Floquet higher-order exceptional points and dynamics in PT-symmetric quadrimer waveguides

We investigate the effect of periodic modulation on PT-symmetry recovery, higher-order exceptional points (EPs) and dynamics for a periodically modulated PT-symmetric quadrimer waveguide system. It is analytically and numerically revealed that the periodic modulation not only can restore the broken PT symmetry, but also can manipulate the PT symmetry by tuning modulation amplitude. Furthermore, we found that multiple EPs can emerge, and as the modulation amplitude vary, these EPs can collide and merge, leading to higher-order Floquet singularities. By defining average relative light intensity distribution, we explore the dynamical characteristics nearby these EPs. It is found that we can control the light tunneling direction of optical quadrimer waveguide via periodic modulation and proper choice of gain/loss parameters. Graphical abstract