later in Fig. 3.
