LAUSR

Achieving exact balance between spatially separated gain and loss is generally regarded as a necessary condition for parity–time (PT)-symmetric optical systems [1]-[12]. We introduce generalized PT (gPT)-symmetric optical structures, which have an asymmetric and unbalanced gain-loss profile, while exhibiting similar scattering properties and phase transitions as their traditional PT-symmetric counterparts. In particular, we show that the concept of gPT-symmetry may help reducing the threshold gain in achieving newly discovered PT-enabled applications, such as the coherent perfect absorber (CPA)-laser and exceptional points. The concept proposed herein will facilitate the practice of PT-symmetric optical and photonic devices by offering greater design flexibility to tailor gainloss profiles and their thresholds.