A review: Rise of PT-symmetry for laser applications

Abstract

In quantum mechanics, with the groundbreaking discovery of parity-time symmetry (PT-symmetry), Bender and Boettcher unfold the nature of the non-Hermitian Hamiltonian to exhibit real eigenvalues. This opened a new doorway to efficiently explore all the previously ignored quantum non-Hermitian systems. The analogy between the Schrödinger equation in quantum mechanics and the paraxial wave equation in optics spurred researchers to apply the concept of PT-symmetry to optical systems. On exploring the PT-symmetric optics experimentally, by engineering loss and gain in the system, a lot of applications have been reported. It includes single-mode lasers, coherent perfect absorber lasers (CPA lasers), exceptional point sensors (EPS), spectral and spatial filters, etc. In addition to linear theoretical models on PT-symmetry, nonlinear theoretical models and the corresponding experimental results have also been reported in the last few decades. This review article begins with the fundamental idea of PT-symmetry for beginners. Subsequently, we elucidate its advancements in the field of optics. Besides, we present the recent developments of various laser systems using PT-symmetry. Thus, this review intends to focus on novel theoretical and experimental works on PT-symmetry.