Fate of the superradiant mode in a resonant Bragg reflector

Based on the first-principles theory of radiative correction, it is demonstrated that the well-known superradiant (SR) mode in a resonant Bragg reflector consisting of N layers loses its meaning when the frequency dependence of its radiative width becomes no longer negligible within its spectral width in the course of increasing N. Beyond this range of N, it evolves, together with a part of subradiant modes, into the states forming the light-reflecting photonic gap. On the other hand, the rest of the subradiant modes form very narrow light-transmitting modes in the gap region. This conclusion is reached by calculating the N dependence of the reflectance in frequency and time domains with the explicit consideration of a frequency-dependent radiative shift and width. The intrinsic limit of the speedup effect of the radiative decay of the SR mode is given for various cases.