“…In particular, it reveals locations of photonic band gaps, for which the existence of electromagnetic field inside the photonic crystal is prohibited (in case of a photonic crystal built of a finite number of layers this is not strictly possible, because a part of electromagnetic field always leaks out of the photonic crystal, however, electromagnetic field can be strongly extinguished, indeed). This function can be used to analyze not only a perfect photonic crystal, but also with an intentionally created defect ( [13]) or -as it is done in this paper -with multiple, random defects of layer thickness.…”