On-chip experiment for chiral mode transfer without enclosing an exceptional point

Abstract

Adiabatically encircling an exceptional point (EP) in a two-dimensional parameter space usually leads to the flip of instantaneous eigenstates. However, encircling dynamically the EP will arouse chiral modes transfer. The obtained eigenstate is determined by the encircling direction. The effect is robust against the size of the encircling loop in the parameter space once the EP is enclosed in the loop. It has been reported theoretically that the effect can also be observed when the loop does not enclose EP but keeps it at a proper distance. Here we experimentally validate the theoretical prediction by designing and fabricating a silicon-on-insulator based subwavelength grating waveguides structure. The chiral modes transfer is achieved via motivating and detecting the even and odd modes around the telecommunication wavelength. The results provide a more robust way for studying the topological properties of the non-Hermitian system.