LOCALIZED OPTICAL MODES AND LOW THRESHOLD LASING IN PHOTONIC SPIRAL MEDIA Belyakov Vladimir A., Senior Researcher, Professor. <...> One of the most studied media of this kind are the cholesteric liquid crystals. <...> It is why the localized opical modes and lasing in photonic spiral media are studied for the certainty at the example of chiral liquid crystals (CLCs). <...> The chosen here model (absence of dielectric interfaces in the studied structures) allows one to get rid off the polarization mixing at the surfaces of the CLC layer and the defect structure (DMS) and to reduce the corresponding equations to the equations for the light of diffracting in the CLC polarization only. <...> As specific cases are considered DMS with an active (i.e. transforming the light intensity or polarization) defect layer and CLC layers with locally anisotropic absorption. <...> It is shown that the active layer (excluding an amplifying one) reduces the DM lifetime (and increase the lasing threshold) in comparison with the case of DM at an isotropic defect layer. <...> The case of CLC layers with an anisotropic local absorption is, in particular, analyzed and it is shown that due to the Borrmann effect the EM life-times for the EM frequncies at the opposite stop-bans edges may be signifinately different and concequently the lasing threshold for the EM frequencies at the both stop-band edges are different. <...> Introduction Recently there have been much activities in the field of localized optical modes, in particular, edge modes (EM) and defect modes (DM) in chiral liquid crystals (CLCs) mainly due to the possibilities to reach a low lasing threshold for the mirrorless distributed feedback (DFB) lasing [1-4] in CLCs. <...> The corresponding EM and DM in CLCs, and more general in spiral media, are very similar to the EM and DM in one-dimensional scalar periodic structures. <...> In the present work, analytical solutions of the EM and DM (associated with an insertion of a layer in the perfect cholesteric structure and CLCs with local anisotropy of absorption) are presented and some limiting cases simplifying the problem are considered. 2. <...> We assume that the CLC is represented by a planar layer with a spiral axis perpendicular to the layer surfaces (Figure 1). <...> We also assume that the average CLC dielectric constant coincides with the dielectric constant of the ambient medium. <...> This assumption practically <...>