IMPURITY MODES IN ONE-DIMENSIONAL PHOTONIC CRYSTALS-ANALYTIC APPROACH

We investigate the impurity problem in one-dimensional photonic crysta ls using the two-band Bloch wave approximation. The impurity level, as the lasing mode, is described in terms of the width and the dielectri c function of the impurity, which are in fair agreement with the numer ical data by the transfer matrix method. The maximum field intensity a nd the strongest spatial localization occur when the impurity mode is at midgap, indicating large gain enhancement of the lasing mode. The t hreshold gain and the optimal conditions for the impurity are evaluate d. Effects of surface variations are also analysed to further improve the efficiency of the lasing system.