We consider parity-time (PT) symmetric arrays formed by N optical waveguides with gain and N waveguides with loss. When the gain-loss coefficient exceeds a critical value γc, the PT-symmetry becomes spontaneously broken. We calculate γc(N) and prove that γc→0 as N→∞. In the symmetric phase, the periodic array is shown to support 2N solitons with different frequencies and polarisations.

http://arxiv.org/abs/1311.4123
Optics (physics.optics); Mathematical Physics (math-ph); Pattern Formation and Solitons (nlin.PS)

We show that the parity-time (PT) symmetric coupled optical waveguides with gain and loss support localised oscillatory structures similar to the breathers of the classical \(\phi^4\) model. The power carried by the PT-breather oscillates periodically, switching back and forth between the waveguides, so that the gain and loss are compensated on the average. The breathers are found to coexist with solitons and be prevalent in the products of the soliton collisions. We demonstrate that the evolution of the small-amplitude breather’s envelope is governed by a system of two coupled nonlinear Schrodinger equations, and employ this Hamiltonian system to show that the small-amplitude PT-breathers are stable.

http://arxiv.org/abs/1211.1835
Pattern Formation and Solitons (nlin.PS); Optics (physics.optics)