Hermiticity-tunable beam reshaping: localization, recurrence and group velocity oscillation

Abstract

We propose a novel method to reshape the light beam in a Hermiticity-tunable photonic lattice with PT symmetric perturbations. By adjusting the PT perturbations, the Hermiticity of the system varies alternatively, further resulting in the periodic oscillations of the group velocity (v g ) as well as the group velocity dispersion (GVD). Once the values of v g and its corresponding GVD recover and the averaged group velocity (v ḡ ) is zero, the light beam will be localized and recur at these Hermitian points. Further study indicates that GVD plays a key role in the evolution of the light beam, larger positive dispersion [Re(GVD)] and lower magnitude of Im(GVD) lead to higher peak energy of the light field. Our work provides a non-resonant way to control the light propagation and to reshape the group velocity distribution, which may have promising applications in all-optical circuit, optical sensor and optical communications.We propose a type of Hermitian-tunable photonic lattice with perturbation of PT symmetry. Such perturbations will introduce an imaginary phase factor Φ into the coupling constant. In consequence, the dispersion relations of such a system is Φ dependent and the Hermiticity of such a system will be tunable. Further study indicates that the perturbation will result in the oscillations of the group velocity (v g ) as well as the group velocity dispersion (GVD) along the propagation direction. Light will be dynamically localized and recur at certain Hermitian points, at which v g and GVD are recovered and averaged group velocity (v ḡ ) is zero.