Optical symmetric pushing, uni-/bi-directional null, and pulling-pushing flipped forces in one dimensional PT-symmetric photonics

TL;DR

This paper explores how PT-symmetric photonic structures can produce various optical forces, including pushing, pulling, and null forces, depending on symmetry phases and incident wave configurations, with potential applications in optomechanics.

Contribution

It introduces a generalized parametric space framework to analyze optical forces in PT-symmetric systems, revealing novel force behaviors and phase-dependent phenomena.

Findings

Symmetric pushing in exact symmetry phase

Null and bi-directional null forces at exceptional point

Pulling-pushing flipped forces in broken symmetry phase

Abstract

We discuss the optical forces exerted on parity-time (PT) symmetric heterostructures under normal incidence of a single and two counter-propagating plane waves. The underlying strategy is through generalized parametric space, stemming from consideration of PT-symmetry condition and Lorentz reciprocity theorem. In such a generalized parametric space, we are able to not only exhaustively indicate various PT phases and extraordinary wave phenomena, but also deduce the directionality and magnitudes of optical forces. We find that when the system is illuminated by a normally incident wave, it can exhibit the symmetric pushing effect in the exact symmetry phase, uni-directional null (UNF) and bi-directional null force (BNF) at the exceptional point (EP), and pulling-pushing flipped forces in the broken symmetry phase, with BNF found at the pushing-pulling turning point. In two counter-propagating plane waves interference, the magnitudes as well as the directionality of resultant optical force can be tuned by relative phase of incident waves. More interestingly, we observe that there has a null force independent of the relative phase occurred in a specific region of broken symmetry phase and exceptional point. In addition, we offer several PT-symmetric heterostructures to support our findings. Our results may be beneficial for applications in PT optomechanics and force rectifiers.