Spontaneous symmetry breaking of non-Hermitian coupled nano-cavities

Abstract

Experimental spontaneous symmetry breaking results are observed from a non-Hermitian coupled cavities device. In the experiment, when horizontally polarised incident light exceeds \(8 \text{m}\text{W}\), the symmetry-breaking threshold, vertically polarised transmitted light is also detected in addition to the horizontally polarised transmitted light, i.e. spontaneous symmetry breakdown of polarisation occurred. To elucidate more details on physics of the symmetry breakdown, theoretical modelling is also performed. Using nonlinear coupled mode theory (NCMT) equations, a power-related random splitting of the two handedness polarised lights is established, namely, right- or left- handed circular polarisation (RCP and LCP), at the resonance peak. In the numerical simulations, when incident power is above the symmetry-breaking threshold, the device will exhibit spontaneous symmetry breaking characteristics viz. appearance of an additional polarisation component in the output field. The additional polarisation direction is orthogonal to the linearly polarised incident light. These findings offer further understanding spontaneous symmetry breaking in non-Hermitian systems, and also demonstrate the potential applications of the proposed device in optical signal processing.