Various studies have been conducted to understand non-Hermitian systems with the recognition that the interaction between gain and loss can lead to entirely new and unexpected properties.

In our laboratory, we have been conducting various theoretical studies and actual device development using the exceptional point (EP), which is the degeneracy point of eigenvalue in such a non-Hermitian system.

Topological operations around an EP and anti-adiabatic jump theoretical studies, broadband asymmetric mode transfer through encircling EP, broadband non-reciprocity through non-linear gain saturation, and non-Hermitian waveguide applications such as on-chip passive silicon optical isolator with broadband operation have been studied. By using such topological properties and non-Hermitian system, the scale of device can be reduced compared to the existing device, and the advantage of robustness against errors in the fabrication can also be expected.