A brief survey of the recent experimental and theoretical results on the low threshold distributed feedback (DFB) lasing in
chiral liquid crystals (CLC) and new original theoretical results on the localized optical modes  (edge (EM)  and
defect (DM) modes ) are presented. It is shown that EM and DM not only ensure a low DFB lasing threshold in the photonic
LCs but efficiently reveal themselves also in some other optical phenomena. An analytic theory of EM and DM is developed and
applied to the DFB lasing in CLC. The properties of the EM and DM are investigated. The dispersion equations for EM and DM
are found, analysed, solved analytically for some limiting cases, and solved numerically for the typical values of the
related parameters. The expressions determining the decay rate for these modes are presented. Lasing thresholds at the
frequencies corresponding to the spatially localized EM and DM in a CLC layer occur to be much lower than the ones for
conventional lasing. The options for a further reduction of the lasing thresholds connected with the pumping at the EM
and DM frequencies are predicted (and partially experimentally observed ). It is demonstrated that the analytic
approach applied to the DFB lasing allows to reveal some qualitative effects escaped from the researchers employing
the numerical methods and to predict new options for a low threshold lasing. Namely, the effect of anomalously strong
absorption at the DM frequency, a direct analogue of the corresponding effect at the EM frequency , is predicted .
It is shown also that the localized EM and DM reveal themselves in an enhancement of some inelastic and nonlinear optical
processes in photonic LCs. As examples the corresponding experimentally observed effects for the enhancement of nonlinear
optical second harmonic generation  and lowering of the lasing threshold  in photonic LCs are presented. New options
for the EM and DM application to the lasing in CLCs are discussed.
Acknowledgment: This work was supported by the RFBR grants 09-02-90417-Ukr_f_a and 10-02-92103-Jpf_a.
1. I. Kopp, Z.-Q. Zhang, and A. Z. Genack, Prog. Quant. Electron. 2003, 27(6), 369.
2.V.A.Belyakov and S.V.Semenov, JETP, 2009, 109, 687.
3. V.A.Belyakov, MCLC, 2008, 494, 127.
4. Y.Matsuhisa, Y.Huang, Y.Zhou et al., Appl.Phys.Lett., 2007, 90, 091114.
5. V.A.Belyakov, A.A.Gevorgian, O.S.Eritsian and N.V.Shipov, Zhurn.Tekhn.Fiz., 1987, 57, 1418 [Sov. Phys. Technical Physics, 1987, 32 (n7), 843-845, English translation].
6. K.Shin, H.Hoshi, D.Chang, K.Ishikawa and H.Takezoe, Optics Lett., 2002, 27, 128.