Optical fluxes in coupled PT-symmetric photonic structures
AbstractIn this work we first examine transverse and longitudinal fluxes in a PT-symmetric photonic dimer using a coupled-mode theory. Several surprising understandings are obtained from this perspective: The longitudinal flux shows that the PT transition in a dimer can be regarded as a classical effect, despite its analogy to PT-symmetric quantum mechanics. The longitudinal flux also indicates that the so-called giant amplification in the PT-symmetric phase is a subexponential behavior and does not outperform a single gain waveguide. The transverse flux, on the other hand, reveals that the apparent power oscillations between the gain and loss waveguides in the PT-symmetric phase can be deceiving in certain cases, where the transverse power transfer is in fact unidirectional. We also show that this power transfer cannot be arbitrarily fast even when the exceptional point is approached. Finally, we go beyond the coupled-mode theory by using the paraxial wave equation and also extend our discussions to a PT diamond and a one-dimensional periodic lattice.