A detailed analytical study of an impurity-induced polariton band arising i
nside a spectral gap between lower and upper polariton branches is presente
d. Using the microcanonical method, we calculate the density of states and
the localization length of the impurity polaritons. Analytical results are
compared with numerical simulations, and excellent agreement is found. (C)
2000 Optical Society of America [S0740-3224(00)00709-8].