CP symmetry in optical systems

TL;DR

This paper models a dual-core optical waveguide system exhibiting CP symmetry, demonstrating how linear and nonlinear regimes produce distinct states, including expanding Gaussian states and stable solitons, with implications for optical symmetry studies.

Contribution

It introduces a novel optical system model that realizes CP symmetry and explores its behavior under linear and nonlinear conditions, revealing new soliton solutions.

Findings

Linear system produces expanding Gaussian states

Nonlinear system supports stable oscillating and gap solitons

CP symmetry is broken by intra-core nonlinearity

Abstract

We introduce a model of a dual-core optical waveguide with opposite signs of the group-velocity-dispersion (GVD) in the two cores, and a phase-velocity mismatch between them. The coupler is embedded into an active host medium, which provides for the linear coupling of a gain-loss type between the two cores. The same system can be derived, without phenomenological assumptions, by considering the three-wave propagation in a medium with the quadratic nonlinearity, provided that the depletion of the second-harmonic pump is negligible. This linear system offers an optical realization of the charge-parity ($\mathcal{CP}$) symmetry, while the addition of the intra-core cubic nonlinearity breaks the symmetry. By means of direct simulations and analytical approximations, it is demonstrated that the linear system generates expanding Gaussian states, while the nonlinear one gives rise to broad oscillating solitons, as well as a general family of stable stationary gap solitons.