General characteristics of localization in stratified media with random loss and gain

Localization in multi-layer stratified media with gain and loss is considered. The localization length is studied as a function of wavelength over a wide spectral range, and it is demonstrated that, in many cases, the localization characteristics of multiple layer stacks are identical to those exhibited by a single layer. It is shown that these properties are associated with six physical effects, giving rise to six regions with different variations of localization with wavelength. These six regions and the transition wavelengths between them are characterized by a sequence of simple rules that determine the general dependence of localization on wavelength and which are robust for stacks of arbitrary length.