Universal coupled-mode theory formulation of quasi-normal modes in a 1D photonic crystal

In terms of coupled-mode theory, only two real-valued normalized parameters are needed for describing the spectral properties of any 1D photonic crystal of finite size made of lossless materials: detuning (delta L) with respect to the Bragg condition and coupling strength (kappa L). As far as its quasi-normal mode (QNM) spectrum is concerned, the usual ``complex frequency'' concept can be replaced by an effective ``complex detuning'' (delta L + i alpha L), thus establishing a formal connection with the modal cartography, in the (kappa L,alpha L) plane, of purely index-coupled distributed-feedback lasers of normalized gain alpha L.