Role of the bus waveguide in the nonlinear reciprocity breaking in a Taiji microresonator

Optical devices which show different behaviors depending on the propagation direction of the light cannot be realized just by using optical passive systems in the linear regime because of the Lorentz reciprocity theorem (LRT). However, by using a non-Hermitian and nonlinear Taiji microresonator (MR) based on a silicon oxynitride (SiON) MR with an embedded S-shaped branch (see Fig. 1 (a) ) we have demonstrated non-reciprocity [1], [2]. In this work, we study the role of the bus waveguide and we show that it is possible to break LRT for different propagation directions. In particular, we evidence the role of the bus waveguide position asymmetry with respect to the Taiji MR and of the Fabry-Pérot (FP) oscillations generated by the waveguide facets.