Polariton Local States in Periodic Bragg Multiple Quantum Well   Structures
  We analytically study optical properties of several types of defects in Bragg multiple quantum well structures. We show that a single defect leads to two local polariton modes in the photonic band gap. These modes lead to peculiarities in reflection and transmission spectra. Detailed recommendations for experimental observation of the studied effects are given. 
Lev I. Deych, A. Yamilov, and A.A. Lisyansky