Complex photonic crystals and complex perturbation

Recent great success of non-Hermitian photonics indicates that conventional photonics should be reconsidered by designing the full complex degree of freedom for the refractive index. In this talk, we discuss two orientations with this scenario, that is, complex photonic crystals and complex perturbation. Recently, we have succeeded in making various types of complex photonic crystals for which we separately control the symmetry and spatial pattern of the real and imaginary parts of index modulation. Here we show that these specially-designed complex photonic crystals exhibit interesting properties including non-Hermitian chiral singular points and reciprocal non-Hermitian skin effect. Second, we discuss the impact of complex perturbation to nanophotonic systems. Recently, we found that a very tiny localized complex perturbation to symmetric Hermitian systems produces chiral states, which is extended to various types of resonators and waveguides. These results show that the complex degree of freedom opens up new possibilities in nanophotonic systems.